Asbestos exposure is the primary cause of pleural mesothelioma, a rare and aggressive cancer, but inhaling asbestos also multiplies a smoker’s risk of developing lung cancer fiftyfold or greater.
The carcinogenic risk of asbestos exposure and cigarette smoking is exponentially higher than the risk of each exposure added. This is known as the synergistic effect of asbestos exposure and smoking.
From the asbestos.com link someone else posted: