The effect of age on treatment choice and survival in elderly breast cancer patients. To investigate the effect of age on treatment choice and survival in patients with breast cancer, data from the cancer registry of the Netherlands Cancer Institute (NKI, Amsterdam, The Netherlands) on 611 women have been analyzed. All patients 55 years and older admitted to the NKI for primary treatment of breast cancer between 1981 and 1986 were selected. For women 75 years and older, physicians were less likely to use treatment of adjuvant radiation therapy after a mastectomy and more often employed primary hormonal therapy only for local stage disease than for younger patients. Life-table analysis showed that disease-specific survival at 7 years for patients 65 through 74 years of age was significantly better (65%) than that of the youngest (55%) and the oldest age group (50%). In multivariate regression analysis (Cox), age older than 74 years was significantly and independently associated with a shorter disease-specific survival as compared with patients younger than 75 years. This difference in survival, however, does not seem to be the result of the difference in treatment between the age groups, but suggests an influence of age-related factors such as comorbid diseases and weak physical condition, which manifest themselves most strongly in the oldest age category and make the older woman more vulnerable to the course of malignant disease. 