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Low-grade serous carcinoma of the ovary is an uncommon lesion, composing approximately 3% of ovarian neoplasms. It typically arises in association with a serous borderline tumor and is most often at an advanced stage upon diagnosis. Gene mutations in BRAF and KRAS are characteristic. Various histologic architectural patterns are known, such as papillary, micropapillary, inverted micropapillary, glandular and nested. We report a case of low-grade serous carcinoma arising years after a serous borderline tumor and contralateral teratoma; the low-grade serous carcinoma showed two patterns: micropapillary growth and a previously unreported form of solid pattern manifesting as large tumor islands without slit-like spaces. This unusual solid morphology raises the differential diagnosis of high-grade serous carcinoma, which would result in different clinical management. The presence of areas with classic micropapillary architecture, in addition to the absence of high-grade cytonuclear atypia and marked pleomorphism, support the diagnosis of low-grade serous carcinoma. Immunohistochemical stains for p53 and p16 failed to show abnormal patterns characteristic of high-grade serous carcinoma. The patient declined chemotherapy and is on letrozole; she has had recurrent right pleural effusions over six months of follow-up after surgery. [ABSTRACT FROM AUTHOR]