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Thoracic Oncology
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Prognostic Impact of Minimal Pleural Effusion in Non–Small-Cell Lung Cancer
Abstract
Minimal (< 10 mm thick) pleural effusion (PE) may represent an early phase of malignant PE, but its clinical relevance has rarely been studied. Therefore, we examined the proportion of minimal PE in patients with non–small-cell lung cancer (NSCLC) and its impact on survival. We also considered possible accumulation mechanisms in our data set.
On the basis of PE status from chest computed tomography scans at diagnosis, 2,061 patients were classified into three groups: no PE, minimal PE, and malignant PE. Twenty-one variables associated with four factors—patient, stage migration, tumor, and treatment—were investigated for correlation with survival.
Minimal PE presented in 272 patients (13.2%). Of 2,061 patients, the proportion of each stage was the following: 5.2% stage I, 10.9% stage II, 13.2% stage IIIA, 23.8% stage IIIB, and 13.9% stage IV. Minimal PE correlated significantly with shorter survival time than did no PE (median survival time, 7.7 v 17.7 months; log-rank P < .001), even after full adjustment with all variables (adjusted hazard ratio, 1.40; 95% CI, 1.21 to 1.62). Prognostic impact of minimal PE was higher in early versus advanced stages (Pinteraction = .001). In 237 patients (87.8%) with minimal PE, pleural invasion or attachment as a direct mechanism was observed, and it was an independent factor predicting worse survival (P = .03).
Malignant pleural effusion (PE) is defined by the presence of malignant cells in pleural fluid or biopsy. The accurate evaluation of PE became more important for tumor staging in the seventh edition of TNM classification, in which its status was changed from T4 to M1a.1 Thoracentesis and/or pleural biopsy are the first diagnostic steps in determining PE characteristics. However, these procedures are not recommended when PE presents as a minimal thickness (< 10 mm) on lateral decubitus radiography or chest computed tomography (CT) scans.2,3 Alternatively, the more invasive approach of video-assisted thoracoscopic surgery can be considered to identify whether fluid contains malignant cells. However, this requires general anesthesia and raises concerns about mortality or morbidity, especially in patients with advanced-stage disease.
For staging in patients with minimal PE, guidelines have taken an ambiguous or different stand between small-cell lung cancer and non–small-cell lung cancer (NSCLC).1,4 The National Comprehensive Cancer Network guideline recommends that a PE too small to warrant thoracentesis should not be included in staging of small-cell lung cancers.4 Therefore, the presence of minimal PE is deemed limited-stage disease. Conversely, minimal PE is not covered in the recommendations for staging NSCLCs.1,4
Chest CT scans have been used in staging disease for more than two decades, and the incidence of adenocarcinoma is increasing in most countries. Although there have been no epidemiologic studies, the proportion of patients with minimal PE at diagnosis is expected to be significantly increasing. Furthermore, minimal PE might represent an early phase of malignant PE or severe comorbid disease that would confer prognostic impact. If so, then it may be an important characteristic for clinicians in staging the disease and selecting optimal treatment.
For such reasons, we set out to evaluate the proportion of minimal PE in patients with NSCLC from a retrospective cohort and the impact of this characteristic on prognosis of survival and to examine mechanisms involved in its accumulation.
A cohort of 2,340 consecutive patients diagnosed histologically with stage I to IV NSCLC at Inha University Hospital (from 2002 to 2010) was considered initially in this study (Fig 1). The stage of all patients was defined according to the seventh edition of the TNM classification.1 To maintain quality of information on staging, patients who underwent noncontrast chest CT scans (n = 105) or who did not undergo brain imaging (n = 117) or whole-body bone scans (n = 54) were excluded. All patients underwent a staging work-up and were treated at the hospital. No patient received crizotinib or was enrolled onto clinical trials for tyrosine kinase inhibitors or other monoclonal antibodies. All information on prognostic variables was collected prospectively from the records of the Lung Cancer Cohort of Inha University Hospital. The study protocol was approved by the institutional review boards of the university hospital, and informed consent by the patient was waived.
Fig 1. Flow chart for enrollment and classification of patients. (*) Nine patients were reclassified into malignant pleural effusion from minimal pleural effusion (pleural nodules in 5 patients; cytologically positive after pleural effusion rapidly increased in 3 patients) and no pleural effusion (multiple malignant pleural nodules found in surgical resection in 1 patient). CT, computed tomography; MRI, magnetic resonance imaging.
Patient-related variables included age, sex, smoking habit, Eastern Cooperative Oncology Group performance status (ECOG PS), any weight loss during the 6 months before diagnosis, and serum levels at diagnosis of hemoglobin, albumin, alkaline phosphatase, and calcium. The Charlson comorbidity index (CCI) score was calculated for each patient, with 19 diseases weighted by impact on mortality.5 The variable related to stage migration was rated according to whether or not positron emission tomography (PET) scans had been taken. Tumor-related variables were histology, epidermal growth factor receptor (EGFR) mutation, T stage, tumor size, N stage, M stage, and number of organs affected by metastasis. Finally, treatment-related variables consisted of curative treatment, palliative treatment, and no treatment. Curative treatment was defined by stages: surgery alone, (neo) adjuvant chemotherapy, or concurrent (or sequential) chemoradiotherapy therapy for stages I through IIIA; cytotoxic chemotherapy or concurrent (or sequential) chemoradiotherapy therapy for stage IIIB; and cytotoxic chemotherapy or targeted therapy for stage IV.
Results from PE analysis at diagnosis were evaluated by two pulmonologists (H.-S.N. and S.-N.L.). All chest CT scans at diagnosis were reviewed by a radiologist (K.-H.L.) to evaluate the presence of pleural fluid, any laterality, and thickness. Evaluation was blinded to data on the patients, including their survival status. According to the presence of pleural fluid and its thickness (judged relative to a criterion of 10 mm on chest CT scans), patients were classified initially into three groups: no PE, minimal PE (< 10 mm thick), and malignant PE. Of 280 patients who initially met the criterion for minimal PE, five showed pleural nodules; in three others, the PE increased rapidly and malignant cells were found by cytology before treatment. These eight patients were reclassified into the malignant PE group. Multiple malignant pleural nodules were found in surgical resection in one patient initially staged as IB who was subsequently reclassified as malignant PE. No patients in the minimal PE group underwent any diagnostic evaluation for pleural fluid before commencement of treatment or at surgical resection. The presence of minimal PE was not taken into account in tumor staging.
