Changes in the relative risk and sites of central nervous system metastasis with effective combined chemotherapy and radiation therapy for small cell carcinoma of the lung.

Prolongation of survival of patients with small cell carcinoma of the lung with current effective systemic therapy has been accompanied by a marked increase in the frequency of relapse in the central nervous system (CNS). Prophylactic cranial irradiation (PCI) was shown to reduce the frequency of brain metastasis, but there was no increased short-term survival. Therefore, the necessity for PCI early in the course of treatment has been questioned, especially for patients with extensive disease. From January 1974 through March 1982, 205 patients with small cell carcinoma of the lung were treated at the Medical College of Wisconsin Affiliated Hospitals. None had clinical, radioisotopic, or computed tomographic evidence of brain metastasis. Eighty-two patients received radiotherapy and chemotherapy, but no PCI; 123 patients received combination chemotherapy and radiation therapy with PCI. The cumulative probability of brain metastasis without PCI was 36% at 12 months and 47% at 24 months; the probabilities were 6 and 10%, respectively with PCI. The 24-month probability of brain metastasis in patients with limited disease and no PCI was 45%; for those with extensive disease, it was 47%. No patient presented with extracranial central nervous system (ECNS) metastasis and no one without PCI developed it. Twelve patients who received PCI developed ECNS metastasis; the cumulative probabilities rose to 14% at 12 months and 22% at 24 months. The increased frequency of ECNS involvement has led to a phase I trial of PCI followed by six cycles of combination chemotherapy, without maintenance chemotherapy, followed by irradiation of the chest and spinal cord for patients with complete response.