Former President Jimmy Carter says a recent brain scan showed no signs of cancer while he is being treated with a drug called Keytruda.

Dr. Richard Frank, of the Western Connecticut Health Network, says the drug - which is approved to treat melanoma and kidney and lung cancers - is making revolutionary strides in fighting the disease.

Frank says one-third of his patients, including those with stage 4 melanoma, are seeing impressive results. The treatment involves revving up the body's own ability to fight cancer.

Certain cancer cells have a protein called PD1 that shuts down the immune cells that try to attack a tumor, Frank says. Drugs like Keytura or Pembrolizenmab used in President Carter's treatment for melanoma are called anti-PD1 drugs and involve hourly infusions every two to three weeks.

Frank says that unlike chemotherapy, the anti-PD1 drugs have minimal side effects and do not result in hair loss or nausea.

The drug has not proven effective to treat all forms of cancer, and Frank says that certain patients like those with autoimmune diseases may not benefit from that course of therapy.