SOX6 Expression Is Sensitive for Peritoneal Epithelioid Malignant Mesothelioma, But Not Specific in the Differential Diagnosis With Tubo-ovarian Serous Neoplasia.

Primary peritoneal malignant mesothelioma (MM) can demonstrate morphologic overlap with low-grade and high-grade tubo-ovarian serous neoplasms; it is also biologically and prognostically distinct from benign mesothelial proliferations. Currently, there is no single biomarker that can definitively distinguish these neoplasms. Sex-determining region Y box 6 (SOX6) immunohistochemistry has been recently described to differentiate pleural epithelioid MM from lung adenocarcinoma, but it has not been evaluated in the peritoneum. SOX6 immunohistochemistry was performed on 43 peritoneal epithelioid MM, 7 peritoneal biphasic MM, 5 well-differentiated papillary mesotheliomas, 5 serous borderline tumors, 29 low-grade serous carcinomas (LGSCs), 20 high-grade serous carcinomas (HGSCs), and 25 cases of peritoneal reactive mesothelial hyperplasia. Quantitative SOX6 expression in epithelioid MM (median, 100% of tumor cells) was significantly greater than in LGSC/serous borderline tumor (median, 90%; P=0.004) and HGSC (median, 45%; P=0.0001). However, when SOX6 is expression is defined as ≥10% of tumor cells, there was no significant difference in the rate of SOX6 positivity between epithelioid MM (41/43, 95%), LGSC (28/29, 97%; P=1.0), and HGSC (17/20, 85%; P=0.16). Quantitative extent of SOX6 expression in epithelioid MM was significantly greater than in biphasic MM (median, 0%; P=0.0001), well-differentiated papillary mesothelioma (median, 20%; P=0.001), and reactive mesothelial hyperplasia (median, 20%; P=0.0001), but not significantly different from flat quiescent mesothelium (median, 90%; P=0.82). SOX6 immunohistochemistry is 95% sensitive for peritoneal epithelioid MM, but is also consistently expressed in LGSC and HGSC, negating its usefulness in this common differential diagnosis. SOX6 also shows variable expression across the spectrum of reactive, benign neoplastic, and malignant mesothelial lesions of the peritoneum, and does not appear to be diagnostically useful in distinguishing benign from malignant mesothelial proliferations.

Extrauterine Mesonephric-like Neoplasms: Expanding the Morphologic Spectrum.

Mesonephric-like adenocarcinomas (MLA) are rare neoplasms arising in the uterine corpus and ovary which have been added to the recent 2020 World Health Organization Classification of Female Genital Tumors. They have similar morphology and immunophenotype and exhibit molecular aberrations similar to cervical mesonephric adenocarcinomas. It is debated as to whether they are of mesonephric or Mullerian origin. We describe the clinical, pathologic, immunohistochemical, and molecular features of 5 cases of extrauterine mesonephric-like proliferations (4 ovary, 1 extraovarian), all with novel and hitherto unreported features. These include an origin of MLA in extraovarian endometriosis, an association of ovarian MLA with high-grade serous carcinoma, mixed germ cell tumor and mature teratoma, and a borderline ovarian endometrioid tumor exhibiting mesonephric differentiation. Four of the cases exhibited a KRAS variant and 3 also a PIK3CA variant. In reporting these cases, we expand on the published tumor types associated with MLA and report for the first time a borderline tumor exhibiting mesonephric differentiation. We show the value of molecular testing in helping to confirm a mesonephric-like lesion and in determining the relationship between the different neoplastic components. We provide further evidence for a Mullerian origin, rather than a true mesonephric origin, in some of these cases. We also speculate that in the 2 cases associated with germ cell neoplasms, the MLA arose out of the germ cell tumor.

Ki67 does not predict recurrence for low-grade appendiceal mucinous neoplasms with peritoneal dissemination after cytoreductive surgery and HIPEC.

