Beginning in 2008, and then as a formal initiative in 2010, we, as members of the British Columbia Ovarian Cancer Research Team (OVCARE) that is based in Vancouver, have suggested to gynecologic surgeons that they should consider the following: perform bilateral salpingectomy in all women at the time of hysterectomy (even when the ovaries are being preserved) and perform bilateral salpingectomy in place of tubal ligation for sterilization. In September 2010, we circulated a DVD to all gynecologic surgeons in British Columbia, which included a review of the rationale for salpingectomy. This initiative has had a profound effect on clinical practice in British Columbia: the proportion of hysterectomies that had associated salpingectomies (excluding hysterectomies in which ovaries were removed, the rate of which remains unchanged) increased from 8% in 2008 to 63% in 2011 and to 75% in 2013, and the proportion of sterilizations by bilateral salpingectomy increased from 0.5% in 2008 to 33% in 2011 and to 48% in 2013.¹⁸ The Society of Gynecologic Oncologists of Canada, U.S. Society for Gynecologic Oncology, American College of Obstetrics and Gynecology, and Royal Australian and New Zealand College of Obstetricians and Gynecologists have all since published statements that recommend consideration of salpingectomy for all women at the time of gynecologic surgery,^19-22 and physician surveys show willingness to undertake practice change.^23-26 It is essential to clarify that this campaign is aimed at women in the general (low-risk) population who have a lifetime risk of developing ovarian cancer of approximately 1.7%; importantly, risk-reducing bilateral salpingo-oophorectomy at age 40 or after completion of childbearing²⁷ is still recommended and represents the standard of care in high-risk populations, such as in BRCA1/2-mutation carriers. A two-step procedure of risk-reducing salpingectomy followed by oophorectomy in high-risk women, although feasible, carries increased surgical risks, and there is insufficient data to support optimal timing or protective effect (if any) for breast and ovarian cancers; thus, the two-step procedure is reserved for women who are unwilling to undergo risk-reducing bilateral salpingo-oophorectomy.^28,29

We have termed this intervention in the low-risk population opportunistic salpingectomy, which suggests that surgeons should take the opportunity to remove the fallopian tubes if there is access to these anatomic structures during other scheduled gynecologic procedures but should not perform a procedure solely for the purpose of tubal removal for ovarian cancer prevention. We have published data from a time period 2 years prior and 2 years after the formal introduction of this campaign, including data from procedures performed on 43,931 women. We observed no increase in major perioperative complications or events. Blood loss, length of hospital stay, and readmission rates were the same in patients who underwent opportunistic salpingectomy and in patients who underwent hysterectomy alone or tubal ligation procedures.¹⁸ Potential long-term hormonal consequences of opportunistic salpingectomy have been investigated through measurement of ovarian sonographic parameters and hormonal assays; data are reassuring but have relatively short follow-up.^30-32 Given that an earlier age at menopause has been associated with increased mortality, it is imperative that this does not offset any projected protective effect in ovarian cancer risk reduction. Hysterectomy is known to affect ovarian reserve^33,34 and the relative impact of opportunistic salpingectomy performed with hysterectomy is likely small or immeasurable. To answer this definitively we are studying our British Columbia cohort of women who have undergone these procedures, comparing onset of menopause (defined as cessation of menses for 1 year) in individuals who have undergone bilateral salpingectomy versus tubal ligation for permanent sterilization. In addition, there is a planned randomized clinical trial in the United Kingdom in women who will undergo bilateral salpingectomy either at hysterectomy or as a stand-alone procedure for contraception.³⁵

Is the increased uptake of opportunistic salpingectomy responsible in terms of use of resources and health economics? Our group and others have shown that this procedure can be undertaken by different surgical routes (vaginal, minimally invasive, laparotomy)^18,36-38 so it does not need to be limited to high-resource countries. Additional operating room time needed for opportunistic salpingectomy with hysterectomy is approximately 16 minutes, and, in lieu of tubal ligation, the procedure requires approximately 10 minutes,¹⁸ a time that arguably is of no clinical impact to the majority of women undergoing these procedures nor to the health systems where the procedures are being performed. Cost analysis modeling, which considers perioperative risks, impact on ovarian cancer risk reduction, and morbidities associated with premature menopause secondary to oophorectomy, found that opportunistic salpingectomy with hysterectomy was less costly and more effective than hysterectomy alone, reduced the number of ovarian cancer occurrences, and prolonged the average life expectancy. Opportunistic salpingectomy for sterilization would be considered more costly than tubal ligation in terms of operative time and complication risk; however, opportunistic salpingectomy was more effective at reducing risk of ovarian cancer. The calculated number needed to treat to prevent a single occurrence of ovarian cancer was acceptable for both procedures.³⁹

