Newfoundland and Labrador's largest health authority has apologized after nine breast cancer patients were given the wrong results — but credits its new quality assurance program for quickly detecting the mistakes. 

Eastern Health said of those nine, eight patients received unnecessary treatment. 

Herceptin was prescribed after they tested positive for an aggressive form of breast cancer. 

The drug helps to treat certain tumours, but it can also cause congestive heart failure. Some patients were taking Herceptin for more than eight months, and in certain cases, some had been receiving chemotherapy.  

Doctors at Eastern Health didn't read the test results properly.

At a new conference on Thursday, CEO Vickie Kaminski told reporters that all patients have been contacted. 

"They've all been talked to today [Thursday] and are relieved that their cancer is not as aggressive as originally thought," Kaminski said.  

Minister of Health and Community Services Susan Sullivan echoed Eastern Health's sentiments on Thursday, crediting the health authority's quality assurance system with spotting the errors early on.

"We have learned from the past, and we have in place now a quality assurance process that I believe is truly making a difference," Sullivan said.

"I think we can assure the people of the province that the quality assurance process that is in place is doing precisely what it should do — it is catching any of these kinds of incidents much earlier in the process."

Sullivan said ensuring the health of the women impacted is top priority, but that moving forward with Eastern Health to figure out the root cause for these errors.

Kaminski said the the quality assurance program is a result of the Cameron Inquiry. 

Justice Margaret Cameron determined that Eastern Health made hundreds of mistakes with hormone receptor tests between 1997 and 2005, and was not aware of those errors because it had almost no quality control measures in place to govern the pathology lab's work.