An 80-year-old female with pseudomyxoma peritonei due to mucinous cancer of unknown origin — molecular characterization and diagnostic challenges

Primary ovarian mucinous carcinoma is rare representing only 2–3% of primary ovarian carcinomas. Appendiceal mucinous neoplasms are also unique conditions that can be accompanies by pseudomyxoma peritonei. This report presents the case of an 80-year-old female with mucinous carcinoma metastases in the peritoneum, pseudomyxoma peritonei and features that may indicate appendiceal or ovarian origin. Initially, the patient was diagnosed with a left ovarian tumor. During diagnostics, features enforcing ovarian origin included: CK7+, CK20– in peritoneal metastasis, unilateral ovary tumor, moderately elevated CA125, low CEA and no cancer detected in gastroscopy and colonoscopy. Features advocating gastrointestinal tract origin included: CDX2+, mild enlargement of the appendix, high CA19-9, low HE4, CA125/CEA = 24, impression on cecum probably by the enlarged appendix, in PET-CT no metabolic activity in the ovary, metabolic activity in colon/cecum and peritoneal lesions as well as pathologic report suggestion of gastrointestinal origin. The ovaries and appendix were not visualized during laparoscopy. Cytoreductive surgery was not feasible. Genetic profiling of peritoneal metastasis showed alterations in KRAS , GNAS , ARID1A , IDH1 genes. We indicate that genetic profiling of mucinous carcinoma of the appendix and ovary and their metastases is needed to determine new molecular targets for systemic treatment. Moreover, we indicate that surgical assessment of cytoreduction and hyperthermic intraperitoneal chemotherapy (HIPEC) is a key element in the treatment of patients with mucinous tumors in the peritoneum. Finally, we emphasize a need for research into new methods of treating pseudomyxoma peritonei in high-risk patients for whom cytoreduction with HIPEC is not feasible.