Alberta health officials have ordered a review of an additional 1,600 reports from an Edmonton pathologist after 29 patients were mistakenly told they didn't have prostate cancer or had a less aggressive form of the disease.

The 29 cases were among 159 prostate biopsy slides, taken between July and September, that were reviewed by a pathologist working at the Royal Alexandra Hospital in Edmonton.

Fifteen men were told they didn't have cancer when they actually did. In 14 other cases, the pathologist underestimated how aggressive the cancer was.

"I'd like to sincerely apologize for any distress and concern that this incident will have or has caused patients and families in Alberta," said Dr. Chris Eagle, president and CEO of Alberta Health Services.

Alberta Health Services has so far retested 126 of the 159 prostate biopsies. The tests came under scrutiny last month after a urologist raised concerns over what he saw while operating on a patient.

"The urologist at the time of surgery noticed that there was a difference between the severity of the cancer he was noting and what was recorded on the specimen that had come from the previous prostate biopsy," Eagle said.

Alberta Health Services will review an additional 1,568 non-prostate specimens interpreted by the same pathologist between July and September.

Alberta Health Minister Fred Horne addresses an Edmonton news conference about the Royal Alexandra Hospital pathology review as Alberta Health Services CEO Dr. Chris Eagle looks on. Briar Stewart/CBC News

"Those specimens will be prioritized to ensure that the most urgent cases, such as lung biopsies, are re-read first," Alberta Health Minister Fred Horne said.

Retesting of the first set of 159 questionable biopsies will continue through the weekend and are expected to be completed next week. Eagle said patients could be fast-tracked through the system if it's found that their treatment needs to change.

So far, retests on 51 of the prostate biopsies have led to the same results. There were minor differences in another 46 biopsies that could prompt a small change in treatment, Eagle said.

The now-retired physician is no longer working for Alberta Health Services. The problems weren't discovered until after he left his position. The College of Physicians and Surgeons has been alerted.

Alberta Health Services is not releasing his name.

"He's a senior physician," Eagle said. "A person who has had a career in Alberta and is competent."

Anyone who has had a biopsy at the Royal Alexandra Hospital in the last six months can call the Alberta Health Services hotline at 1-866-301-2668.