Medulloblastoma and supratentorial primitive neuroectodermal tumors: an institutional experience

To the authors' knowledge there are relatively few data concerning supratentorial primitive neuroectodermal tumors (PNET). The authors retrospectively reviewed all cases of PNET of the brain treated at the study institution to determine whether there was a difference in presentation, overall survival, and recurrence-free survival with regard to tumor location (supratentorium vs. posterior fossa).

Between 1977-1996 33 patients with PNET were diagnosed and treated at 1 radiotherapy center. The median age of the patients was 9 years. The location of the tumor was in the posterior fossa in 25 patients and the supratentorium in 8 patients. The tumor had spread to the neuraxis in six patients; four patients with disseminated neuraxis disease had a supratentorial PNET and two had a posterior fossa PNET. All but three patients received craniospinal irradiation. The primary tumor received > or = 5000 centigray in 27 patients and chemotherapy was employed in 26 patients. The median follow-up was 60 months.

The 5-year overall and recurrence-free survival rates for all patients were 77.2% and 79.6%, respectively. The 5-year overall survival rates were 86.3% for patients with medulloblastoma (posterior fossa PNET) and 46.9% for patients with supratentorial PNET (P = 0.01, log rank test). For overall survival, prognostic factors included radiotherapy dose to the primary site, metastases (M) status, and location of the primary tumor. The 5-year recurrence free survival rates were 89.8% for patients with medulloblastoma and 46.9% for patients with supratentorial PNET (P = 0.003, log rank test). For recurrence free survival, prognostic factors included M status and primary tumor site location; radiation dose to the primary tumor site and patient gender were of borderline significance. In the ten patients with inadequate posterior fossa boost fields judged by Children's Cancer Group criteria, there were two failures, both of which were in the original tumor bed.

Supratentorial PNET has a worse overall survival and recurrence free survival than medulloblastoma. There is a suggestion that radiotherapy boosts in medulloblastoma may not need to encompass the entire posterior fossa because posterior fossa failures primarily are in the tumor bed. Larger studies with longer follow-up are needed to determine whether craniospinal irradiation followed by a boost to the tumor bed is adequate for medulloblastoma patients.