Low-grade appendiceal mucinous neoplasms (LAMN) can disseminate to become low-grade mucinous carcinoma peritonei (LGMCP), which is optimally treated with cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS/HIPEC). Approximately half of the patients with LGMCP recur despite complete cytoreduction, and risk factors for recurrence are poorly understood. We sought to evaluate if Ki67 predicts progression of LGMCP after CRS/HIPEC. A retrospective review of a prospectively maintained database was performed to identify patients treated with complete CRS/HIPEC for LGMCP from 2008 to 2019 with Ki67 assessed. Patient characteristics, histologic data, average and focally high "hotspot") Ki67 index, progression-free survival (PFS), and overall survival (OS) were analyzed. Ki-67 immunostain was performed on the histologic section with the highest cellularity and architectural complexity. Forty-four patients with LGMCP (55% male, median age 61) were identified. The median Ki67 score and hotspot Ki67 score was 15% (1-70) and 50% (1-90), respectively. On univariate analysis, average Ki67 and hotspot Ki67 were not predictive of PFS when analyzed as continuous normalized values (HR 1.0, p = 0.79 and HR 1.1, p = 0.38, respectively) or as categorical values when stratified by the median (HR 0.9, p = 0.67 and HR 1.0, p = 0.93). This remained true on multivariate analysis when stratified for peritoneal cancer index, CEA, and completeness of cytoreduction score for both normalized Ki67 and hotspot Ki67 (HR 0.9 [95% CI 0.8-1.3], p = 0.94 and HR 1.04 [95% CI 0.8-1.3], p = 0.73, respectively). Ki67 failed to predict disease recurrence for patients with LGMCP in this cohort.

Talc and mesothelioma: mineral fiber analysis of 65 cases with clinicopathological correlation.

Malignant mesothelioma is strongly associated with prior asbestos exposure. Recently there has been interest in the role of talc exposure in the pathogenesis of mesothelioma. We have analyzed lung tissue samples from a large series of malignant mesothelioma patients. Asbestos bodies were counted by light microscopy and mineral fiber concentrations for fibers 5 µm or greater in length were determined by scanning electron microscopy equipped with an energy dispersive spectrometer. The values were compared with 20 previously published controls. Among 609 patients with mesothelioma, talc fibers were detected in 375 (62%) and exceeded our control values in 65 (11%). Elevated talc levels were found in 48/524 men (9.2%) and 17/85 women (20%). Parietal pleural plaques were identified in 30/51 informative cases (59%) and asbestosis in 5/62 informative cases (8%). Commercial amphiboles (amosite and/or crocidolite) were elevated in 52/65 (80%) and noncommercial amphiboles (tremolite, actinolite or anthophyllite) in 41/65 (63%). Both were elevated in 34/65 (52%). Asbestos body counts by light microscopy were elevated in 53/64 informative cases (83%). A history of working in industries associated with asbestos exposure and increased mesothelioma risk was identified in 36/48 cases in men, and a history of exposure as household contacts of an occupationally exposed individual was identified in 12/17 cases in women. We conclude that among patients with mesothelioma, the vast majority have talc levels indistinguishable from background. Of the remaining 11% with elevated talc levels, the vast majority (80%) have elevated levels of commercial amphibole fibers.

Pathological prognostic factors of pseudomyxoma peritonei: comprehensive clinicopathological analysis of 155 cases.

BACKGROUND: Pseudomyxoma peritonei (PMP) is an extremely rare malignancy, characterized by extensive peritoneal implantation and colloidal ascites. This study was to explore the pathological prognostic factors of PMP. METHODS: Specimens from 155 PMP patients were analyzed by H&E and immunohistochemistry. Parameters included primary tumor location, histological grade, lymph node metastasis, tumor emboli in the blood and lymph vessels, perineural invasion, Ki67 labeling index, p53, mismatch repair (MMR) gene mutations, MUC1, MUC2, MUC5AC, and MUC6. Clinicopathological and follow-up data were subjected to univariate and multivariate analyses. RESULTS: The patients included 63.2% (n = 98) low-grade mucinous carcinoma peritonei, 31.6% (n = 49) high-grade mucinous carcinoma peritonei and 5.2% (n = 8) high-grade mucinous carcinoma peritonei with signet ring cells. There were 9.7% (n = 15) with lymph node metastasis; 11.6% (n = 18) with angiolymphatic invasion; 6.3% (n = 8) with defective MMR (dMMR); 35.5% (n = 55) with Ki67 labeling index ≥ 50%; 36.1% (n = 56) with p53 mutation. For PMP from appendiceal origin (n = 140), univariate analysis identified 10 potential prognostic factors. But Multivariate analysis identified only histologic grade was the independent prognostic factor for OS. Mortality risk of high-grade peritoneal mucinous carcinoma or high-grade peritoneal mucinous carcinoma with signet ring cells was 7.056 times (P < .0001, 95% CI: 2.701-18.435) or 27.224 times (P < .0001, 95% CI: 6.207-119.408), respectively, higher than low-grade. CONCLUSIONS: For PMP from the appendiceal origin, histological grade could be the only independent prognostic factor.