Finally, and most importantly, will this change in surgical paradigm translate to a decreased incidence of ovarian cancer? Proof of success of this initiative will be an observed reduction in new occurrences of ovarian cancer, and we anticipate there will be a shift in the distribution of histotypes of epithelial ovarian cancer in the population of women exposed to this procedure. The age of women undergoing this procedure as part of hysterectomy or for permanent sterilization is younger than the age of onset of ovarian cancer in the general population, so we anticipate that it will be at least 10 years and up to 20 years from the start of our campaign before we will be able to discern a difference that would provide definitive support for this intervention. Pooling of our data with data from other geographic areas that have adopted this practice may help power the analysis and hasten results. Although nay-sayers may be frustrated or unsatisfied with this lack of immediate measurable impact, we hold to this long view and are very encouraged by emerging evidence from other historical cohorts that supports this intervention. In addition to the strong protective effect demonstrated in women who have undergone tubal ligation (outlined previously), there are data from a small number of studies on women who have undergone excisional tubal surgery (defined as complete salpingectomy, distal fimbriectomy, or partial salpingectomy). Researchers from the Rochester Epidemiology Project reported a 64% reduction in the risk of ovarian cancer after excisional tubal sterilization compared with those without sterilization or with nonexcisional tubal sterilization (odds ratio [OR] 0.36; 95% CI, 0.13–1.02).⁴⁰ Danish researchers, who used a national database, reported that bilateral salpingectomy reduced risk for ovarian cancer by 42% (OR 0.58; 95% CI, 0.36–0.95).⁴¹ Most recently, a retrospective population-based study that used Swedish health registers reported that bilateral salpingectomy was associated with a 65% reduction in risk (hazard ratio 0.35; 95% CI, 0.17–0.73).⁴² Both the Danish and Swedish studies examined retrospective data and included women who underwent salpingectomies for pathologic reasons (e.g., hydrosalpinx, pelvic inflammatory disease, ectopic pregnancy), which makes them significantly different from the women undergoing opportunistic salpingectomy in British Columbia for the purposes of ovarian cancer prophylaxis. We hypothesize that salpingectomy performed for risk-reduction purposes may confer more protection than those performed for other indications, because surgeons will be more careful to remove the entire distal end of the fallopian tube.

Published data reassure us of the safety of the procedure and suggest that opportunistic salpingectomy should be easily within the skill set of any pelvic/abdominal surgeon and can be performed by multiple surgical routes; there is health economic support, and the evidence of high uptake suggests feasibility. In addition, there are numerous nononcologic arguments for tubal removal, including prevention of hydrosalpinges, pyosalpinx, or tubal prolapse that may require subsequent surgeries.⁴³ However, as we wait to definitively measure the impact of this procedure on ovarian cancer risk, whether a woman undergoes opportunistic salpingectomy will remain a decision between her and her treating physician, and the decision requires good judgment and common sense. Our first dictum as physicians is to do no harm.

The standard strategy for advanced epithelial ovarian cancer remains the combination of surgery and platinum/taxane-based chemotherapy,⁴⁴ which is primarily driven by activity in unselected populations enrolled in clinical trials; the populations are predominantly composed of women with high-grade serous ovarian cancer. One of five histologic subtypes of epithelial ovarian cancer, low-grade serous ovarian cancer is a rare subentity with a specific genomic landscape, as evidenced by a different natural history and pattern of response to therapy.⁴⁵ From available evidence, low-grade serous ovarian cancer may arise after an initial diagnosis of serous tumor of low malignant potential (Fig. 2) or de novo and does not seem to be part of the hereditary breast-ovarian cancer syndrome related to the BRCA1/2 gene mutation.⁴⁶

FIGURE 2. Carcinogenesis Pathway in Low-Grade Serous Ovarian Cancer

Pictures courtesy of Dr. Patricia A. Shaw, University Health Network of Toronto.

