Medulloblastomas with favorable versus unfavorable histology: how many small blue cell tumor types are there in the brain?

Prognostically favorable and unfavorable variants of medulloblastoma have recently been identified, corresponding to medulloblastoma with extensive nodularity and large cell/anaplastic medulloblastoma, respectively. In an effort to identify clinically relevant grading criteria for medulloblastoma in general, 330 Pediatric Oncology Group (POG) cases were carefully reviewed for presence and extent of histologic anaplasia, nodularity, and desmoplasia. The resulting data was statistically analyzed using event-free and overall patient survival as endpoints. Significant anaplasia (moderate to severe) was identified in 24% of cases and was strongly associated with decreased survival times. Additionally, those with diffuse or extensive anaplasia fared worse than those with only focal anaplasia. Although the study confirmed the favorable prognosis for the rare cases of medulloblastoma with extensive nodularity, lesser degrees of nodularity or desmoplasia were not associated with a statistically significant survival advantage. Medulloblastoma grading based on anaplasia demonstrated a statistically stronger association with patient outcome than clinical staging. Therefore, histologic grading of medulloblastomas seems warranted as a routine diagnostic aid.