OSAKA — Two women had their breasts removed by a surgeon at a hospital in Hirakata, Osaka Prefecture, in 1996 and 1998 even though pathological tests showed that their tumors were not cancerous, it was learned Thursday.

The 69-year-old surgeon was chief doctor at Hirakata Municipal Hospital at the time of the incidents and is currently an honorary president of the institution.

Medical records of one of the patients were tampered with to conceal the results of the pathological tests, hospital officials added.

Osaka Prefectural Police have begun questioning the people involved, and hospital staff are talking to the former chief doctor.

One of the patients — in her 70s — was diagnosed as having a cancerous tumor in one of her breasts following an ultrasound test in 1998.

Immediately after surgery began to remove the tumor, the surgeon took a sample and sent it to pathology for testing, the officials said.

The doctor was informed the tumor was benign while still in the operating room, but he continued removing the patient’s breast.

Several days later, a more precise test on the same patient produced the same result. A report was attached to the patient’s medical record, but a sheet of paper was later pasted over it to conceal the test result, the officials said.

The other patient — in her 60s — was diagnosed as having breast cancer in 1996. Similarly, a pathological test conducted while she was in surgery showed that further tests were needed to determine if the tumor was malignant. But the doctor ignored the result and continued to remove her breast.

Kuniaki Yamashiro, chief of the hospital, apologized for the surgeon’s treatment of the patients, calling his actions “inappropriate.”

In a news conference, Yamashiro acknowledged that there were problems in the operation procedure, adding that he will try to learn all the facts about the case as quickly as possible.

The former chief doctor, who was performing operations at the hospital until last month, did not show up at the news conference. He was not identified.