The dogma of cytotoxic chemotherapy for all epithelial ovarian cancers is evolving on the basis of the recent clinical and molecular classification of the different subtypes of epithelial ovarian cancer.⁴⁷ To date, no prospective randomized clinical trial data are available to provide guidance about the optimal postoperative treatment of low-grade serous ovarian cancer.⁴⁸ Although available data are mostly based on small retrospective, single-institution studies, chemotherapy resistance is consistently reported in low-grade serous ovarian cancer.^48,49 From a single-institution database, 112 women with stages II to IV low-grade serous ovarian cancer who underwent primary surgery followed by platinum-based chemotherapy were retrospectively identified. Of these, 42 patients underwent second-look surgery, and 2, 13, and 24 had evidence of no residual disease, microscopically positive disease, or macroscopically positive disease, respectively.⁵⁰ Similar findings were reported with low-grade primary peritoneal cancer, with high rates of persistent disease at the completion of adjuvant chemotherapy.⁵¹ This relative chemotherapy resistance, possibly related to the nature of low-grade serous ovarian cancer, was also observed in a separate retrospective study that included patients treated with neoadjuvant chemotherapy.⁵² Despite the receipt of a taxane and platinum combination in the majority of the 25 patients with advanced low-grade serous ovarian cancer, only one patient had a complete response (CR); an additional 21 women had stable disease, but two experienced progression after neoadjuvant chemotherapy. Although CA-125 levels were reduced by greater than 50% with chemotherapy in half of the patients, radiologic response remained low.

Chemotherapy resistance also has been demonstrated in the setting of recurrent disease. For example, in a retrospective study of 58 women with recurrent low-grade serous ovarian cancer who received 108 separate chemotherapy regimens,⁴⁹ only four responses were seen (one CR and three partial responses; overall response rate [ORR], 3.7%). The ORR was 4.9% for the platinum-sensitive cohort and 2.1% for the platinum-resistant cohort. Stable disease that was observed in 65 (60.2%) of 108 chemotherapy regimens may have been related to tumor biology or may have been a bias of assessment—measureable lesions can often appear stable by RECIST criteria on CT scans⁵³—and not a true therapeutic effect. As such, given the relative chemotherapy resistance, we should consider making clinical trials the new standard. Targeted biologically directed therapy is an interesting area of investigation in low-grade serous ovarian cancer, given the molecular characteristics of disease. Compared with high-grade serous ovarian cancer, low-grade serous ovarian cancer has lower expression of p53, WT1, c-KIT, Ki-67, and MMP-9⁵⁴ but a higher expression of estrogen receptor, progesterone receptor, and E-cadherin.⁵⁵

Low-grade serous ovarian cancer often is diagnosed at a younger age (43 to 55 years), so a higher proportion of patients with low-grade serous ovarian cancer are premenopausal at diagnosis; as such, hormonal status may be implicated in pathogenesis.⁵⁶ Indeed, among the five different subtypes of ovarian cancer, low-grade serous ovarian cancer has the higher proportion of hormone receptor–positive (progesterone receptor– and/or estrogen receptor–positive) tumors.⁵⁷ In this large retrospective study, strong progesterone but not estrogen receptor expression appeared to be associated with improved survival after accounting for site, age, stage, and grade (p = .019 for progesterone and p = .78 for estrogen receptor). But this association was not statistically significant after adjusting for residual disease in this subset of 64 patients with low-grade serous ovarian cancer (p = .27 and .90, respectively).⁵⁷ The agents used as hormonal therapy, which are targeted therapies against the progesterone receptor and estrogen receptor, are mainly tamoxifen and aromatase inhibitors (anastrozole and letrozole). A retrospective study in 64 patients with recurrent low-grade serous ovarian cancer who received 89 separate hormonal regimens showed an ORR of 9% (six CRs and two partial responses).⁵⁸ In total, 61% of the regimens resulted in a progression-free survival (PFS) duration of at least 6 months. Regimens that involved treatment of estrogen receptor–positive/progesterone receptor–positive disease produced a longer median time to progression (8.9 months) than regimens that involved treatment of estrogen receptor–positive/progesterone receptor−negative disease (time to progression, 6.2 months; p = .053). Given the relatively favorable adverse effect profile and demonstrated efficacy, hormonal therapy represents an interesting treatment alternative.

