The most common and least aggressive form of breast cancer still poses a risk of death more than 10 years after a woman is diagnosed with the disease, according to a new long-term study. The findings could affect how doctors treat women with this type of breast cancer, the researchers said. Their 21-year study of nearly 1,000 women in California found that molecular subtypes of breast cancer were important independent predictors of death from breast cancer. In particular, women with luminal A tumors (a subtype of breast cancer generally believed to have the best prognosis) were still at risk for death from the cancer more than 10 years after their diagnosis.