The National Cancer Institute says it is beginning a nationwide search for people who've defied a diagnosis of terminal cancer and survived, to see if there were genetic changes that allowed them to respond to drug treatments.

Cancer researchers call such people exceptional responders, who have dramatic results from a drug treatment tried more out of desperation than for any medical rationale.

The response of a 58-year-old grandmother from Massachusetts diagnosed with terminal thyroid cancer to a drug normally prescribed only for certain breast, pancreas and kidney cancers has researchers rethinking cancer treatments.

Several months after Grace Silva began treatment with the drug everolimus, the thyroid tumors that had spread into her lungs shrank to nearly nothing, doctors reported in the New England Journal of Medicine.

That is almost unheard of with these types of tumors, called anaplastic thyroid cancer, they said.

"It was a near-complete response," says her oncologist Dr. Jochen Lorch of the Dana-Farber Cancer Institute in Boston. "That in itself is exceptional. When we saw it, it was one of the better days around here."

This type of thyroid cancer is almost always fatal within just months. "No treatment has ever worked," says Lorch.

Researchers who sequenced the genes in tumors that had been removed from Silva found the reason -- a genetic mutation had made her cancer dependent on mTOR, a protein that the drug everolimus suppresses.

Now that such genetic changes have been recognized, investigators can look for the mutations that may make people exceptional responders to the drug, they say.

To that end, the National Cancer Institute has begun a project, the Exceptional Responders Initiative, urging researchers and specialists in cancer across the nation to pass along tumor tissue samples from exceptional responders like Silva so that mutations might be catalogued and any patterns identified.

The identification of unsuspected "response" and "resistance" mutations could help improve treatment of other patients, the researchers said.

"The molecular underpinnings are more important than the tumor type," says Nikhil Wagle of Dana-Farber, first author of journal study. "It's what a lot of us working on precision medicine have been thinking for a long time. The reason people in the field get so excited about this ... is that we want all our patients to be exceptional responders."

The findings of a genetic basis of how a cancer either resists or responds to a drug has implications for more kinds of cancers that just the one Silva had, doctors say.

"The resistance mechanism almost certainly does not just apply to our case," Lorch said.

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