The mitogen-activated protein kinase (MAPK) pathway is activated and appears to play a prominent role in the pathogenesis of low-grade serous ovarian cancer.⁵⁹ Approximately 20% to 40% of low-grade serous carcinomas have a KRAS mutation, whereas BRAF mutations are rare (approximately 5%).^60,61 KRAS is a frequent mutation detected in advanced low-grade serous ovarian cancer, and the BRAF V600E mutation is associated with serous borderline tumors and early-stage low-grade serous ovarian cancer.⁶² As a result, the V600E mutation is associated with a better clinical outcome. In a study of 23 patients with an original diagnosis of serous tumor of low malignant potential who subsequently experienced recurrence with a diagnosis of low-grade serous ovarian cancer, patients with KRAS G12V mutations experienced shorter survival times than those with either KRAS G12D, wild-type, or rare KRAS variants (hazard ratio 4.77; p = .023).⁶³ Another retrospective study showed the potential impact of mutational status; patients with KRAS and BRAF mutations appeared to have better overall survival than those with wild-type KRAS or BRAF.⁶⁴ Additional investigations are warranted to elucidate the role of the mutation type in low-grade serous ovarian cancer, because this may have important clinical implications, such as introduction of the analysis of BRAF/KRAS status in the postdebulking setting to predict the risk of recurrence.⁶⁵

The MAPK cascade is triggered by the binding of a ligand that ultimately leads to phosphorylation of ERK.^66,67 Thus, MEK is a good candidate for targeted therapy, and a number of MEK inhibitors (MEKi) have been developed.

The GOG-0239 open-label phase II study of patients with recurrent low-grade serous ovarian cancer, by prospective pathologic evaluation, received selumetinib (AZD6244)—a MEK1/2 inhibitor that targets the downstream effect of activating BRAF and KRAS mutations—at a dosage of 50 mg twice daily.⁶⁸ The majority of patients had received three or more prior chemotherapy regimens. Fifty-two women with recurrent low-grade serous ovarian cancer were enrolled, and the ORR was 15% (one CR and seven partial responses). Another 65% of patients in the trial had stable disease, and the median PFS was 11.0 months. The most common toxicities were gastrointestinal, dermatologic, and metabolic. Three patients experienced grade 4 toxicities—one each of cardiac, pain, and pulmonary toxicity. Mutational analysis was conducted on formalin-fixed, paraffin-embedded tumor samples from 34 patients enrolled in this trial, and the primary tumor accounted for 82% of the cases. In these 34 cases, there were two BRAF mutations (6%) and 14 KRAS mutations (41%), and 15% of tumors had NRAS mutations. In this study, there was no correlation between mutations of BRAF or KRAS and ORR; however, only hotspot mutations were assessed. Tissue analysis of an extraordinary responder who experienced a complete, durable, and ongoing (> 5 years) response to selumetinib identified a previously uncharacterized MAP2K1 deletion (Q56_V60del). Additional investigations support that this novel deletion is a driver alteration in this exceptional responder and serves as the molecular basis for her dramatic, sustained response to the MEKi.⁶⁹ This finding may explain why targeted genotyping of only the most common hotspot alterations in BRAF and KRAS failed to ascertain the molecular basis for a subset of the responses observed in the GOG-0239 trial and justify the incorporation of broader profiling methods. After these promising results, several studies have been designed, such as the ongoing GOG-281 trial. GOG-281 is a randomized phase II study between investigator choice (of letrozole, tamoxifen, weekly paclitaxel, pegylated liposomal doxorubicin, or weekly topotecan) and the MEKi agent trametinib for recurrent low-grade serous ovarian cancer. The study incorporates prospective pathology review, pretissue biopsy, and blood collection for correlative analyses, such as next-generation sequencing and proteomics. The primary endpoint is PFS, the estimated enrolment is 250 patients, and crossover at disease progression is allowed.

Several additional targeted studies are also ongoing in this space. NCT01936363 was a randomized phase II trial for recurrent low-grade serous ovarian cancer that compared pimasertib (MEKi) plus or minus SAR245409—a phosphatidylinositol-4,5-biphosphate 3-kinase and mTOR. This randomized phase II trial started, and patients were recruited, but the trial subsequently was stopped because of toxicity with the combination. No results have been presented or published as yet. The MILO trial (NCT01849874) is a randomized, open-label phase III study between physician choice (paclitaxel, liposomal doxorubicin, topotecan) and binimetinib, or MEK162, for recurrent low-grade serous ovarian cancer. In addition, the RTM 1313 study is a randomized phase II trial with patients with newly diagnosed stages II to IV low-grade serous ovarian cancer that is investigating trametinib/GSK 214170550 every 3 weeks for six cycles versus standard adjuvant chemotherapy carboplatin/paclitaxel for six cycles. Taken together, biomarkers that predict MEKi activity and the identification of MEKi-independent compensatory pathways are needed.

