STRN-ALK rearranged malignant peritoneal mesothelioma-Presenting with bilateral extensive pelvic masses in a young woman: Mimicking low-grade serous ovarian carcinoma.

Malignant peritoneal mesothelioma (MPM) is an exceptionally rare tumor type. Although some somatic/germline genetic alterations including BAP1 loss have been identified in some cases, the molecular properties of MPMs are remained poorly understood. In recent years, anaplastic lymphoma kinase (ALK) gene rearrangement was revealed in a subset of (3.4%) MPMs. Low-grade serous carcinomas (LGSCs) are a rare subtype of ovarian carcinoma and have some morphologic and immunophenotypic overlapping features with MPMs and this may cause misdiagnosis in daily practice. Here, we report a case of 18-year-old women with STRN-ALK-rearranged MPM and no previous exposure to asbestos. This case was presented with bilateral pelvic masses and histologically was displaying pure papillary morphology with mild-to-moderate nuclear atypia, psammoma bodies, and diffuse PAX8 expression as LGSCs. With the detection of ALK alteration in some of the MPMs, a targeted treatment option has emerged for these unusual tumor types.