The malignant PE group consisted of 392 patients, with positive findings of malignant cells in 237 (61%), no malignant cells but exudative PE in 71 (18%), pleural nodule(s) in 24 (6%), and no diagnostic work-up in 60 (15%). A total of 2,061 patients with NSCLC were finally included in this study.
Possible causes for accumulation of PE were determined by the radiologist and two pulmonologists from review of chest CT scans and bronchoscopy results, laboratory data, and comorbid diseases at diagnosis. They were classified as direct, indirect, or other mechanisms (Appendix Table A1, online only).
Overall survival was measured as an outcome and estimated from the time of diagnosis until death as a result of all causes. Only 21 patients died of other cancers or causes. There were 1,931 patients who died in our hospital. Otherwise, the date of death was obtained principally by contacting relatives of the patients (n = 529). For 59 patients who could not be contacted because they were lost to follow-up after hospital discharge, information on their survival was collected from the Korean Ministry of Security and Public Administration.
Distribution of the 21 variables according to the patients' PE status was assessed by using χ2 tests. The effect of an individual variable or PE status on survival was estimated by using the Kaplan-Meier method and log-rank testing. The hazard ratios (HRs) and 95% CIs were determined by using a Cox proportional hazard model. The hazards were calculated in an unadjusted model and then adjusted for each group of prognostic variables as potential confounders; patient-related variables, stage migration, and tumor- or treatment-related variables were added separately to the unadjusted model. The proportion hazards assumption was examined with a plot of –log [−log (survival functions)] against log (follow-up time) and Schoenfeld residuals. The curves for minimal PE remained close together over the entire follow-up period and did not suggest nonproportionality (data not shown). Clinical stage and T and M stages were overlapped for the analysis with tumor size, number of organs in which metastasis occurred, and PE status, respectively, and then excluded. The fully adjusted model included 17 variables (Tables 1 and 2). Performance of the model was evaluated by Harrell's c-index. To examine effect modification of the PE by stage, we added an interaction term to the Cox proportional hazard model. All significance testing was done at the two-sided P < .05 level. Analyses were performed by using the IBM SPSS statistical software package version 19.0 (SPSS, Chicago, IL) and STATA version 12.1 (STATA, College Station, TX).
|
| Variable | No PE (n = 1,397) | Minimal PE (n = 272) | Malignant PE (n = 392) | Ptrend | ||
|---|---|---|---|---|---|---|
| HR | HR | 95% CI | HR | 95% CI | ||
| Unadjusted | 1 | 2.33 | 2.04 to 2.65 | 2.80 | 2.48 to 3.16 | < .001 |
| Patient-related variables | 1 | 1.67 | 1.45 to 1.92 | 2.18 | 1.90 to 2.51 | < .001 |
| Demographics: age, sex, smoking habit | 1 | 2.19 | 1.92 to 2.50 | 3.07 | 2.70 to 3.49 | < .001 |
| Tumor burden: ECOG PS, weight loss, hemoglobin, albumin, alkaline phosphatase, calcium | 1 | 1.83 | 1.59 to 2.11 | 2.14 | 1.87 to 2.45 | < .001 |
| Comorbidity: CCI score | 1 | 1.98 | 1.73 to 2.26 | 2.40 | 2.12 to 2.72 | < .001 |
| Stage migration: PET | 1 | 2.30 | 2.02 to 2.63 | 2.75 | 2.44 to 3.11 | < .001 |
| Tumor-related variables: histology, EGFR mutation, tumor size, N stage, No. of organs affected by metastasis | 1 | 1.64 | 1.43 to 1.88 | 2.19 | 1.91 to 2.51 | < .001 |
| Treatment: no v yes* | 1 | 2.31 | 2.02 to 2.64 | 2.83 | 2.50 to 3.20 | < .001 |
| Final fully adjusted model† | 1 | 1.40 | 1.22 to 1.62 | 1.86 | 1.59 to 2.17 | < .001 |
Abbreviations: CCI, Charlson comorbidity index; ECOG PS, Eastern Cooperative Oncology Group performance status; HR, hazard ratio; PE, pleural effusion; PET, positron emission tomography.
*First-line treatments for patients with stage I to IIIA: surgery alone, (neo) adjuvant chemotherapy, or concurrent (or sequential) chemoradiation; stage IIIB: concurrent (or sequential) chemoradiation or chemotherapy alone; stage IV: palliative chemotherapy or targeted therapy.
†The model included sex, age, smoking habit, CCI score, ECOG PS, weight loss, hemoglobin, albumin, alkaline phosphatase, calcium, histology, EGFR mutation, tumor size, N stage, No. of organs affected by metastasis, PET, and treatment.