The angiogenesis pathway may also be a therapeutic target in patients with low-grade serous ovarian cancer. An initial report of three patients with recurrent low-grade serous ovarian cancer treated with bevacizumab, the monoclonal antibody against the vascular endothelial growth factor A (VEGF-A), showed sustained responses of 15-, 15-, and 22-month durations.⁷⁰ From a retrospective cohort of 17 patients with low-grade serous ovarian cancer and serous borderline tumors, two patients were treated with single-agent bevacizumab, and the others were treated with a combination of bevacizumab and chemotherapy.⁷¹ Fifteen patients were evaluable for response; six had a partial response, and five had stable disease that lasted 3 months or longer. The response rate for the low-grade serous ovarian cancer group was 55%. Therefore, additional studies to evaluate the possible role of antiangiogenics in low-grade serous ovarian cancer are warranted, potentially in combination with MAPK inhibitors.

The insulin-like growth factor (IGF) pathway is another pathway overexpressed in low-grade serous ovarian cancer, and related effectors, such as PI3K/Akt/mTOR, have been also described to play a role in disease pathogenesis.⁷² Activating mutations of PI3KCA are observed in approximately 40% of tumors, whereas inactivating PTEN mutations are present in 3% to 8% of tumors.⁷³ AMG-479, a fully human anti–insulin-like growth factor receptor type I monoclonal antibody, had been assessed in frontline and recurrent settings in ovarian cancer but not specifically in low-grade serous ovarian cancer (NCT00718523 and NCT00719212). OSI-906, a tyrosine kinase inhibitor of both IGF-1R and the insulin receptor was assessed in recurrent ovarian cancer (NCT00889382).

On the basis of retrospective studies and ad hoc cooperative group studies, low-grade serous ovarian cancer is described as relatively chemotherapy resistant, which has led to the investigation of novel therapies that are based on the specific molecular pathways of low-grade serous ovarian cancer. Although low-grade serous ovarian cancer is associated with superior overall survival compared with the other histologic subgroups of ovarian cancer, more than 70% of low-grade serous ovarian cancer patients experience relapse and die of their disease. There is an urgent clinical need to develop additional trials of combination targeted agents that are tolerable for the patients and that do not significantly impinge upon quality of life. Because low-grade serous ovarian cancer is a rare entity, the cooperation between different institutes is essential alongside a common effort to reduce heterogeneity of grading and biases in treatment and response evaluation.⁶⁵

Most clear cell ovarian cancer tumors are unilateral at diagnosis, and most are diagnosed at an early stage.⁷⁷ In a prospective randomized trial (JGOG 3017), the proportion of patients with stage I disease was 67%.⁷⁸ The incidence of lymph node metastasis was 9.1% in apparent stage IA tumors, 7.1% in stage IC tumors, and was 10.8% in pT2 tumors.⁷⁷ This stands in contrast with serous ovarian cancers, which were associated with a higher incidence of lymph node metastasis than nonserous tumors.⁷⁹ Although it is controversial, evaluation of lymph node status by surgical staging is recommended, because lymph node involvement in patients with clinical stage I clear cell ovarian cancer was identified as a stronger prognostic factor.⁷⁷

Management of clear cell ovarian cancer with positive peritoneal cytology or surgical rupture remains unclear. Disease progression was observed in 11% of stage IC intraoperative rupture tumors but in only 3% of stage IA tumors.⁷⁷ Progression-free survival of the patients who had stage IC tumors with ascites/malignant washing or ovarian surface involvement was significantly worse than patients who had stage IC disease with capsule rupture during surgery (p = .04),⁷⁷ which implies that positive peritoneal cytology could suggest microscopic implantation of clear cell ovarian cancer cells.

