Adenocarcinomatous transformation of intracranial germ cell tumors.

Germ cell tumors arising in the gonads, retroperitoneum, and mediastinum are occasionally overgrown by cancers of somatic type that are widely assumed to derive from the "malignant transformation" of included teratomatous tissues. These malignant, nongerminal neoplasms are typically chemoresistant, and their emergence is often associated with fatal treatment failure. Only rare, well-documented reports of sarcomatous transformation complicating intracranial germ cell neoplasia are on record. We describe two nongerminomatous germ cell tumors of the pineal region that underwent transformation into enteric-type adenocarcinoma. Both recurred in a locally aggressive fashion, one proving rapidly fatal owing to the development of multiple cerebral and cerebellar metastases and spinal leptomeningeal adenocarcinomatosis.