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Low-grade Serous Carcinoma

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Low-grade serous carcinoma (LGSC) is a recently recognized entity that makes up about 5% of all ovarian serous carcinomas. It presents about a decade earlier than high-grade serous carcinomas (HGSC). It is often asymptomatic and found incidentally or it may present with abdominal pain, distension and ascites. Most cases are in advanced stage (Stage III) at presentation. Involvement is often bilateral. On imaging, the tumor is usually cystic but may have thick septa or nodular areas with high vascularity.

Grossly, it consists of a multicystic mass with fine papillary projections from its walls. Numerous psammoma bodies may give it a gritty consistency.

Microscopically, it shows many architectural patterns. The invasive component consists of isolated tumor cells and small irregular nests infiltrating desmoplastic stroma. In addition, there are micropapillae or macropapillae surrounded by lacunar spaces. Frequently, there is a component of serous borderline tumor of the usual type or micropapillary variant (seen in this case). The slender, delicate micropapillae show a non-hierarchical branching and arise directly from larger papillary structures. The tumor cells are uniform with mild to moderate nuclear atypia, single prominent nucleolus and low mitotic activity. Numerous psammoma bodies are a frequent finding. Necrosis is absent.

The example of LGSC shown here is from a 45 y/o female who presented with chronic pelvic pain and abdominal distension. The tumor involved both ovaries, uterus, omentum, and large bowel.

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