Another important recent observation is the incidence of thromboembolic complication in clear cell ovarian cancer. It has been reported to be higher than in other epithelial ovarian cancers (16.9%–27.3% vs. 0%–6.8%),⁷⁷ and it is also associated with an elevated interleukin 6 level and with worse prognosis.⁸⁰

Several studies that retrospectively analyzed the prognosis of patients in large randomized clinical trials have been reported in terms of difference of prognosis between pathologic subtypes.^81,82 The survival was significantly worse in clear cell than in the serous counterpart in advanced stages, which suggests that clear cell ovarian cancer was resistant to conventional chemotherapy regimens. New cytotoxic regimens, dose-dense paclitaxel regimen,⁸³ and CPT-11 plus cisplatin⁷⁸ did not demonstrate a benefit for clear cell ovarian cancer. Chemotherapy administered intraperitoneally using cisplatin and paclitaxel improved the OS in optimally debulked stage III ovarian cancer, but a survival benefit with intraperitoneal chemotherapy was not observed in clear cell ovarian cancer and mucinous adenocarcinoma.⁸⁴ Therefore, finding new strategies for advanced or relapsed clear cell ovarian cancer is urgent. Finding molecular pathologic characteristics of this disease to direct improvement of targeted therapies is critical.

Investigators from Kyoto University have conducted a series of excellent studies to delineate the pathogenesis of clear cell ovarian cancer from endometriosis (Fig. 3).

FIGURE 3. Hypothetical Carcinogenic Pathway of Clear Cell Ovarian Cancer From Endometriotic Cyst

Abbreviations: IL, interleukin; HNF1β, hepatocyte nuclear factor 1-beta; CCOC, clear cell ovarian cancer.

They first analyzed the content of endometriotic cysts and found that the cysts contained huge amounts of iron, oxidative stress marker LPO, and 8-0HdG, a marker of DNA damage caused by oxidative stress. When the content of an endometriotic cyst or iron was added to immortalized ovarian surface epithelial cells, intracellular reactive oxygen species was elevated, and the contents of endometriotic cyst or iron increased DNA mutations. Therefore, researchers hypothesized that iron-mediated reactive oxygen species may cause DNA mutations and carcinogenesis.⁸⁵

Next, researchers conducted a gene expression microarray analysis and identified clear cell–specific genes, including HNF1B, SOD2, ANXA4 HIF1A, IL6, and STAT3. They enriched gene ontology terms related to oxidative stress and glucose metabolism. Hepatocyte nuclear factor (HNF) 1-beta binds to DNA as either a homodimer or a heterodimer with the related protein HNF 1-alpha. HNF1 alpha and beta share a common biding motif. Genes having the HNF1 binding motif in promoter regions are candidate downstream genes of HNF 1 beta. Interestingly, these genes were upregulated in immortalized ovarian surface epithelial cells by adding the content of endometriotic cysts or iron.⁸⁶ Researchers also conducted a methylation DNA microarray analysis, which revealed that clear cell is distinct from other subtypes in terms of methylation profile. Estrogen receptor pathway genes were hypermethylated and downregulated, whereas HNF1 pathway genes were hypermethylated and upregulated.⁸⁷ Therefore, clear cell ovarian cancer–specific gene expression seems to be stabilized via epigenetic mechanisms.

The researchers also investigated the roles of HNF1B in metabolism of clear cell ovarian cancer cells and found that HNF1B increases glucose uptake by increasing expression of a glucose transporter, GLUT1.⁸⁸ A subsequent metabolome analysis was done and revealed that upregulated HNF1B expression enhances anaerobic glucose metabolism. Known as the Warburg effect, the enhanced anaerobic glucose metabolism has been reported to cause resistance to oxidative stress. Investigators also analyzed the relationship between HNF1B and oxidative stress in clear cell ovarian cancer. Knockdown of HNF1B decreased the amount of glutathione, a redox substance. This was due to decreased intracellular cystine, a substrate for the biosynthesis of glutathione, via the decreased expression of rBAT, a cystine transporter. Then, the investigators found that HNF1B knockdown increased intracellular reactive oxygen species and cytotoxicity by iron-induced oxidative stress. Furthermore, in hypoxia, suppression of HNF1B increased sensitivity to cisplatin. Collectively, HNF1B in clear cell carcinoma causes resistance to oxidative stress and platinum.⁸⁹

Finally, researchers conducted an exome sequencing analysis of clear cell ovarian cancer. ARID1A was the top-mutated gene, and PIK3CA was the second one. Through an integrated analysis of gene mutations and copy number variations, researchers found that the KRAS-PI3K pathway, SWI/SNF complex, and MYC-RB pathway were the most frequently altered pathways (written communication with N. Matsumura, February 2016).

The researchers hypothesize that iron-induced oxidative stress may cause DNA damage and mutations of PIK3CA and ARID1A, which may lead to carcinogenesis of clear cell ovarian cancer. HNF1B plays an important role in the Warburg effect and in resistance to oxidative stress. This may be important for progression in the stressful condition of endometriotic cysts and platinum resistance. Epigenetic changes, gene mutations, and copy number alterations may cause stabilization of clear cell ovarian cancer–specific gene expression and biologic features, including chemotherapy resistance.

