Surgeons in China have for the first time transplanted a section of liver extracted from a genetically modified pig into a human cancer patient, they reported on Thursday.

The surgeons, who described the procedure in a paper in The Journal of Hepatology, grafted the portion of pig liver onto the left lobe of a 71-year-old patient’s liver after removing the larger right lobe, where a tumor the size of a grapefruit had grown. The lobe with the porcine transplant functioned, producing bile and synthesizing blood clotting factors, the surgeons reported. The patient’s body did not reject the organ graft, which enabled the remaining left lobe of the patient’s own liver to regenerate and grow, the scientists said.

The porcine liver lobe was removed 38 days after the transplant, when complications developed, the surgeons wrote in the report. The patient, who had advanced disease, died a little over five and a half months later. He would not have been eligible to receive a human donor organ in China because he had advanced cancer and hepatitis B-related cirrhosis, the authors wrote.

In a commentary accompanying the study, Dr. Heiner Wedemeyer, a co-editor of the journal, hailed the procedure as a “breakthrough” and a “historical clinical milestone,” although he noted that this was only a single case and that much work remained to be done to prevent complications and excessive blood clotting.

“A new era of transplant hepatology has started,” he wrote.

Dr. Heidi Yeh, an associate professor at Harvard Medical School and a transplant surgeon, said that the researchers had been brave to attempt such a procedure, as preliminary experimental work transplanting livers from gene-edited pigs into nonhuman primates had been unsuccessful, discouraging many scientists.

“I think this is a landmark development,” Dr. Yeh said. “They put a pig’s liver in a human for a month, and the human did fine.”