Hôtel-Dieu Grace Hospital officials speak with reporters about the error. From left, spokeswoman Kim Spirou, CEO Warren Chant and former chief of staff Dr. Art Kidd, who resigned in December. (CBC)

A hospital in Windsor, Ont., has launched a full investigation into how a surgeon removed a woman's breast after misreading a report that said the woman did not have cancer.

'It was a serious error. It is heartbreaking.'— Warren Chant, hospital CEO

Dr. Barbara Heartwell, a surgeon with 28 years of experience, performed the mastectomy on Laurie Johnston of Leamington, Ont.

Another doctor had given the initial diagnosis of cancer, but a pre-surgery pathology report found that Johnston did not, in fact, have cancer.

Heartwell misread that final report, and proceeded with the single mastectomy on Nov. 5.

CBC News met with Johnston at her home in Leamington late Thursday, hours after Hôtel-Dieu Grace Hospital made the error public.

She would not speak on tape, but told CBC she has felt very alone throughout her ordeal, which began in late 2009.

Johnston told CBC News she wants the hospital to be held responsible for what happened to her, so that it doesn't happen to anyone else.

She said she does not want to ever see Heartwell again, but has not launched a lawsuit against the hospital.

Media call triggers investigation

The hospital said Heartwell only discovered her mistake when doing a post-surgery report.

"Let me say that we are extremely saddened by this event," said Warren Chant, the hospital's CEO. "It was a serious error. It is heartbreaking."

Heartwell broke the news to Johnston in a followup visit, but failed to immediately inform her supervisors of the mistake, said hospital officials.

The hospital's disclosure policy requires physicians to notify all appropriate hospital personnel, said Dr. Art Kidd, who was chief of staff at the time of the surgery, but has since resigned.

Instead, hospital officials learned about the mistaken mastectomy in a phone call from a local media outlet on Feb. 5 three months after Johnston's breast was removed.

In the two weeks that followed, the hospital said it contacted Johnston to offer her counselling and other assistance.

"We are profoundly sorry that this has occurred," said Chant.

Hospital to double-check surgeon's work

The hospital said Heartwell is currently on a scheduled vacation to care for a sick relative, but that the experienced surgeon is "remorseful and devastated" by what they said was the first medical mistake in her 28-year career.

Heartwell has continued to see patients since Johnston's November surgery, but the hospital said the doctor will be monitored and her pathology reports independently analysed.

The hospital is also reviewing her entire mastectomy case history.