|
| Variables | Minimal PE | Malignant PE Stage IV (n = 392) | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Stage I (n = 20) | Stage II (n = 16) | Stage IIIA (n = 30) | Stage IIIB (n = 59) | Stage IV (n = 147) | ||||||||
| HR | 95% CI | HR | 95% CI | HR | 95% CI | HR | 95% CI | HR | 95% CI | HR | 95% CI | |
| Unadjusted | 3.37 | 1.93 to 5.89 | 2.10 | 1.14 to 3.88 | 2.12 | 1.39 to 3.23 | 1.65 | 1.22 to 2.21 | 1.38 | 1.16 to 1.63 | 1.37 | 1.19 to 1.57 |
| Patient-related variables | 2.51 | 1.30 to 4.84 | 1.97 | 0.95 to 4.08 | 1.55 | 0.95 to 2.53 | 1.36 | 1.00 to 1.85 | 1.22 | 1.02 to 1.46 | 1.28 | 1.10 to 1.49 |
| Demographics: age, sex, smoking habit | 2.35 | 1.32 to 4.17 | 1.98 | 1.05 to 3.73 | 2.93 | 1.25 to 2.98 | 1.55 | 1.15 to 2.09 | 1.34 | 1.13 to 1.59 | 1.45 | 1.26 to 1.67 |
| Tumor burden: ECOG PS, weight loss, hemoglobin, albumin, alkaline phosphatase, calcium | 3.38 | 1.78 to 6.44 | 1.78 | 0.88 to 3.61 | 1.74 | 1.09 to 2.77 | 1.37 | 1.01 to 1.86 | 1.21 | 1.01 to 1.44 | 1.15 | 0.99 to 1.33 |
| Comorbidity: CCI score | 3.36 | 1.92 to 5.87 | 2.38 | 1.28 to 4.44 | 2.12 | 1.38 to 3.25 | 1.62 | 1.20 to 2.18 | 1.33 | 1.12 to 1.58 | 1.39 | 1.21 to 1.59 |
| Stage migration: PET | 3.54 | 2.02 to 6.19 | 2.14 | 1.16 to 3.95 | 1.86 | 1.22 to 2.84 | 1.64 | 1.22 to 2.20 | 1.37 | 1.16 to 1.63 | 1.37 | 1,19 to 1.57 |
| Tumor-related variables: histology, EGFR mutation, tumor size, N stage, No. of organs affected by metastasis | 3.44 | 1.96 to 6.03 | 2.36 | 1.22 to 4.55 | 2.41 | 1.57 to 3.70 | 1.98 | 1.44 to 2.73 | 1.23 | 1.03 to 1.47 | 1.61 | 1.39 to 1.87 |
| Treatment: no v yes* | 2.90 | 1.66 to 5.09 | 2.21 | 1.19 to 4.09 | 1.86 | 1.22 to 2.84 | 2.04 | 1.51 to 2.76 | 1.40 | 1.18 to 1.66 | 1.35 | 1.18 to 1.55 |
| Final fully adjusted model† | 2.07 | 1.06 to 4.05 | 2.24 | 1.02 to 4.94 | 1.62 | 0.95 to 2.94 | 1.57 | 1.08 to 2.28 | 1.16 | 0.98 to 1.39 | 1.45 | 1.22 to 1.71 |
NOTE. All HRs and 95% CIs were estimated by using patients with no PE in each stage as reference.
Abbreviations: CCI, Charlson comorbidity index; ECOG PS, Eastern Cooperative Oncology Group performance status; HR, hazard ratio; PE, pleural effusion; PET, positron emission tomography.
*First-line treatments for patients with stage I to IIIA: surgery alone, (neo) adjuvant chemotherapy, or concurrent (or sequential) chemoradiation; stage IIIB: concurrent (or sequential) chemoradiation or chemotherapy alone; stage IV: palliative chemotherapy or targeted therapy.
†The model included sex, age, smoking habit, CCI score, ECOG PS, weight loss, hemoglobin, albumin, alkaline phosphatase, calcium, histology, EGFR mutation, tumor size, N stage, No. of organs affected by metastasis, PET, and treatment.
Baseline characteristics according to PE status of the 2,061 patients in the study population are shown in Table 3. Median age of patients was 67.0 years, and there were 547 women (26.6%). According to histopathology, 48.7% of patients had an adenocarcinoma. Minimal PE presented in 272 patients (13.2%), and there was no PE in 1,397 (67.8%). Deaths were observed in 1,721 patients (83.5%). The proportion of patients presenting with minimal PE was seen to increase according to stage: 5.2% (20) in stage I, 10.9% (16) in stage II, 13.2% (30) in stage IIIA, 23.8% (59) in stage IIIB, and 13.9% (147) in stage IV (χ2 test P < .001). Patients with minimal PE had shorter survival compared with those with no PE (median survival time, 7.7 v 17.7 months, respectively; log-rank P < .001).
|
| Characteristic | Total (N = 2,061) | No PE (n = 1,397) | Minimal PE (n = 272) | Malignant PE (n = 392) | χ2 P | ||||
|---|---|---|---|---|---|---|---|---|---|
| No. | % | No. | % | No. | % | No. | % | ||
| Median age, years | 67.0 | 66.2 | 69.1 | 68.2 | |||||
| Sex | < .001 | ||||||||
| Male | 1,514 | 73.5 | 1,064 | 76.2 | 212 | 77.9 | 238 | 60.7 | |
| Female | 547 | 26.5 | 333 | 23.8 | 60 | 22.1 | 154 | 39.3 | |
| Smoking habit | < .001 | ||||||||
| Never | 459 | 22.7 | 282 | 20.6 | 50 | 18.5 | 127 | 33.4 | |
| Past | 576 | 28.5 | 390 | 28.5 | 87 | 32.2 | 99 | 26.1 | |
