Hôtel-Dieu Grace Hospital in Windsor, Ont., is investigating a second case in which Dr. Barbara Heartwell performed a mastectomy in 2001 on a patient who did not have cancer.
Hospital officials made the admission late Tuesday night. Heartwell is a surgeon with 28 years' experience.
"Today the hospital received detailed information about another event in which a patient was harmed," said Kim Spirou, the hospital's vice-president of communications and development.
The mistake was uncovered after the hospital began a review of Heartwell's patient files last week following revelations of another error involving a patient under her care.
In that case, Heartwell performed a single mastectomy in the fall of 2009 on a woman who was initially told she had breast cancer.
It was only after the surgery that Heartwell told the patient she had made a mistake, and that the woman did not have cancer.
The error was brought to the attention of the hospital when the victim approached a local reporter with her story.
At the time, the hospital said Heartwell had misread a pre-surgery pathology report that ruled a lump in the woman's breast was benign.
"The hospital is deeply troubled by these incidents and is firmly resolved to fully investigate and take whatever measures are required," its CEO Warren Chant, said in a statement Tuesday.
"In the best interests of our patients, Dr. Heartwell has volunteered to temporarily withdraw from performing surgery pending the outcome of the hospital's investigation."