Mesothelioma is a rare cancer that’s most commonly found in the lining of the lungs or abdomen, but it can also start in the lining of the heart or testicles in rare cases.

Mesothelioma is most common in men ages 45 to 85. Typically, it occurs in those who’ve been exposed to asbestos, a fibrous mineral used in construction and manufacturing until it was banned by the Environmental Protection Agency in 1989. But not everyone who...