| Current | 983 | 48.8 | 696 | 50.9 | 133 | 49.3 | 154 | 40.5 | |
| CCI score | < .001 | ||||||||
| 0 | 683 | 33.3 | 493 | 35.5 | 69 | 25.5 | 121 | 30.9 | |
| 1 | 997 | 48.6 | 689 | 49.5 | 130 | 48.0 | 178 | 45.4 | |
| ≥ 2 | 373 | 18.2 | 208 | 15.0 | 72 | 26.5 | 93 | 23.7 | |
| ECOG PS | < .001 | ||||||||
| 0-1 | 1,272 | 66.5 | 959 | 75.6 | 145 | 54.9 | 168 | 44.2 | |
| ≥ 2 | 641 | 33.5 | 310 | 24.4 | 119 | 45.1 | 212 | 55.8 | |
| Weight loss, % | < .001 | ||||||||
| None to < 5 | 1,196 | 61.0 | 878 | 66.3 | 139 | 52.9 | 179 | 47.7 | |
| ≥ 5 | 766 | 39.0 | 446 | 33.7 | 124 | 47.1 | 196 | 52.3 | |
| Hemoglobin, g/dL* | < .001 | ||||||||
| ≥ 12 | 1,443 | 71.3 | 1,037 | 75.6 | 147 | 55.1 | 259 | 66.9 | |
| < 12 | 582 | 28.7 | 334 | 24.4 | 120 | 44.9 | 128 | 33.1 | |
| Albumin, g/dL* | < .001 | ||||||||
| ≥ 3.1 | 1,782 | 88.1 | 1,283 | 93.7 | 209 | 78.3 | 290 | 75.1 | |
| < 3.1 | 240 | 11.9 | 86 | 6.3 | 58 | 21.7 | 96 | 24.9 | |
| Alkaline phosphatase, IU/L* | .001 | ||||||||
| ≤ 335 | 1,761 | 87.2 | 1,219 | 89.2 | 223 | 83.5 | 319 | 82.6 | |
| > 335 | 259 | 12.8 | 148 | 10.8 | 44 | 16.5 | 67 | 17.4 | |
| Calcium, mg/dL* | .08 | ||||||||
| ≤ 10.8 | 1,976 | 97.9 | 1,345 | 98.3 | 257 | 96.3 | 374 | 97.4 | |
| > 10.8 | 43 | 2.1 | 23 | 1.7 | 10 | 3.7 | 10 | 2.6 | |
| PET | .007 | ||||||||
| No | 1,088 | 53.0 | 765 | 55.1 | 142 | 52.2 | 181 | 46.2 | |
| Yes | 965 | 47.0 | 624 | 44.9 | 130 | 47.8 | 211 | 53.8 | |
| Histology | < .001 | ||||||||
| ADC | 1,004 | 48.7 | 600 | 43.0 | 106 | 39.0 | 298 | 76.0 | |
| SQC | 863 | 41.9 | 653 | 46.7 | 139 | 51.1 | 71 | 18.1 | |
| Others | 194 | 9.4 | 144 | 10.3 | 27 | 9.9 | 23 | 5.9 | |
| EGFR mutation | .55 | ||||||||
| No | 314 | 15.2 | 222 | 15.9 | 39 | 14.3 | 53 | 13.5 | |
| Yes | 154 | 7.5 | 105 | 7.5 | 16 | 5.9 | 33 | 8.4 | |
| Not tested | 1,593 | 77.3 | 1,070 | 76.6 | 217 | 79.8 | 306 | 78.1 | |
| Stage† | < .001 | ||||||||
| I | 381 | 18.5 | 361 | 25.8 | 20 | 7.4 | 0 | ||
| II | 147 | 7.1 | 131 | 9.4 | 16 | 5.9 | 0 | ||
| IIIA | 227 | 11.0 | 197 | 14.1 | 30 | 11.0 | 0 | ||
| IIIB | 248 | 12.0 | 189 | 13.5 | 59 | 21.7 | 0 | ||
| IV | 1,058 | 51.3 | 519 | 37.2 | 147 | 54.0 | 392 | 100.0 | |
| T stage | < .001 | ||||||||
| Tx | 8 | 0.4 | 5 | 0.4 | 1 | 0.4 | 2 | 0.5 | |
| T1 | 231 | 11.3 | 213 | 15.3 | 11 | 4.1 | 7 | 1.8 | |
| T2 | 638 | 31.2 | 548 | 39.4 | 65 | 24.0 | 25 | 6.5 | |
| T3 | 330 | 16.1 | 258 | 18.6 | 43 | 15.8 | 29 | 7.5 | |
| T4 | 840 | 41.0 | 366 | 26.3 | 151 | 55.7 | 323 | 83.7 | |
| Tumor size, cm | < .001 | ||||||||
| 0-3 | 445 | 21.6 | 351 | 25.1 | 31 | 11.4 | 63 | 16.1 | |
| 3.1-5 | 713 | 34.6 | 524 | 37.5 | 89 | 32.7 | 100 | 25.5 | |
| 5.1-7 | 424 | 20.6 | 281 | 20.1 | 78 | 28.7 | 65 | 16.6 | |
| 7.1-16 | 248 | 12.0 | 130 | 9.3 | 58 | 21.3 | 60 | 15.3 | |
| Unmeasurable | 231 | 11.2 | 111 | 7.9 | 16 | 5.9 | 104 | 26.5 | |
| N stage | < .001 | ||||||||
| N0 | 742 | 36.4 | 585 | 42.1 | 64 | 23.9 | 93 | 24.2 | |
| N1 | 190 | 9.3 | 155 | 11.2 | 23 | 8.6 | 12 | 3.1 | |
| N2 | 505 | 2.7 | 330 | 23.7 | 86 | 32.1 | 89 | 23.1 | |
| N3 | 605 | 29.6 | 319 | 23.0 | 95 | 35.4 | 191 | 49.6 | |
| M stage | < .001 | ||||||||
| M0 | 1,003 | 48.7 | 878 | 62.9 | 123 | 45.5 | 0 | ||
| M1a | 399 | 19.3 | 158 | 11.3 | 41 | 15.2 | 200 | 51.0 | |
| M1b | 659 | 32.0 | 361 | 25.8 | 106 | 39.3 | 192 | 49.0 | |
| No. of organs affected by metastasis | < .001 | ||||||||
| 0 | 1,402 | 68.0 | 1,036 | 74.2 | 166 | 61.0 | 200 | 51.0 | |
| 1 | 376 | 18.2 | 218 | 15.6 | 56 | 20.6 | 102 | 26.0 | |
| 2 | 181 | 8.8 | 99 | 7.1 | 29 | 10.7 | 53 | 13.5 | |
| ≥ 3 | 102 | 5.0 | 44 | 3.1 | 21 | 7.7 | 37 | 9.5 | |
| Treatment | < .001 | ||||||||
| No | 900 | 43.7 | 561 | 40.2 | 143 | 52.6 | 196 | 50.0 | |
| Yes‡ | 1,161 | 56.3 | 836 | 59.8 | 129 | 47.4 | 196 | 50.0 | |
| Survival | < .001 | ||||||||
| Alive | 340 | 16.5 | 313 | 22.4 | 18 | 6.6 | 9 | 2.3 | |
| Death | 1,721 | 83.5 | 1,084 | 77.6 | 254 | 93.4 | 383 | 97.7 | |
Abbreviations: ADC, adenocarcinoma; CCI, Charlson comorbidity index; ECOG PS, Eastern Cooperative Oncology Group performance status; PE, pleural effusion; PET, positron emission tomography; SQC, squamous cell carcinoma.
