A new wave of experimental cancer drugs that directly recruit the immune system's powerful T cells are proving to be immensely effective weapons against tumors, potentially transforming the $100 billion global market for drugs that fight the disease.

But top oncology researchers are concerned about the two emerging technologies, citing dangers seen repeatedly in clinical trials including the potentially fatal buildup of toxic debris from killed tumor cells and damage to healthy tissue. Such side effects could block regulatory approval if they aren't controlled, researchers and drug company executives said.

In some trials, the two new approaches, known as CAR T cells and bispecific antibodies, have eliminated all traces of blood cancers in 40 percent to 90 percent of patients who had no remaining options. The drugs could reap annual sales in the tens of billions of dollars for their manufacturers, especially if they can also eliminate solid tumors in such terminally ill patients.