Uterine pleomorphic leiomyosarcoma with osteoclastic giant cells: Case report with peritoneal washing cytology and cell block study.

Uterine leiomyosarcoma (LMS) with osteoclastic giant cells (OGCs) is extremely rare. However, its morphological appearance and aggressive behavior may have resulted in its being diagnosed as so-called giant cell malignant fibrous histiocytoma (MFH) in the past. Effusions are not uncommon in LMS and may be indicative of an unfavorable prognosis. We report a case with the cytological appearance of a uterine LMS with OGCs metastatic to lower pelvic peritoneum. The pelvic washing specimen consisted of three-dimensional aggregates of atypical cells. The cytohistologic and immunohistochemical study obtained from the cell block and the tumor mass showed overlapping features such as bizarre pleomorphic spindle cells containing numerous evenly dispersed OGCs. The malignant tumor cells showed extensive positivity for desmin, h-caldesmon and multifocal positivity for smooth muscle actin (SMA) whereas OGCs stained with CD68. We stress the usefulness of performing cell block and subsequent immunohistochemistry in order to make an accurate cytohistologic correlation.

A set of molecular markers predicts chemosensitivity to Mitomycin-C following cytoreductive surgery and hyperthermic intraperitoneal chemotherapy for colorectal peritoneal metastasis.

Cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) is associated with significant perioperative morbidity and mortality. We aim to generate and validate a biomarker set predicting sensitivity to Mitomycin-C to refine selection of patients with colorectal peritoneal metastasis (CPM) for this treatment. A signature predicting Mitomycin-C sensitivity was generated using data from Genomics of Drug Sensitivity in Cancer and The Cancer Genome Atlas. Validation was performed on CPM patients who underwent CRS-HIPEC (n = 62) using immunohistochemistry (IHC). We determined predictive significance of our set using overall survival as a surrogate endpoint via a logistic regression model. Three potential biomarkers were identified and optimized for IHC. Patients exhibiting lower expression of PAXIP1 and SSBP2 had poorer survival than those with higher expression (p = 0.045 and 0.140, respectively). No difference was observed in patients with differing DTYMK expression (p = 0.715). Combining PAXIP1 and SSBP2 in a set, patients with two dysregulated protein markers had significantly poorer survival than one or no dysregulated marker (p = 0.016). This set independently predicted survival in a Cox regression model (HR 5.097; 95% CI 1.731-15.007; p = 0.003). We generated and validated an IHC prognostic set which could potentially identify patients who are likely to benefit from HIPEC using Mitomycin-C.

ΔNp73 status in peritoneal and ovarian dissemination of appendicular adenocarcinoids (goblet cells).

INTRODUCTION: Goblet cell carcinoma (GCC) is an appendicular neoplasia representing less than 5% of all appendicular tumors, found in 0.3-0.9% of the appendectomies, 35-58% of all appendicular neoplasms, and less than 14% of malign appendix tumors. The most frequent clinical presentation is abdominal pain associated with a picture of acute appendicitis. MATERIALS AND METHODS: We present 3 clinical cases of appendix GCC, 2 subjected to cytoreductory surgery plus intraperitoneal hyperthermic chemotherapy and a third, who is currently receiving neoadjuvant treatment with a good response to chemotherapy and who will be offered the same treatment as the first two patients. Given the unpredictable behavior of these tumors, the use of molecular markers could help us to predict their behavior and prognosis. In this context, the TP73 gene would make an interesting putative marker. ∆Np73 has been described as overexpressed in a great variety of tumor types including colon cancer and this up-regulation is associated with a poor prognosis. To evidence its role in this malignancy, we evaluate here the status of ∆Np73 in the primary tumor and normal counterpart tissues, in the metastatic implants and in healthy areas of the peritoneum from the appendicular GCC patients. In addition, we checked the expression levels of this p73 variant in the tumor and normal tissue of 26 patients with colon cancer. RESULTS: Remarkably, 2 patients showed significant ∆Np73 down-regulation in both the primary tumor and the implants. Case 1 presented a fourfold decrease of levels in the primary tumor and 20-fold decrease in the implants. Case 2 showed a seven- and fourfold down-regulation in the primary tumor and implants, respectively. However, Case 3 showed an up-regulation of 53- and threefold in the primary tumor and implants, respectively. CONCLUSION: Goblet cell carcinoma of the appendix is very rate. It tends to seed throughout the peritoneum, making aggressive surgical cytoreduction and chemotherapy viable treatment options. Investigation into the molecular basis of these tumors may improve the diagnosis, prognosis and therapeutic decisions regarding these patients. ∆Np73 seems a good candidate for further analysis in longer series.

