It was a small trial, just 18 rectal cancer patients, every one of whom took the same drug. But the results were astonishing. The cancer vanished in every single patient, undetectable by physical exam, endoscopy, PET scans or M.R.I. scans. Dr. Luis A. Diaz Jr. of Memorial Sloan Kettering Cancer Center, an author of a paper published Sunday in the New England Journal of Medicine describing the results ... said he knew of no other study in which a treatment completely obliterated a cancer in every patient. "I believe this is the first time this has happened in the history of cancer," Dr. Diaz said. Dr. Alan P. Venook, a colorectal cancer specialist at the University of California, San Francisco, who was not involved with the study, said he also thought this was a first. A complete remission in every single patient is "unheard-of," he said. These rectal cancer patients had faced grueling treatments " chemotherapy, radiation and, most likely, life-altering surgery that could result in bowel, urinary and sexual dysfunction. Some would need colostomy bags. They entered the study thinking that, when it was over, they would have to undergo those procedures because no one really expected their tumors to disappear. But they got a surprise: No further treatment was necessary. "There were a lot of happy tears," said Dr. Andrea Cercek, an oncologist at Memorial Sloan Kettering Cancer Center and a co-author of the paper. Another surprise, Dr. Venook added, was that none of the patients had clinically significant complications.