N-myc and c-myc amplification was investigated in 27 medulloblastomas. DNA was extracted from 19 formalin fixed and paraffin embedded tumors and from fresh frozen tumor tissue in 8 other cases. The results showed no evidence of amplification of N-myc oncogene and only 1 case had a 27 fold amplification of c-myc. Cytogenetically, this neoplasm presented numerous double minute chromosomes (DMs). Moreover, it had an unusual rapidly aggressive course with massive cerebrospinal fluid dissemination unresponsive to intrathecal chemotherapy. Our results indicate a low incidence of N-myc and c-myc gene amplification in medulloblastomas, suggesting that the oncogenic mechanism in these neoplasms is not closely related to DNA gene amplification. C-myc amplification, although not frequently observed, may however provide a growth advantage for medulloblastoma cells in vivo, favoring their rapid dissemination. Medulloblastomas with c-myc activation may represent a subgroup of tumors with a more aggressive behavior.

A case of choroid plexus neoplasm histologically composed of tubular structures lined by a layer of cuboidal epithelium is reported. The neoplasm was located in the fourth ventricle of a 26-year-old man. The intense positivity for antisera anti-vimentin, anti-cytokeratin, anti-EMA and anti-S100 protein exhibited by these cells was consistent with choroid plexus origin. The patient is alive and in good health 5 years after surgery. The lesion represents a benign choroid plexus neoplasm not previously reported. The name "tubular adenoma of choroid plexus" is suggested for this variant.