Hundreds of women in Quebec with breast cancer may have been prescribed the wrong treatment because of faulty pathology tests, a CBC News investigation has found.

In Newfoundland and Labrador, the issue surfaced recently, as Eastern Health's pathology lab turned over inaccurate hormone receptor tests to almost 400 patients over an eight-year period. More than 100 women died.

Worried that the same problem could occur in Quebec, the province's pathology association took 15 breast cancer tissue samples, had them tested by a reliable lab and then sent the samples to labs across the province asking them to retest for hormone receptors.

Radio-Canada investigative TV program Enquête obtained the results of the association's investigation:

• 15 to 20 per cent of the hormone receptor tests got the wrong result.
• 30 per cent of tests looking for the HER2 protein were wrong. (The test is used to determine which chemotherapy treatment is best.)

"If we think that there's about 10 to 30 per cent variation, then it's a significant number of people out there with a wrong diagnosis," said Dr. Louis Gaboury, president of Quebec's Association of Pathologists.

Hundreds of women could be affected, Gaboury said.

Lower-quality pathology testing has severe consequences on patients who might not be offered the right treatment, said Gaétan Barrette, president of Quebec Federation of Medical Specialists.

Chronic underfunding in the province led to a drastic lack of pathologists, training and poor equipment, Barrette said, adding Quebec is one step away from what happened in N.L.

"The conditions over there were not optimal," Barette said. "They're exactly the same in this province, and we could go through the same issue in this province, and that would be very sad."

Some oncologists and pathologists in Quebec said tests done at laboratories showing the worst results should be done over, regardless of how costly or time-consuming it may be.