Carcinomas with micropapillary morphology: clinical significance and current concepts.

Invasive micropapillary carcinoma has been recently recognized as a rare but distinctive variant of carcinoma in various anatomic sites, including breast, urinary bladder, lung, and major salivary glands. Morphologically, it is characterized by small tight clusters of neoplastic cells floating in clear spaces resembling lymphatic channels. Most often this growth pattern is mixed with a variable component of conventional carcinoma or other variants. In addition to a unique morphology, tumors with invasive micropapillary growth share a high propensity for lymphovascular invasion and lymph node metastases. Patients have typically high-stage disease at presentation and a poor clinical outcome compared with that of patients with conventional carcinoma arising in the same organ site. In this article the author reviews the available literature on tumors displaying a micropapillary component.