*Dichotomized by cutoff of normal value.
†Clinical stage at the time of initial diagnosis was determined according to seventh edition of the TNM classification.
‡First-line treatments for patients with stage I to IIIA: surgery alone, (neo) adjuvant chemotherapy, or concurrent (or sequential) chemoradiation; stage IIIB: concurrent (or sequential) chemoradiation or chemotherapy alone; stage IV: palliative chemotherapy or targeted therapy.
Distribution of the variables between no PE and minimal PE groups indicates no differences among sex, smoking habit, histology, EGFR mutation, or use of PET scans. However, lower CCI score; better ECOG PS (0 to 1); absence of weight loss; normal levels of hemoglobin, albumin, and alkaline phosphatase; smaller tumor size; low N stage; small number of organs affected by metastasis; and curative treatment were more likely in the no PE group (χ2 test P < .001). All variables related to patient, stage migration, tumor, and treatment exerted significant effects on overall survival (Appendix Table A2, online only).
There were 270 patients with minimal PE in which a cause of accumulation was found during data review. Of these, 237 (87.8%) had a direct mechanism of invasion or attachment to pleura by tumor (Fig 2). For indirect mechanisms, 183 patients (67.8%) had tumor involvement with the mediastinal lymph nodes. Other mechanisms were observed in 18 patients (6.7%): pneumonia (10) and uncontrolled heart (4), kidney (3), and liver (1) diseases. Both direct and indirect mechanisms were found in 177 patients (65.5%). No difference was found in survival according to laterality of minimal PE (log-rank P = .63). Patients with direct mechanism had worse overall survival than patients without direct mechanism, when adjusted with all the variables (adjusted HR, 1.75; 95% CI, 1.06 to 2.91; Appendix Table A3, online only). Among patients with minimal PE, involvement with the mediastinal lymph nodes, heart and major vessels, or two or more numbers of causes tended to indicate worse survival, but differences were not significant.
Fig 2. Mechanisms involved in the accumulation of minimal pleural effusion by (A) causes, (B) direct and indirect mechanisms, and (C) number of causes (n = 270).
Patients with minimal PE showed significantly worse survival than those with no PE (unadjusted HR, 2.33; 95% CI, 2.04 to 2.65; Table 1 and Fig 3). Presence of minimal PE was a consistent and significant factor for predicting worse overall survival at every step of the analysis when adjusted in a stepwise fashion, with each group of variables related to patient, stage migration, tumor, or treatment. In the final fully adjusted model, presence of minimal PE was an independent prognostic factor of worse survival when compared with the no PE group (adjusted HR, 1.40; 95% CI, 1.22 to 1.62; P < .001). The Harrell's c-index was 0.77 (95% CI, 0.75 to 0.78) for assessing accuracy of the final model.
Fig 3. Overall survival of the total study population by (A) status of pleural effusion (PE) and by disease stage and status of pleural effusion at (B) stage I, (C) stage II, (D) stage IIIA, (E) stage IIIB, and (F) stage IV. MST, median survival time.
From analysis of the impact of minimal PE on survival by stages, association of minimal PE with risk of death increased as a function of decrease in stage, from stages IV through I (adjusted HRs: 2.07 for stage I, 2.24 for stage II, 1.62 for stage IIIA, 1.57 for stage IIIB, and 1.16 for stage IV; Table 2). Effect of modification of PE status according to disease stage and its relationship to survival was analyzed, revealing that the impact of minimal PE was stronger in early-stage disease (Pinteraction = .001). When stage I with no PE was used as reference group in estimating risk of death, stage I with minimal PE showed higher risk compared with stage IIIA with no PE (adjusted HRs were 2.97 and 2.60, respectively; Appendix Table A4, online only). In patients with stage IV disease, risk of death increased with change of PE status (from no PE through malignant PE; adjusted HR, 1.20; 95% CI, 1.11 to 1.31; Ptrend < .001). When divided into M1a and M1b subgroups, this trend was maintained (Appendix Table A5, online only; Appendix Fig A1, online only).
For patients with malignant PE, there were no differences in overall survival between patients with or without pleural malignant cells, pleural nodules, or no diagnostic work-up (P = .18; data not shown).
In this study, we report that minimal PE usually presents at diagnosis and is an independent prognostic factor of worse survival among patients with NSCLC.
Although there have been no epidemiologic studies, previous studies have reported that malignant PE is present in 11% to 32% of patients with advanced NSCLC.5–8 However, no study has reported the proportion of patients with minimal PE in which thoracentesis and/or pleural biopsy was not recommended. In this study, we found that 13.2% of patients with NSCLC in the study population present with minimal PE. This high proportion may be due to the meticulous attention paid to detecting minimal PE in this study, but it also agrees with a recent increasing trend toward adenocarcinoma (48.7% in this study). The presence of minimal PE should be of concern regarding delayed and inaccurate staging of the disease or with respect to morbidity or mortality related to more invasive approaches.
There are several explanations for PE accumulation.9–12 Postmortem studies have suggested that tumor involvement of mediastinal lymph nodes is essential for PE accumulation.10,13 By contrast, Light et al12 claimed that this hypothesis does not fully explain exudative PE or the presence of malignant cells in most cases of malignant PE, and they postulated direct invasion of pleura as the primary reason, or in combination with indirect mechanisms. Direct mechanism was seen in 87% of patients with minimal PE and both direct and indirect mechanisms in 65%. These findings suggest that minimal PE represents an early phase in the development of malignant PE and support the combination hypothesis.12 In addition, minimal PE also occurs in severe comorbid diseases. The CCI score is a validated method for evaluating individual comorbidity and is well known to have an effect on treatment decision and survival of patients with NSCLC.14–16 Patients with minimal PE had higher CCI score compared with those in the no PE group in this study. When minimal PE represented an early phase of malignant PE or had developed as a result of severe comorbid diseases, it is reasonable to assume that these could impair survival.
