Background: Children younger than 5 years who have posterior fossa (PF) primitive neuroectodermal tumors (PNET) have a poor prognosis. Because the use of low-dose craniospinal radiation therapy (CSRT) alone has been associated with a higher relapse rate in these patients, and because standard dose CSRT is associated with profound late sequelae, the authors embarked on a study using a combination of low-dose CSRT and adjuvant chemotherapy.
Methods: Between January 1988 and March 1990, ten patients with PF PNET were treated on an institutional pilot trial. The trial included 1800 cGy radiation therapy (RT) to the craniospinal axis, a PF boost to 5040-5580 cGy and chemotherapy consisting of vincristine weekly during RT. This was followed by vincristine, cisplatin, and lomustine for eight cycles administered every 6 weeks. Patients between 18 and 60 months of age without evidence of tumor dissemination were eligible for study. Follow-up is available to October 1992, with a median follow-up of 4 years from diagnosis. All patients have completed therapy.
Results: Actuarial survival at just more than 4 years is 69%. Three of the ten patients have died after experiencing relapse. In one, the relapse developed in the spine and brain outside the PF; in the second, concurrently in the PF, brain, and spine; and in the third, only in the spine. In one of the three, one of two initial cerebrospinal fluid cytologic examinations showed one clump of tumor cells, and the other sample appeared normal. Neuropsychologic testing has been a routine aspect of the study. A mean intelligent quotient (IQ) score of 103 in six patients surviving at least 1 year is unchanged from the baseline group score of 107. Five children have been tested at baseline and at 2 years after RT; for these children, baseline IQ was 101 and 2-year IQ was 102. These results stand in sharp contrast to earlier studies from this institution that found children younger than 7 years at diagnosis showing marked IQ losses after RT at 1 and 2-year follow-up.
Conclusions: The results of this study suggest that 1800 cGy CSRT in conjunction with the chemotherapy used may produce less neurocognitive damage, perhaps at the expense of relapse along the craniospinal axis. Better means of improving survival without increasing toxicity are needed.