[Difficult interpretation of combined serous neoplasia of the peritoneum and fallopian tube: clinical and morphological observation].

The lack of established criteria for the assessment, classification, and staging of rare tumors of the female reproductive organs represents a significant challenge in gynecologic oncology. We propose potential approaches to the assessment of such neoplasms using the example of combined serous neoplasia of the peritoneum and fallopian tube. In an 84-year-old female patient with verified endometrioid adenocarcinoma of the corpus uteri, histological examination of the surgical specimen revealed combined neoplasia of the greater omentum and fallopian tube. Immunohistochemical examination revealed positive expression of ER, p16 (heterogeneous reaction), and p53 ("wild-type"), and negative expression of WT1 and MLH1/PMS2. The omental and fallopian tube tumors demonstrated a WT1+/PAX8+/Ber-EP4+ immunophenotype with preserved expression of MMR proteins. Mutations in the NRAS, KRAS, or BRAF genes were not detected. Following a comprehensive analysis, a diagnosis of primary multiple malignancies was established: endometrioid adenocarcinoma of the uterine corpus G1 (MMR-deficient molecular subtype) and low-grade serous adenocarcinoma of the peritoneum with involvement of the greater omentum (invasive implants) and fallopian tube (non-invasive implants). This case highlights the need to analyze similar cases to refine international classifications and clinical guidelines.