Comprehensive analysis of PD-L1 expression, HER2 amplification, ALK/EML4 fusion, and mismatch repair deficiency as putative predictive and prognostic factors in ovarian carcinoma.

Most ovarian carcinomas (OC) are characterized by poor prognosis, particularly the most frequent type high-grade serous carcinoma. Besides PARP inhibitors, target-based therapeutic strategies are not well established. We asked the question which other therapeutic targets could be of potential value and, therefore, analyzed a large cohort of OC for several predictive factors. Two hundred eighty-eight (288) cases of OC including the major histological types were analyzed by immunohistochemistry for PD-L1HER2, ALK, and the mismatch repair (MMR) proteins MLH1, PMS2, MSH2, and MSH6. HER2 amplification and ALK/EML4 fusion were assessed by fluorescence in situ hybridization. The most frequent finding was PD-L1 expression ≥ 1% in 19.5% of the cases, which correlated with a significantly better overall survival in multivariate analysis (p < 0.001). HER2 amplification was detected in 11 cases (4%), all high-grade serous carcinomas. Amplification of HER2 did not correlate with patients' survival. ALK/EML4 fusion was found in two cases (0.74%): one high-grade serous and one endometrioid carcinoma. MMR deficiency was only present in one case of stage IV high-grade serous carcinoma. Subsets of high-grade serous carcinomas show PD-L1 expression and HER2 amplification, respectively, and, therefore, could qualify for immune checkpoint inhibitor therapy or anti HER2 therapy. PD-L1 is also of prognostic impact. ALK/EML4 fusion is very rare in OC and not a putative therapeutic target.