WINDSOR, Ont. - A Windsor, Ont., surgeon who performed two unnecessary mastectomies and has admitted a look into her past will reveal more "cases of concern" has now prompted further investigations.

The probes into what went wrong at Hotel-Dieu Grace Hospital and cases involving Dr. Barbara Heartwell in particular continued to multiply Thursday as both the provincial Ministry of Health and the province's medical regulatory body announced they would look into the situation.

The issue first came to light when Hotel-Dieu Grace Hospital in Windsor found out -- only after inquiries from a reporter -- that Heartwell had removed the breast of a woman who didn't have cancer.

A second woman then came forward after hearing a story so similar to her own.

The hospital started a review of Heartwell's cases, in addition to a separate but overlapping pathology review they have been conducting since November.

The troubling situation requires an external look in addition to the hospital's internal investigations, Ontario Health Minister Deb Matthews said Thursday.

"We think it's important, and they think it's important, that we have people from outside the shop take a look so that we all know what happened, what lessons we have learned and what else we need to do to prevent this from happening in the future," she said.

The ministry will conduct the external review in conjunction with the hospital and the Local Health Integration Network. It's possible the scope of the investigation could be expanded outside Windsor if it is warranted, Matthews said.

The minister stressed the importance of a surgical safety checklist that as of April will be required practice in operating rooms across the province. If the checklist, announced in September, had been in place it could have prevented the most recent mistaken mastectomy case, Matthews has said.

NDP Leader Andrea Horwath said if there was an ombudsman in charge of health, recommendations could have been made after the first incident that could have prevented the second.

"The Windsor situation, I think, reinforces what New Democrats have been calling for for quite some time, and that is ombudsman oversight of the health-care system, both hospitals and long-term care," Horwath said.

The College of Physicians and Surgeons of Ontario also said Thursday it is investigating Heartwell. While spokeswoman Kathryn Clarke said she couldn't provide any more information on the Heartwell investigation, she said in general the college has the authority to conduct broad investigations.

"In those cases we have to have in our possession documentation that establishes reasonable and probable grounds to believe that the doctor may be incompetent or has committed an act of professional misconduct," Clarke said.

Depending on the complexity of the case, investigations can take as little as three months or as long as one year, Clarke said. If evidence of incompetence or misconduct is found, the case goes to a disciplinary hearing, which is open to the public.

Heartwell has indicated the hospital will find additional "cases of concern" in its review involving incorrect pathology reports, officials said.

The hospital also revealed Wednesday it had been doing a pathology review since November and has uncovered seven serious cases of concern, five of which involve Heartwell's patients. In January the hospital suspended the privileges of one pathologist, who was also reported to the College of Physicians and Surgeons of Ontario, officials said.

The pathology issues have so far been confined to that one pathologist, but as they expand the scope of the probe the hospital doesn't know what they may find, he said.

Laurie Johnston of Leamington, Ont., had a mastectomy in November 2009 from Heartwell. The doctor admits she misread the results of a needle biopsy that found Johnston -- a single mother of a teenage daughter -- did not have cancer.

Janice Laporte, whose breast was removed by Heartwell in September 2001 but was told a week after her surgery that she didn't have cancer, came forward publicly after hearing about Johnston.

Laporte sued Heartwell but can't discuss the results because of a confidentiality clause. Johnston has retained a litigation lawyer.