In this study, 17 variables related to patient, stage migration, tumor, and treatment were considered as potential confounders. It is important to know whether consistency of the impact of minimal PE was maintained at each step in the stepwise analysis of adjusting for each group of variables. We demonstrated that having minimal PE was consistently predictive of worse survival, and the minimal PE group showed a 40% increase in risk of death when compared with the no PE group. The prognostic impact of minimal PE can be deduced from a recent meta-analysis. Lim et al17 reported that pleural lavage cytology positive for tumor cells during surgical resection is an independent factor in predicting worse survival of patients with a resectable-stage tumor.
We also found that the effect of minimal PE on survival varies according to disease stage, with greatest effect in early disease. This indicates that the impact could be maximized in patients with early-stage disease through tumor stage shifting. However, as expected, the proportion of patients with minimal PE was lower in early-stage disease compared with advanced stage disease.
As PE status changed from no PE through malignant PE in patients with stage IV disease, risk of death in minimal or malignant PE gradually increased. Patients with malignant PE had larger amounts of effusion, and this could have had a prognostic impact. This is supported by a recent study in patients with advanced-stage ovarian carcinomas, demonstrating that a moderate-to-large PE is an independent prognostic factor for predicting worse survival when compared with a small PE.18 In addition, there is evidence that increased tumor burden within the pleural space is associated with worse survival among patients with malignant PE.19,20
This study has several limitations. First, environmental factors, such as education level, socioeconomic status, access to care, insurance status, and quality of treatment or diagnosis, could be important and should be considered in identifying more robust prognostic markers.21,22 Unfortunately, most of these factors could not be considered in this study because it was based on a cohort of patients with lung cancer that did not include such environmentally related items. However, factors related to host, tumor, and treatment were considered in detail in this study. Second, our study population was enrolled over 9 years. Therefore, advances in treatment or supportive care and the possibility of stage migration by PET could have been subject to selection bias in analyzing prognostic effects. However, enrollment was limited to patients staged with contrast-enhanced chest CT scans, bone scans, and brain imaging to maintain homogeneity of the population. Interestingly, we found no difference in stage-specific survival based on whether PET was used or not (data not shown). Third, the natural course of minimal PE should be valuable in understanding its nature and significance. However, strict follow-ups with chest CT scan or pleural fluid analysis, when fluid had increased in amount, were not attempted aggressively in this study. This was largely because the study design was retrospective in nature and partially because of the shorter survival of patients: 43% of the patients received either no treatment or palliative treatment alone. Treatment response, treatment-related untoward effects, comorbid diseases, or pattern of tumor progression can also complicate the natural course of disease. In our study, we paid meticulous attention to evaluating the mechanism of pleural fluid accumulation through reviewing chest CT scans, bronchoscopic examinations, and laboratory data and noting comorbid diseases at diagnosis. Finally, validation is needed in another data set before conclusions from this study can be considered as a subset of TNM stage criteria. Nevertheless, this is a systematic study examining the proportion of patients with minimal PE, the mechanisms involved in PE accumulation, and its prognostic impact among patients with cancer.
Supported by Grant No. A110518 from the Korea Healthcare Technology R&D Project, Ministry for Health, Welfare & Family Affairs, Republic of Korea.
Authors' disclosures of potential conflicts of interest and author contributions are found at the end of this article.
The author(s) indicated no potential conflicts of interest.
Conception and design: Jeong-Seon Ryu, Hyo Jin Ryu
Financial support: Jeong-Seon Ryu
Administrative support: Jeong-Seon Ryu, Azra Memon, Seul-Ki Lee, Hyun-Jung Kim
Provision of study materials or patients: Jeong-Seon Ryu, Hyun-Jung Kim
Collection and assembly of data: Jeong-Seon Ryu, Hyo Jin Ryu, Si-Nae Lee, Seul-Ki Lee, Hae-Seong Nam, Hyun-Jung Kim, Jae-Hwa Cho
Data analysis and interpretation: Jeong-Seon Ryu, Azra Memon, Kyung-Hee Lee, Seung-Sik Hwang
Manuscript writing: All authors
Final approval of manuscript: All authors
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Acknowledgment
The corresponding author thanks Bong Wan Noh, MD; Jun Hyeok Lim, MD; Jung Min Lee, MD; and Gwang Seok Yoon, MD, for their generous support and cooperation.
|
| Mechanism | Classification |
|---|---|
| Direct | Tumor invasion or broad attachment to pleura |
| Indirect | Tumor involvement of mediastinal lymph node |
| Complete obstruction in one or more lobar or main bronchus or atelectasis in more than one lobe | |
| Significant tumor infiltration or compression to heart or major vessels (superior vena cava, main trunk of pulmonary artery or vein) or significant pulmonary thromboembolism | |
| Lymphangitic metastasis to more than one lobe | |
| Other | Pneumonia |
| Uncontrolled heart, kidney, thyroid and liver disease |
Abbreviation: PE, pleural effusion.
