U.S. pathologist David Dabbs says the lessons learned at a St. John's lab can be applied globally. (CBC)

A world-renowned author has told Newfoundland and Labrador's breast cancer inquiry that the mistakes at a St. John's lab will yield lessons for labs everywhere else.

David Dabbs, chief of pathology at Magee-Women's Hospital in Pittsburgh and author of a respected textbook on diagnostic immunohistochemistry, said Tuesday he has no doubt that human error led to hundreds of Newfoundland and Labrador patients receiving inaccurate results.

"I think it is a wake-up call in general, to the global community of everyone who does [hormone receptor] testing in their laboratory and other complex testing for breast cancer patients," Dabbs told reporters after testifying Tuesday at the Cameron inquiry.

Dabbs said the hormone receptor tests used to help determine treatment are complex, and involve dozens of intricate steps. Nonetheless, he said some basics must be followed from the start.

"Whenever tissues are collected from patients, the most important aspect of all is to make sure that those tissues are obtained as quickly as possible and processed in the appropriate fluids," Dabbs said.

Justice Margaret Cameron, who has been collecting evidence as the head of the inquiry since March, has already been told that was not consistent practice within Eastern Health.

Some operating rooms did not have refrigerators, and some tissue samples were left in the open over weekends before they were then processed.

Dabbs said labs elsewhere should learn from what happened with how estrogen receptor and progesterone receptor tests were handled in St. John's.

"It is a critically important test. Patients are going on therapies that are either very expensive and/or have potentially serious side effects," Dabbs told reporters.

"So these tests need to be done correctly."

Meanwhile, Dabbs said that Eastern Health made the right decision when it started retesting samples in 2005, soon after it learned that there were problems with the hormone receptor tests. The tests determine whether a patient can benefit or not from powerful antihormonal therapies, usually Tamoxifen.