Newfoundland and Labrador's largest health authority is apologizing to nine breast cancer patients after discovering the women were improperly treated.
Eastern Health says the nine women were told they had aggressive tumours. But results of a quality assurance program in December showed that the women had less aggressive tumours.
Eight of the women were over-treated with the drug Herceptin.
On Thursday, Eastern Health met with all nine patients to inform them of the change in their test result and to advise them of the need for a treatment change.
"On behalf of Eastern Health, I want to publicly apologize to those nine patients," Eastern Health resident and CEO Vickie Kaminski said in a statement.
"This is a very distressing time for our patients and their families and we are offering whatever support they need at this time."
Herceptin, when used with chemotherapy, can cut the risk that breast cancer will recur in women whose cancer over-express HER-2, a protein that causes cancer cells to divide and grow aggressively.
But the drug can also cause side effects for the heart, liver and lungs and is thus recommended only in those cancer patients in whom it will help.
Kaminski told The Canadian Press that so far, oncologists have told her that the patients who were overtreated with Herceptin haven't suffered side effects, but she says doctors will need to continue to monitor them.
The problem with the HER2 testing was discovered Dec. 9, when Eastern Health workers noticed a lab test result did not match with one during a quality assurance test. The health board stopped its testing and sent new tests to an external lab.
It then began to review all HER2 testing cases between April 23 and Dec. 9, 2013, which led to discovery of the nine faulty test results.
In 2009, Eastern Health was the subject of a large judicial inquiry into testing errors in its pathology lab, which affected hundreds of breast cancer patients.
The authority established a quality assurance program as a result.
Kaminski said the one bright spot about the incident demonstrates that Eastern Health's Quality Assurance program is working by catching the errors quickly.
"The quality assurance program allows us to detect any discordant results early; that we put a process in place to determine whether there is an issue; and, most importantly, that we can adjust treatments for our patients if required," she said.