Simultaneous p53 and KRAS mutation in a high-grade serous carcinoma with deceptive appearance of a low-grade carcinoma. A case report.

Low-grade and high-grade serous carcinomas have unique clinical, morphological, underlying molecular alterations, and vastly different biologic behavior (Prat et al., 2018, Vang et al., 2009). The differentiation into high and low-grade serous carcinoma is important for clinical management and prognosis and is easily recognized by practicing pathologists. High-grade serous carcinoma is characterized by marked nuclear atypia and pleomorphism, frequent, often atypical mitosis with papillary or three-dimensional clusters, p53 mutation, and block-like p16 staining. In contrast, low-grade serous carcinomas have a different morphologic appearance with micropapillary formation, small nests of tumor cells having low to intermediate grade nuclei, and absence of significant mitosis. Low-grade serous carcinoma is often associated with micropapillary variant of ovarian serous borderline tumor. The low-grade serous carcinoma shows wild type p53 expression, patchy p16 staining, and often K-RAS, N-RAS, and/or B-RAF mutation. Here we report a case of mullerian high grade serous with a deceptive morphology resembling low-grade serous carcinoma with micropapillary features and moderate nuclear atypia. However, the tumor is simultaneously p53 and K-RAS mutated. This case illustrates three critical issues; a) potential to be mistaken as a low-grade serous carcinoma because of morphologic appearance and relative uniform cytologic feature. b). raise the question of true progression of low-grade to high-grade serous carcinoma, a rare phenomenon as described in the literature, and c). whether the biologic behavior and/or response to therapy would differ from the classic forms.