IMP3 as a prognostic biomarker in patients with malignant peritoneal mesothelioma.

Malignant peritoneal mesothelioma (MPeM) is an incurable cancer with poor prognosis, and several biomarkers have been suggested for screening of MPeM. The aim of our study was to evaluate the prognostic significances of IMP3 and Fli-1 in MPeM. Diagnostic biopsies of 44 MPeM patients were centrally collected and were immunohistochemically analyzed for expression of IMP3, Fli-1, and Ki-67. Labeling was assessed by 2 pathologists. Complete clinical information and follow-up were obtained from patients' records. Carcinomas expressed Fli-1 in 42 (95.5%) of 44 specimens, and IMP3 in 23 (52.3%) of 44 specimens. Spearman ρ analysis revealed that Fli-1 expression was related to both histologic type and Ki-67 labeling index (Ki-67LI; r = -0.500, P < .05; r = 0.358, P < .05), and IMP3 expression was related to Ki-67LI (r = 0.401, P < .05). A Kaplan-Meier analysis and univariate Cox regression analysis showed that tumor-directed treatment, a lower peritoneal carcinomatosis index, stage I, lower Ki-67LI, and lower level of IMP3 expression had a statistically significantly positive effect on overall survival; Fli-1 did not affect overall survival in the univariate analysis (hazard ratio [HR], 1.026; P = .904). A Kaplan-Meier analysis showed the correlation between IMP3-Fli-1 and overall survival, whereas univariate and multivariate Cox regression analyses did not confirm the correlation. Cox regression analysis revealed that IMP3 expression (HR, 2.311 [95% confidence interval, 1.190-4.486]; P = .013) and no tumor-directed treatment (HR, 0.189 [95% confidence interval, 0.086-0.416]; P = .000) retained independent prognostic significance, both with negative effect on OS. IMP3, along with tumor-directed treatment protocols, is a powerful prognosticator in patients with MPeM.

Comparative clinicopathological and cytomorphological analyses of peritoneal carcinomatosis associated with metastatic breast carcinoma and primary peritoneal/ovarian carcinoma in patients with a history of breast carcinoma.

Causes of peritoneal carcinomatosis (PC) in patients with a history of breast carcinoma include both metastatic breast carcinoma (MBC) and primary peritoneal/ovarian carcinoma (PPOC). The origin of PC is important to determine the appropriate treatment strategy. Cytological examination of the peritoneal fluid (PF), which may be the first diagnostic approach to PC, is of distinct value in confirming the presence of malignant cells and determining the origin of PC. We analyzed the clinicopathological and cytomorphological characteristics of 33 patients with a history of breast carcinoma whose PF cytology contained malignant cells. Cases showing positive immunoreactivity for PAX8 and a lack of GATA3 expression were considered as PPOC. Sixteen patients developed PC caused by PPOC. PPOC patients were characterized by early-stage primary breast carcinoma, absence of non-peritoneal MBC before PC, and normal serum levels of CEA and CA15-3. Fourteen PPOC patients had pathogenic germline BRCA mutations. Cytological examination revealed that most of the PPOC cases had a dominant papillary arrangement of the tumor cells with severe nuclear pleomorphism, occasional bizarre nuclei, and atypical mitotic figures. Patients with PPOC who underwent cytoreductive surgery had a significantly longer survival time compared to those who did not, or MBC patients. In patients with a history of breast carcinoma presenting with PC, the presence of early-stage primary breast carcinoma, no prior non-peritoneal MBC, and a dominant papillary cellular arrangement pattern in the PF cytology were independent predictors of PPOC. Cytoreductive surgery significantly improved survival for patients with PPOC.

Malignant peritoneal mesothelioma in patients with endometriosis.

