The conditional probability of survival of patients with primary malignantbrain tumors - Surveillance, epidemiology, and end results (SEER) data

BACKGROUND, Five-year survival estimates in standard cancer reports provide a general description of disease outcome that is useful for surveillance a nd comparison purposes. However, for cancer survivors these overall surviva l rates may be discouraging, and the relevant question regarding an individ ual is this: Once he or she has survived for a specified period of time, wh at is the probability of survival over the next period of time? METHODS, To address this, conditional survival rates by histology for malig nant brain tumor survivors were estimated using the SEER public use data an d the Portable Survival System, with 19,105 brain and other nervous system patients diagnosed between 1979 and 1993. Given that the survival curve dec lines more rapidly in the first 2 years than in subsequent years, condition al probabilities of surviving 5 years given survival to 2 years and 95% con fidence intervals (CIs) were calculated: As age is a strong prognostic fact or for these tumors, conditional probabilities were also estimated by categ ories of age. RESULTS, Estimated 2- and 5-year relative survival rates for patients with malignant brain and other CNS tumors were 36.2% and 27.6%; however, the con ditional probability of surviving to 5 years, given survival to 2 years, re aches 76.2% (95% CI: 74.8-77.6). Conditional probabilities varied by histol ogy and age at diagnosis. The conditional probability of surviving 5 years after surviving 2 years was 67.8% (95% CI: 62.6-73.1) for patients with ana plastic astrocytomas, 36.4% (95% CI: 31.9-41.6) for patients with glioblast omas, and 74.8% (95% CI:75.3-84.1) for patients with medulloblastomas. CONCLUSIONS. Conditional probabilities provide important and encouraging in formation for those who are brain tumor survivors. The utility of these est imates for other time intervals and other cancers or diseases should be con sidered. (C) 1999 American Cancer Society.