Ontario's medical college says a pathologist investigated in a probe sparked by two unnecessary mastectomies will not be licensed to practise medicine in the province as of Wednesday.

The College of Physicians and Surgeons of Ontario began looking into Dr. Barbara Heartwell  and pathologist Dr. Olive Williams  after it was revealed two women found out after mastectomies that they didn't actually have cancer.

Williams was suspended and later resigned from Hotel-Dieu Grace Hospital in Windsor, Ont., and has not practised pathology since then.

The college's inquiries, complaints and reports committee has now decided that if Williams wants to return to pathology she must advise the college, complete an educational program and be under supervision for a year.

Williams has also decided not to renew her medical licence, which expires Tuesday.

The college decided not to discipline Heartwell.

A provincial investigation into Hotel-Dieu Grace Hospital and the work of Williams and Heartwell uncovered "significant concerns" with the work of the pathologist.

The probe reviewed more than 6,000 reports back to 2003, and investigators had moderate or major disagreements with the original diagnosis in 221 of the cases by Williams.

Forty-five of those cases warranted further investigation, treatment or patient follow-up, and eight patients were notified because they needed a change in treatment or additional investigation and follow-up.

However, the report concluded that Williams was within an acceptable discrepancy rate of 10 per cent.

Dr. Barry McLellan, who led the probe, said he couldn't say whether cataracts contributed to potential errors by Williams, as alleged in an internal document by health officials.

Janice Laporte, whose breast was removed by Heartwell in September 2001, was told a week after her surgery that she didn't have cancer.

In November 2009, Laurie Johnston of Leamington, Ont., had a mastectomy performed by Heartwell, who admitted she misread the results of a needle biopsy that found Johnston did not have cancer.

Johnston is suing both Williams and Heartwell. Both doctors have filed statements of defence.