Invasive micropapillary carcinoma of the colon in ascitic fluid: a case report

Invasive micropapillary carcinoma (IMPC) is defined as having characteristic pathologic features of small papillary cell clusters surrounded by lacunar spaces and is known as an aggressive variant in advanced stages due to the high incidence of lymph node metastasis. IMPC has been well described in other organs, including the breast, urinary bladder and lung but has been rarely described in the large intestine. To our knowledge, this is the first report of the cytology of colorectal lesion of IMPC in the English-language literature.

A 64-year-old woman presented with abdominal pain, nausea and constipation. Ascitic fluid cytology showed adenocarcinoma with papillary features, and a colectomy specimen showed IMPC. The cytologic features of this case were characterized by small papillary clusters with a smooth surface showing peripherally located cytoplasm with a rare central lumen, as "inside-out" cell clusters; these findings suggested IMPC. Differentiation from adenocarcinoma of other organs may be difficult, but immunohistochemical profiles suggested a colorectal origin; it was positive for CK20 and negative for CK7.

IMPC has a distinctive cytomorphologic appearance, and this entity can be suggested from ascitic fluid cytology.