An elephant's tusks are not molars but massively overgrown upper incisors — front teeth. The Chinese characters for ivory use the character for "molar," adding to the misconception, but anatomically tusks grow from the front of the jaw.
If more cells mean higher cancer risk, whales and elephants should constantly get cancer. Yet they rarely do—less often than smaller animals. This contradictory phenomenon is called "Peto's paradox."