What's the No. 1 cause of preventable premature death in the U.S.? What's the No. 1 cancer killer among American men & women? What cancer kills twice as many women as any other cancer? The answer to all of the above is not pancreatic, skin, nor breast cancer. ... It's lung cancer. In 1987, lung cancer surpassed breast cancer to become the leading cause of cancer death in women. Smoking is the leading cause of lung cancers, accounting for nearly 90%of lung cancer deaths.