AIMS: Florid mesothelial hyperplasia is known to result from endometriosis. Well-differentiated papillary mesothelioma and multiloculated peritoneal inclusion cysts have also been described in women with endometriosis. To our knowledge, peritoneal diffuse malignant mesothelioma (MM) arising in the setting of endometriosis has not been reported. The purpose of this study is to report the clinicopathological characteristics of women with MM and endometriosis. METHODS: The surgical pathology files of a tertiary academic medical centre and the consultation files of one of the study authors were reviewed for cases of MM in females with and without endometriosis. RESULTS: Six women with MM and endometriosis ranging in age from 29 to 55 years (median=45 years) were identified. All had peritoneal MM and endometriosis involving the peritoneum and/or adnexa. Five had epithelioid MM and one had biphasic MM. Two had paraoccupational exposure to asbestos. The median age of women with MM and endometriosis (44.5 years) was significantly less than the median age of cases without endometriosis (58.0 years) (p value=0.01). CONCLUSIONS: To our knowledge, this is the first report of MM in women with endometriosis. Interestingly, MM in the setting of endometriosis has only been observed in the peritoneum and not in other serosal cavities. The findings in the present study suggest that chronic serosal inflammation secondary to endometriosis may be an inducing factor in rare cases of MM of the peritoneum.

Successful treatment of a giant ossified benign mesenteric schwannoma.

Primary benign schwannoma of the mesentery is extremely rare. To date, only 9 cases have been reported in the English literature, while mesenteric schwannoma with ossified degeneration has not been reported thus far. In the present study, we present the first giant ossified benign mesenteric schwannoma in a 58-year-old female. Ultrasound, computed tomography and magnetic resonance imaging were used, but it was still difficult to determine the definitive location and diagnose the mass. By laparotomy, a 10.0 cm × 9.0 cm × 9.0 cm giant mass was found in the mesentery and was then completely resected. Microscopically, the tumour located in the mesentery mainly consisted of spindle-shaped cells with a palisading arrangement. Some areas of the tumour were ossified, and a true metaplastic bone formation was observed, with the presence of bone lamellae and osteoblasts. Immunohistochemical investigation of the tumour located in the mesentery showed that the staining for the S-100 protein was strongly positive, while the stainings of SMA, CD34, CD117 and DOG-1 were negative. The cell proliferation index, measured with Ki67 staining, was less than 3%. Finally, a giant ossified benign mesenteric schwannoma was diagnosed. After surgery, the patient was followed up for a period of 43 mo, during which she remained well, with no evidence of tumour recurrence.

PAX8 Expression in a Subset of Malignant Peritoneal Mesotheliomas and Benign Mesothelium has Diagnostic Implications in the Differential Diagnosis of Ovarian Serous Carcinoma.

Distinguishing malignant peritoneal mesothelioma (MPM) from serous carcinoma involving the peritoneum remains a diagnostic challenge, particularly in small biopsy and cytology specimens. In this distinction, PAX8 expression has been regarded as a specific marker of serous carcinoma. In addition, BAP1 loss is reportedly specific to MPM, in the distinction from both benign mesothelial lesions and ovarian serous tumors (OSTs). Using immunohistochemistry, we examined PAX8 and BAP1 expression in 27 MPMs, 25 cases of benign mesothelium, and 45 OSTs. Five MPMs were PAX8 (5/27, 18%), while 8 cases of benign mesothelium expressed PAX8 (8/25, 32%). PAX8 expression in mesothelium was significantly more common in women than in men (P=0.01). Sixteen MPMs exhibited BAP1 loss (16/25, 64%), while BAP1 was retained in all benign mesothelium and all OSTs. All cases of PAX8 mesothelium were negative for expression of estrogen receptor. These data show that PAX8 is expressed in both benign and malignant mesothelium, and that BAP1 loss is highly specific for MPM, in the differential with both benign mesothelial proliferations and OTSs. These results also have implications for primary diagnosis and for pathologic staging of OST. Caution should be applied when PAX8 expression is used to distinguish mesothelial and serous proliferations, and BAP1 loss may be confirmatory in cases where mesothelioma is favored.

[Clinical and pathologic features of extrapleural sarcomatoid mesothelioma].

