Risk of brain metastasis from small cell carcinoma of the lung related to length of survival and prophylactic irradiation.

The problem of brain metastasis from small cell carcinoma (SCC) of the lung has been appreciated for many years, but the magnitude of the problem has been underestimated. Recent studies have shown that the risk of brain metastasis increase as survival is prolonged. Although prophylactic cranial irradiation (PCI) has reduced the frequency of brain metastases, the effect on risk estimates of differences in the periods of observation was not evaluated. From 1974 through 1979, 131 patients with SCC of the lung who had no evidence of brain metastasis by radionuclide or computerized tomographic scan were treated in the Division of Therapeutic Radiology at the Medical College of Wisconsin Affiliated Hospitals. PCI was started in 1977; 57 patients received it and 74 did not. To correct for the differing periods of observation for the two groups, an actuarial calculation of the probability of brain metastasis was used. The calculated rate of clinical failure in the brain for patients who did not receive PCI was 28% at 12 months and 58% at 24 months. The calculated failure rate of the brain for patients who received PCI was 11% at 12 and 24 months. The difference in the probability of brain metastasis between the patients who did or did not receive PCI is highly significant (P less than 0.01). The true benefit of PCI becomes apparent only when the risk of intracranial metastasis is evaluated by methods that correct for incomplete followup. PCI eliminates the progressive increase in the risk of brain metastasis that accompanies increased survival and is important to maximize the probability for cure of patients with SCC.