Not many studies have been done on Comfrey for Cancer but the allantoin and rosmarinic acid in comfrey has been studied for cell regrowth and is showing that it can be effective for regeneration of healthy cells that will help with stopping the growth of abnormal cancer cells. The very compounds that help with bone remodeling can help with cell regrowth. According to Sloan Kettering more research needs to be done on its application to cancer.  The NIH have studied for many other applications and have found that it is very effective topically and research done on treatment that is common in the Moldivia with comfrey for hepatitis is also worth more investigation as it showed better results than a prescribed medicine.

It has not been recommended for any specific cancer and should be used sparingly Internally it could be used as a tea especially for healing in the stomach, lungs and esophagus.  A slave, ointment or decoction could be used to soothe skin irritations from cancer treatments.