Objective: To investigate the morphological features, diagnosis and differential diagnosis of extrapleural sarcomatoid malignant mesothelioma (SMM). Methods: Six cases of extrapleural SMM were evaluated for their clinical, histological, immunohistochemical features, and prognosis. Results: Patients included 3 men and 3 women, with a median age of 60 years (range 41-75 years). All patients had no asbestos exposure in history and no pleural lesions. The tumors involved peritoneum (3 cases), bone (2 cases), and neck soft tissue (1 case). Histologically, the tumors were mainly composed of slender to plump spindle cells with occasional polymorphic cells, arranged in fascicular to storiform pattern or haphazardly organized, closely resembling those of fibromatosis, fibrosarcoma or malignant fibrous histiocytoma. The tumor cells were imunohistochemically positive for cytokeratin (pan, 6/6), calretinin (5/6), podoplanin (6/6), D2-40 (4/6), vimentin (6/6), WT1 (4/6), CD10 (3/6), SMA (4/6), and variably positive for CK7, and CK8/18, but were negative for other linage-specific markers. The Ki-67 proliferation indexes ranged from 25% to 55%, consistent with the diagnosis of malignant mesothelioma of the sarcomatous type. Ultrastructurally, the tumor cells possessed discontinuous external lamina, cytoplasmic processes, microfilaments and desmosomal intercellular junctions. Local recurrence or metastasis was seen in 1 case and 4 cases, respectively, after surgery, and all the patients died of the disease within 9 months. Conclusions: Extrapleural SMM, although rare, should be considered as a differential diagnosis among other benign or malignant sarcomatoid tumors and sarcomas. Along with clinical and radiological presentation, the combination of broad-spectrum cytokeratin, vimentin, and a series of mesothelial markers are useful for diagnosis of SMM.

Reproducibility for histologic parameters in peritoneal mesothelioma.

Histologic subtype is recognized as a prognostic factor in malignant pleural mesothelioma. Specifically, epithelial morphology is associated with a better prognosis than other subtypes, and the same association is observed in peritoneal malignant mesothelioma. Recently, prognostic differences based on morphologic subtypes of epithelial peritoneal malignant mesothelioma were reported. Herein, we report the interobserver variability across four pathologists at three institutions. The authors independently reviewed 67 cases of malignant peritoneal epithelioid mesotheliomas and subclassified them according to their epithelial subtype: papillary, tubulopapillary, trabecular, micropapillary, solid and/or pleomorphic. The cases were also evaluated by each author for several other histopathologic parameters including depth of invasion, nuclear grade, lymphocytic host response, mitotic count/index, presence of lymphovascular invasion, and stromal desmoplasia. The interobserver agreement for histopathologic parameters was highest for mitotic rate (κ=0.36) and primary epithelial subtype (κ=0.32). The interobserver variability for solid subtype pattern was moderate (κ=0.49). We found that the interobserver variability for most histopathologic parameters is poor.

A randomised, open-label, phase 2 study of the IDO1 inhibitor epacadostat (INCB024360) versus tamoxifen as therapy for biochemically recurrent (CA-125 relapse)-only epithelial ovarian cancer, primary peritoneal carcinoma, or fallopian tube cancer.

OBJECTIVE: Indoleamine 2,3-dioxygenase-1 (IDO1) is a key regulator of immune tolerance in ovarian cancer. This study investigated efficacy and safety of the IDO1 enzyme inhibitor epacadostat versus tamoxifen in patients with biochemical-only recurrence (CA-125 elevation) following complete remission after first-line chemotherapy for advanced epithelial ovarian, primary peritoneal, or fallopian tube cancer. METHODS: In this open-label, phase 2 study (NCT01685255), patients were randomised 1:1 to epacadostat 600mg or tamoxifen 20mg twice daily for successive 28-day cycles and stratified by time since completion of first-line chemotherapy to first CA-125 elevation (3 to <12 or ≥12months). The primary endpoint was investigator-assessed progression-free survival (PFS; RECIST v1.1). Secondary endpoints included CA-125 response (Gynecologic Cancer InterGroup criteria), overall survival, safety, and tolerability. RESULTS: The study was terminated primarily due to slow accrual and lack of evidence of superiority. Median PFS was 3.75months for epacadostat (n=22) versus 5.56months for tamoxifen (n=20; HR, 1.34 [95% CI, 0.58-3.14]; P=0.54). Of evaluable patients, 1 (5.0%) epacadostat and 3 (15.8%) tamoxifen patients had confirmed CA-125 responses. The most common treatment-emergent adverse event was fatigue (epacadostat, 36.4%; tamoxifen, 40.0%). Immune-related adverse events, observed with epacadostat only, were primarily rash (18.2%) and pruritus (9.1%). Epacadostat pharmacokinetics/pharmacodynamics were consistent with its known mechanism of action. IDO1 expression was observed in 94% of archival tumour samples. CONCLUSIONS: This first report of immunotherapy evaluation in biochemical-only relapse ovarian cancer and of IDO1 inhibitor monotherapy in ovarian cancer found no significant difference in efficacy between epacadostat and tamoxifen. Epacadostat was generally well tolerated.