The Odd Couple: An Extremely Rare Coexistence of Ovarian Serous Carcinoma and Low-grade Appendiceal Mucinous Neoplasm.

Serous neoplasms are the most frequently encountered tumors of the ovary, typically arising as primary lesions. In contrast, mucinous tumors of the appendix are well-documented for their association with mucinous ovarian tumors and pseudomyxoma peritonei. To date, only one case has been reported in the literature describing the synchronous occurrence of a serous ovarian neoplasm and an appendiceal mucinous tumor. We present the second documented case of a low-grade appendiceal mucinous neoplasm (LAMN) occurring concurrently with a serous carcinoma of the ovary. A 68-year-old postmenopausal female presented with abnormal vaginal bleeding and was found to have a pelvic mass on imaging, raising suspicion for an ovarian malignancy. She underwent radical hysterectomy with a prophylactic appendectomy. Histopathological analysis confirmed a diagnosis of low-grade serous carcinoma in the left ovary, with an incidental finding of LAMN noted in the appendix. This rare coexistence highlights the importance of recognizing such rare association, as the distinction between serous and mucinous ovarian tumors is clinically significant due to their differing biological behaviors and treatment strategies. This case also provides detailed histopathological and immunohistochemical insights supporting the distinct diagnoses of these two neoplasms.