|
| Variable | MST (months) | 95% CI | HR | 95% CI |
|---|---|---|---|---|
| PE | ||||
| No | 17.7 | 16.0 to 19.4 | 1 | |
| Minimal | 7.7 | 6.4 to 9.0 | 2.32 | 2.04 to 2.65 |
| Malignant | 5.5 | 4.3 to 6.7 | 2.80 | 2.48 to 3.17 |
| Age per year | 1.03 | 1.03 to 1.04 | ||
| Sex | ||||
| Male | 11.1 | 10.1 to 12.1 | 1 | |
| Female | 17.6 | 15.2 to 20.0 | 0.77 | 0.69 to 0.86 |
| Smoking habit | ||||
| Never | 19.4 | 16.7 to 22.2 | 1 | |
| Past | 10.6 | 9.1 to 12.2 | 1.43 | 1.25 to 1.64 |
| Current | 11.6 | 10.4 to 12.7 | 1.34 | 1.18 to 1.52 |
| CCI score | ||||
| 0 | 16.5 | 13.9 to 19.1 | 1 | |
| 1 | 13.0 | 11.7 to 14.2 | 1.24 | 1.11 to 1.38 |
| ≥ 2 | 6.8 | 5.7 to 8.0 | 2.02 | 1.76 to 2.31 |
| ECOG PS | ||||
| 0-1 | 17.4 | 15.8 to 19.1 | 1 | |
| ≥ 2 | 5.9 | 5.0 to 6.7 | 2.46 | 2.22 to 2.74 |
| Weight loss, % | ||||
| None to < 5 | 17.4 | 15.7 to 19.1 | 1 | 1.67 to 2.04 |
| ≥ 5 | 7.9 | 7.1 to 8.6 | 1.85 | |
| Hemoglobin, g/dL* | ||||
| ≥ 12 | 14.8 | 13.6 to 15.9 | 1 | 1.40 to 1.72 |
| < 12 | 7.8 | 6.7 to 8.8 | 1.55 | |
| Albumin, g/dL* | ||||
| ≥ 3.1 | 14.3 | 13.3 to 15.3 | 1 | |
| < 3.1 | 3.9 | 2.7 to 5.2 | 2.47 | 2.15 to 2.85 |
| Alkaline phosphatase, IU/L* | ||||
| ≤ 335 | 13.3 | 12.3 to 14.4 | 1 | |
| > 335 | 6.5 | 5.0 to 7.9 | 1.64 | 1.42 to 1.89 |
| Calcium, mg/dL* | ||||
| ≤ 10.8 | 12.7 | 11.7 to 13.6 | 1 | |
| > 10.8 | 2.7 | 0.1 to 5.3 | 2.65 | 1.94 to 3.62 |
| PET | ||||
| Yes | 14.4 | 12.9 to 15.8 | 1 | |
| No | 10.9 | 9.8 to 12.1 | 1.20 | 1.10 to 1.33 |
| Histology | ||||
| SQC | 12.0 | 10.7 to 13.4 | 1 | |
| ADC | 14.3 | 13.0 to 15.7 | 0.98 | 0.89 to 1.09 |
| Others | 7.9 | 5.5 to 10.4 | 1.23 | 1.04 to 1.46 |
| EGFR mutation | ||||
| Yes | 21.9 | 14.8 to 29.0 | 1 | |
| No | 11.7 | 9.8 to 13.6 | 1.40 | 1.12 to 1,75 |
| Not tested | 12.2 | 11.0 to 13.3 | 1.31 | 1.08 to 1.59 |
| Stage† | ||||
| I | 75.5 | 59.3 to 91.7 | 1 | |
| II | 25.1 | 20.9 to 29.3 | 2.07 | 1.59 to 2.68 |
| IIIA | 16.8 | 14.3 to 19.2 | 3.45 | 2.79 to 4.27 |
| IIIB | 12.2 | 10.2 to 14.3 | 5.23 | 4.27 to 6.42 |
| IV | 6.8 | 6.1 to 7.6 | 7.64 | 6.42 to 9.10 |
| Tumor size, cm | ||||
| 0-3 | 29.0 | 25.3 to 32.8 | 1 | |
| 3.1-5 | 14.5 | 12.8 to 16.2 | 1.73 | 1.50 to 1.99 |
| 5.1-7 | 8.8 | 7.5 to 10.0 | 2.67 | 2.29 to 3.12 |
| 7.1-16 | 5.6 | 3.9 to 7.3 | 3.24 | 2.72 to 3.86 |
| Unmeasurable | 9.2 | 7.1 to 11.4 | 2.59 | 2.17 to 3.09 |
| N stage | ||||
| N0 | 27.7 | 24.3 to 31.1 | 1 | |
| N1 | 16.7 | 13.1 to 20.2 | 1.41 | 1.18 to 1.69 |
| N2 | 10.1 | 8.7 to 11.5 | 2.45 | 2.16 to 2.79 |
| N3 | 6.1 | 5.3 to 6.8 | 3.87 | 3.41 to 4.39 |
| No. of organs affected by metastasis | ||||
| 0 | 17.6 | 16.0 to 19.2 | 1 | |
| 1 | 6.8 | 5.6 to 8.1 | 2.38 | 2.11 to 2.68 |
| 2 | 5.0 | 3.7 to 6.3 | 2.89 | 2.46 to 3.41 |
| ≥ 3 | 2.7 | 2.0 to 3.4 | 4.15 | 3.37 to 5.12 |
| Treatment | ||||
| No | 7.0 | 6.1 to 7.9 | 1 | |
| Yes | 17.0 | 15.4 to 18.7 | 0.53 | 0.48 to 0.58 |
Abbreviations: ADC, adenocarcinoma; CCI, Charlson comorbidity index; ECOG PS, Eastern Cooperative Oncology Group performance status; HR, hazard ratio; MST, median survival time; PE, pleural effusion; PET, positron emission tomography; SQC, squamous cell carcinoma.
*Dichotomized by cutoff point of normal value.
†Clinical stage at the time of initial diagnosis was determined according to the seventh edition of the TNM classification.
