Don't blame the weed! Cancer is rarely "caused" by a substance. In fact, a study all through out the 1950's till now, showed that substances are merely the catalist for the growth of cancer. The actual body is to blame. An imbalance in the body itself, which can have an enormous amout of factors, is the primary cause for cancer.
If you take your vitamins, eat healthy and exercise, then you face a substantial chance of never even developing cancer.