Micropapillary variant of embryonal carcinoma: clinicopathological correlation and histochemical study.

Micropapillary pattern of growth (MPG) of carcinoma is a unique morphologic pattern. It is uncommon but a predictor of poor outcome. MPG has not been described in any germ cell tumor, most notably embryonal carcinoma, which may have papillary configuration. In this study, we reviewed 25 primary testicular germ cell tumors (pure or mixed) containing embryonal carcinoma and 2 lymph node metastases with embryonal carcinoma. Five of the 25 primary cases demonstrated MPG. With available clinical information, 3/3 (100%) cases with MPG and 5/12 (42%) cases without MPG showed evidence of metastases. The 2 lymph node metastases contained predominantly MPG. At metastasis, the median tumor size in primary tumors with MPG was significantly smaller than in those without MPG. Reticulum staining was negative in the regions of MPG and positive for other coexisting non-micropapillary growth patterns in all the 6 embryonal carcinomas. In conclusion, we described MPG in embryonal carcinoma. Although limited by the number of cases, our clinicopathological correlation results raised the possible association of the presence of MPG to the high-rate metastasis of embryonal carcinoma, similar to that seen in other carcinomas with MPG. It is therefore of importance to document this variant growth pattern if present in embryonal carcinoma. We also demonstrated that reticulum is a useful negative marker for identification of MPG.