|
| Mechanism | MST (months) | 95% CI | Log-Rank P | aHR* | 95% CI | Cox P |
|---|---|---|---|---|---|---|
| Direct | ||||||
| Pleura | ||||||
| Yes | 7.4 | 6.1 to 8.8 | .06 | 1 | ||
| No | 10.4 | 3.1 to 17.7 | 1.75 | 1.06 to 2.91 | .03 | |
| Indirect | 1 | |||||
| Mediastinum | ||||||
| Yes | 6.7 | 5.2 to 8.3 | < .01 | 1.47 | 0.41 to 5.19 | .55 |
| No | 9.5 | 6.5 to 12.5 | 1 | — | ||
| Obstruction | ||||||
| Yes | 7.4 | 4.5 to 10.4 | .61 | 0.88 | 0.61 to 1.27 | .48 |
| No | 7.6 | 5.8 to 9.4 | — | — | — | |
| Heart, major vessels | ||||||
| Yes | 5.4 | 3.1 to 7.8 | < .01 | 1 | — | — |
| No | 8.0 | 6.4 to 9.5 | 1.18 | 0.73 to 1.91 | .49 | |
| Lymphangitic metastasis | ||||||
| Yes | 7.7 | 4.4 to 11.1 | .62 | 1 | — | — |
| No | 7.5 | 5.8 to 9.2 | 1.67 | 0.90 to 3.10 | .10 | |
| No. of causes | ||||||
| 1 | 10.4 | 6.2 to 14.5 | < .01 | 1 | ||
| ≥ 2 | 6.7 | 5.2 to 8.3 | 1.46 | 0.89 to 2.40 | .14 |
Abbreviations: aHR, adjusted hazard ratio; HR, hazard ratio; MST, median survival time; PE, pleural effusion.
*HR after adjustment with sex, age, smoking habit, Charlson comorbidity index score, Eastern Cooperative Oncology Group performance status, weight loss, hemoglobin, albumin, alkaline phosphatase, calcium, histology, epidermal growth factor receptor mutation, tumor size, N stage, No. of organs affected by metastasis, positron emission tomography, and treatment.
|
| Stage | No PE | Minimal PE | ||
|---|---|---|---|---|
| HR | 95% CI | HR | 95% CI | |
| I | 1.00 (reference) | 2.97 | 1.65 to 5.35 | |
| II | 1.54 | 1.11 to 2.14 | 2.70 | 1.46 to 5.01 |
| IIIA | 2.60 | 1.89 to 3.59 | 3.92 | 2.41 to 6.38 |
| IIIB | 3.53 | 2.64 to 4.72 | 5.52 | 3.80 to 8.02 |
| IV | 5.14 | 3.85 to 6.79 | 5.55 | 4.02 to 7.65 |
NOTE. HRs were estimated after adjustment with sex, age, smoking habit, Charlson comorbidity index score, Eastern Cooperative Oncology Group performance status, weight loss, hemoglobin, albumin, alkaline phosphatase, calcium, histology, epidermal growth factor receptor mutation, positron emission tomography, and treatment.
Abbreviations: HR, hazard ratio; PE, pleural effusion.
|
| Variable | Stage IV M1a | Stage IV M1b | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| No PE (ref) | Minimal PE | Malignant PE | Ptrend | No PE (ref) | Minimal PE | Malignant PE | Ptrend | |||||
| HR | 95% CI | HR | 95% CI | HR | 95% CI | HR | 95% CI | |||||
| Unadjusted | 1 | 1.54 | 1.13 to 2.10 | 1.47 | 1.18 to 1.82 | .001 | 1 | 1.31 | 1.07 to 1.61 | 1.50 | 1.25 to 1.80 | < .001 |
| Patient-related variables | 1 | 1.30 | 0.93 to 1.82 | 1.36 | 1.06 to 1.73 | .019 | 1 | 1.21 | 0.97 to 1.50 | 1.46 | 1.19 to 1.80 | < .001 |
| Demographics: age, sex, smoking habit | 1 | 1.58 | 1.15 to 2.16 | 1.56 | 1.24 to 1.95 | < .001 | 1 | 1.26 | 1.02 to 1.55 | 1.68 | 1.39 to 2.03 | < .001 |
| Tumor burden: ECOG PS, weight loss, hemoglobin, albumin, alkaline phosphatase, calcium | 1 | 1.26 | 0.91 to 1.75 | 1.18 | 0.94 to 1.50 | .170 | 1 | 1.20 | 0.97 to 1.49 | 1.25 | 1.03 to 1.53 | .020 |
| Comorbidity: CCI score | 1 | 1.51 | 1.11 to 2.06 | 1.53 | 1.23 to 1.91 | < .001 | 1 | 1.25 | 1.02 to 1.54 | 1.50 | 1.25 to 1.80 | < .001 |
| Stage migration: PET | 1 | 1.52 | 1.12 to 2.07 | 1.32 | 1.07 to 1.62 | .001 | 1 | 1.32 | 1.07 to 1.62 | 1.50 | 1.25 to 1.80 | < .001 |
| Tumor-related variables: histology, EGFR mutation, tumor size N stage, No. of organs affected by metastasis | 1 | 1.45 | 1.06 to 1.98 | 1.64 | 1.30 to 2.06 | < .001 | 1 | 1.20 | 0.97 to 1.48 | 1.33 | 1.10 to 1.62 | < .001 |
| Treatment: no v yes* | 1 | 1.53 | 1.12 to 2.09 | 1.47 | 1.18 to 1.83 | .001 | 1 | 1.36 | 1.11 to 1.68 | 1.48 | 1.23 to 1.78 | < .001 |
| Final fully adjusted model† | 1 | 1.33 | 0.92 to 1.91 | 1.66 | 1.26 to 2.20 | < .001 | 1 | 1.11 | 0.90 to 2.03 | 1.44 | 1.15 to 1.79 | .002 |
NOTE. All HRs and 95% CIs were estimated by using patients without PE in each stage as ref.
Abbreviations: CCI, Charlson comorbidity index; ECOG PS, Eastern Cooperative Oncology Group performance status; HR, hazard ratio; PE, pleural effusion; PET, positron emission tomography; ref, reference.
*First-line treatments for patients with stage I to IIIA: surgery alone, (neo) adjuvant chemotherapy, or concurrent (or sequential) chemoradiation; stage IIIB: concurrent (or sequential) chemoradiation or chemotherapy alone; stage IV: palliative chemotherapy or targeted therapy.
†The model included sex, age, smoking habit, CCI score, ECOG PS, weight loss, hemoglobin, albumin, alkaline phosphatase, calcium, histology, EGFR mutation, tumor size, N stage, No. of organs affected by metastasis, PET, and treatment.
Fig A1. Overall survival and status of pleural effusion (PE) within subgroups of stage IV: (A) M1a and (B) M1b. MST, median survival time.
