Primitive neuroectodermal tumours of the cerebrum. Pathology and treatment.

Eighteen cases of cerebral tumour composed partly or totally of primitive embryonal cells are reported. These lesions comprise 2.8% of all primary cerebral hemisphere tumours in the histopathology files of The Royal Marsden Hospital between 1971 and 1980 inclusive. Most exhibited some degree of differentiation towards neuronal or glial elements and, as more than one type of differentiation was often present in the same lesion, we agree with others that the term primitive neuroectodermal tumour (PNET) is more appropriate to describe these lesions than terms based on histogenesis. The extent of the primitive component varied, but usually accounted for more than 80% of the tumour. Although the tumours bear some similarities to posterior fossa medulloblastomas, they exhibit important differences in histology, immunohistology, natural history and response to treatment. Nearly all PNETs examined expressed some glial fibrillary acidic (GFAP) both in primitive areas and zones of astrocytic differentiation. GFAP staining may thus be of value in distinguishing PNETs from undifferentiated non-neurogenic tumours. Of 14 patients referred for radiotherapy, the survival rate at 3 years was 29% (4/14) and 5 years 25% (3/12). Patients with tumours in which at least 90% of the tissue was undifferentiated exhibited an extremely poor prognosis with none of 9 patients still alive at 3 years in contrast to 3 of 5 patients (60%) with tumours showing less than 90% undifferentiation. Radical tumour removal, where feasible, followed by irradiation of the whole cerebrospinal axis is recommended. Adjuvant chemotherapy with such agents as CCNU and Vincristine may be of value: the 3 long term survivors in the present series (7-11 years), including one who presented disseminated intracranial disease, received such adjuvant treatment.