In a long-term study of older men diagnosed with low-risk prostate cancer and followed with active surveillance, less than a third of cases eventually needed treatment, according to a new study. About one half of one percent of the men died of their cancer during up to 18 years of follow-up. Some prostate cancers do need to be treated on diagnosis, but older men with small, slow-growing cancers may die of other causes — often heart disease — before their prostate cancer shortens their lifespan, the authors note August 31 in the Journal of Clinical Oncology.