Invasive micropapillary carcinoma of the sigmoid colon: distinct morphology and aggressive behavior.

We report a case of invasive micropapillary carcinoma of the sigmoid colon in a 72-year-old female with anemia and abdominal pain. Grossly, the tumor demonstrated a deeply invasive, ulcerated fungating mass. Microscopically, the carcinoma was predominantly composed of micropapillae with reversed cell polarity, abundant neutrophils, and surrounded by clear spaces. Multifocal lymphovascular invasion was present with extensive lymph node metastasis. Immunohistochemically, the carcinoma cells were positive for CDX2, CK20 and monoclonal carcinoembryonic antigen. They were negative for CK7. The stroma-facing surface of the micropapillae was positive for CD10 and villin, confirming the inside-out growth pattern characteristic of micropapillary carcinoma. Work-up for distance metastasis was negative. The patient was alive and well 1.5 years after sigmoidectomy and postoperative chemotherapy.