The Toronto pathologist who redid nearly 1,000 breast cancer tests from the troubled labs of Eastern Health in 2005 told the Cameron inquiry in St. John's Thursday that he had quickly noticed a troubling trend in the samples he received.

"I was very concerned about the quality of the material that I was looking at," said Dr. Brendan Mullen, a pathologist with Mount Sinai Hospital in Toronto.

Mount Sinai handled the retesting of hormone receptor tests from Eastern Health in 2005.

Mullen testified that he saw problems with how the tissue samples were prepared and preserved.

He told the inquiry he wouldn't have put up with the problem if the samples had been coming from his lab.

"I might tolerate the first one," Mullen said, but a second or third mistake would not be acceptable. "Excuse the expression, all hell would break loose," he said.

"I could pick out issues because I was seeing them repeatedly, not only day after day, but within the same day, so you're much more attuned to what the issues are," Mullen said.

Testing requires complex procedure

The inquiry heard there are dozens of steps to preparing a sample for testing, beginning when a piece of human tissue is taken from someone through a biopsy. The specimen must be properly refrigerated and preserved before a rigorous preparation to stain it with chemicals so certain characteristics are highlighted.

The stained sample is preserved in a block of wax that's sliced into very minute portions, which are then sealed on a glass slide so they can be viewed under a microscope. The inquiry heard the process involves using exact amounts of chemicals and performing certain steps within a specific time.

Mullen told the inquiry he'd had concerns that if quality control was a problem at the Eastern Health lab, it would affect not only the hormone receptor tests, but also other specimens in the lab.

Mullen said he wrote to the lab's clinical chief, Donald Cook, in early 2006, saying he would like to talk about the technical problems he had encountered.

No one ever responded, Mullen said.