Compared with other histologic types of epithelial ovarian cancer, mutation in p53 is less frequent⁹⁰ in clear cell ovarian cancer, and mutation of BRCA1 and BRCA2 is also lower.⁹¹ Wilms tumor suppressor 1 gene (WT1) and the WT1-antisense promoter were significantly methylated in clear cell ovarian cancer (88.2%) compared with serous adenocarcinoma (24%).⁹² PTEN mutation is also frequently observed (27.3%) in this disease.⁹³ Multidrug resistance protein 3 (MRP3)⁹⁴ and HNF1B, which has antiapoptotic effects, are highly expressed.⁹⁵ More recently, frequent alteration of ARID1A⁹⁶ and PIK3CA⁹⁷ has been reported. Mabuchi et al showed that the Akt/mTOR pathway is thought to be the most important passage for tumor growth in clear cell ovarian cancer.^98,99

Recently, Uehara et al¹⁰⁰ conducted genomic analyses on clear cell ovarian cancer and found that, by using microarray analysis, this disease could be classified into three clusters: one that showed fewer alterations of PIK3CA and ARID1A and a better prognosis compared with the two other clusters, which had more alterations.¹⁰⁰ This work suggests that the genomic pattern may be a strong prognostic factor.

As mentioned earlier, the Japanese Gynecologic Oncology Group conducted a randomized phase III trial to compare conventional paclitaxel with carboplatin regimen versus an irinotecan with cisplatin regimen for patients with newly diagnosed stage I to IV clear cell ovarian cancer. This is the first randomized trial specifically on this disease. Unfortunately, there was no survival benefit between the regimens.⁷⁸

On the basis of the molecular profile pattern of clear cell ovarian cancer, the therapeutic target of interest involves the Akt/mTOR pathway. The GOG-268 study tested one of the mTOR inhibitors, temsirolimus, administered in combination with paclitaxel and carboplatin for six cycles and then given for 11 more cycles as a maintenance therapy. Although the results will be presented this year at the 2016 American Society of Clinical Oncology Annual Meeting, we await comparison of results in the United States and South Korea with those obtained in Japan. In addition, the translational component of this trial is underway to evaluate the possible difference on molecular characteristics of advanced clear cell ovarian cancer between Japanese and non-Japanese populations.

Antiangiogenetic agents are also of interest as therapeutic targets for clear cell ovarian cancer. The GOG-254 study evaluated the efficacy and safety of sunitinib and showed that sunitinib was minimally active in the second- and third-line treatments of persistent or recurrent clear cell ovarian cancer. Another antiangiogenetic agent being tested is nintedanib, and a Scottish group is conducting a randomized phase II study to compare nintedanib to other chemotherapeutic agents.

Finally, immunotherapy that uses checkpoint inhibitors is of interest as a treatment strategy. One recent publication on an antibody to PD-1, nivolumab, showed promising signs of efficacy for clear cell ovarian cancer.¹⁰¹

Honoraria: Bayer, Chugai Pharma, Daiichi Sankyo, Eisai, Janssen Oncology, Kyowa Hakko Kirin, Lilly Japan, Nippon Kayaku, Ono Pharmaceutical, Taiho Pharmaceutical, Zeria Pharmaceutical

Consulting or Advisory Role: AstraZeneca, Chugai Pharma, Eisai, MSD, Pfizer, Taiho Pharmaceutical, Takeda

Research Funding: AstraZeneca (Inst), Chugai Pharma (Inst), Eisai (Inst), GlaxoSmithKline (Inst), Immunogen (Inst), Kaken Pharmaceutical (Inst), Lilly (Inst), MSD (Inst), Oncotherapeutics (Inst), Ono Pharmaceutical (Inst), Pfizer (Inst), Shionogi (Inst), Taiho Pharmaceutical (Inst), Zeria Pharmaceutical (Inst)

Speakers' Bureau: Merck

Consulting or Advisory Role: AstraZeneca, AstraZeneca

Research Funding: Dainippon Sumitomo Pharma (Inst)

Honoraria: Intas

Research Funding: AstraZeneca (Inst), Immunovaccine (Inst)

Travel, Accommodations, Expenses: AstraZeneca