All smoke contains polycyclic aromatic hydrocarbons and exposure to them over long periods of time may be linked to cancer. You are extremely unlikely to develop lung cancers from smoking marijuana because it is not radioactive like tobacco smoke.
Tobacco is grown with phosphate fertilizers mined from the mineral apatite. Apatite also contains radium, polonium 210 and lead 210. These radioactive elements accumulate on growing tobacco leafs and ultimately end up in the lungs of the people who smoke it. Research has shown polonium 210 to be the only component of tobacco smoke that will cause lung cancer on its own when inhaled by mice.
THC and other cannabinoids have also shown themselves to be powerful antioxidants capable of halting the growth of tumors.