pathological complete response

A pathological complete response is the lack of all signs of cancer in tissue samples removed during surgery or biopsy after treatment with a drug or with radiation. To establish one, a pathologist examines the samples under a microscope and looks for cancer cells still present after the anticancer treatment. If none can be found, the response is recorded as complete. It is also called pathological complete remission, and is often shortened to pCR.

Knowing whether a cancer is in pathological complete response may help show how well a treatment is working, or whether the cancer will come back, which is why trials that give a drug before surgery report it as a headline figure. It is not the same as a cure. The finding describes only the tissue that was removed and examined, so cancer cells elsewhere in the body would not appear in it, and a clear specimen does not guarantee that the disease will not return. Trials therefore report it alongside survival measures rather than in place of them.