Concurrent High-Grade Serous Carcinoma with Mucinous Differentiation and Ectopic Complete Molar Pregnancy of the Fallopian Tube: A Case Report.

Objective: We report the first documented case of concurrent ectopic complete hydatidiform mole (CHM) and high-grade serous carcinoma (HGSC) of the fallopian tube, associated with unique histologic features and mutations in the HGSC.

Case report: The patient presented with pelvic pain and vaginal bleeding. Laboratory examination revealed a positive urine pregnancy test and high serum beta-human chorionic gonadotropin (β-hCG). Transvaginal ultrasound demonstrated a left adnexal mass suspicious for ectopic pregnancy. Salpingectomy was performed, and the fallopian tube, noted to be ruptured with a visible ectopic pregnancy, demonstrated chorionic villi with diffuse hydropic enlargement and mild trophoblast hyperplasia. p57/Kip2 immunohistochemical staining (IHC) showed loss of expression in villous cytotrophoblasts and stromal cells, confirming CHM. An incidental 0.5 cm focus of HGSC was identified in the fallopian tube, associated with serous tubal intraepithelial carcinoma (STIC). The tumor exhibited solid, transitional cell carcinoma-like, and acinar patterns, with intraluminal mucin highlighted by Alcian blue and PAS-D stains. Patient underwent staging surgery which resulted in the finding of a 0.7 cm HGSC in the left ovary with morphology concordant to the tubal mass, except for a pseudo-endometrioid pattern in the ovary. Notably, the HGSC is positive (2+, 90%) for FOLR1 antigen and harbored a pathogenic mutation (p.R273H) in exon 8 of the TP53 gene.

Conclusion: This report emphasizes the crucial role of meticulous sampling and histopathologic examination of the fallopian tube, including the fimbriae, in all salpingectomy specimens. Furthermore, the case highlights the broad spectrum of morphologies encountered in HGSC, including mucinous differentiation. HGSC should be in the differential diagnosis when encountering mucin-producing high-grade carcinoma.