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

Abstract

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.

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