AdenoCA of Colon : Signet Ring Cell
Signet ring cell variant makes up about 1% of all colorectal carcinomas and carries poor prognosis. It affects younger age groups than conventional histologic type. About one-third of cases are associated with MSI (microsatellite instability). Grossly, the most common presentation is diffuse thickening of the bowel wall (linitis plastica). Rare cases may produce a polypoid mass. Microscopically, signet ring cell carcinoma has a diffuse growth pattern and consists of individual cells or small clusters infiltrating the bowel wall. By definition, at least 50% of the tumor volume is composed of signet ring cells. The intracellular mucin blob pushes the nucleus to one side creating the signet ring appearance. The nucleus may be flattened or remain round or oval. Some cases show both intracellular mucin as well as extracellular mucin lakes. Metastases from stomach or breast must be excluded. Immunohistochemical profile is as follows: Positive for: CK20, CDX2, MUC2, MUC5AC; Negative for CK7. Signet ring cell carcinoma of the colon has a tendency to spread along peritoneal surfaces to structures like ovary and omentum. Lymph node involvement is common. The prognosis is extremely poor. This intermediate magnification view shows signet ring cell carcinoma diffusely infiltrating the rectal wall. The lighter areas are composed of signet ring cells in pools of mucin.