Beer said he should have done more tests on the Auckland woman's tissue sample, but the pressure to assess the biopsy specimen and five others within 90 minutes was a major factor.
That was because BreastScreen Aotearoa - the Ministry of Health unit responsible for breast cancer screening - set a five-day deadline for breast cancer diagnosis.
"It was one of those cases where I was rushed," Beer said. "When you are interpreting pathology, you shouldn't be rushed."
Beer, the New Zealand Society of Pathologists' president and former Waikato Hospital clinical director for anatomic pathology, said laboratory staff were being "set up to fail". He and other members of the society want the deadline doubled to 10 days, matching the turnaround expected for other types of biopsy.
Engels' case, where her tissue samples were placed in the wrong processing cassette, was a classic example of rushed staff making mistakes, Beer said.
Neither Engels nor the Dunedin woman were BreastScreen Aotearoa patients, but urgent processing of breast biopsy specimens had become standard practice everywhere, Beer said.
Most breast biopsies were processed in batches because of the time constraints, when it would be better to process them in between those of other biopsies. "That way those testing them are not looking at similar biopsies one after the other," Beer said.
Multi-disciplinary meetings held between health experts to agree on a diagnosis were also too rushed.
"We might have 40 cases to deal with in 90 minutes. That's two minutes of discussion [each]."
In an emailed response to Beer's concerns, BreastScreen Aotearoa clinical adviser Dr Marli Gregory said the five-day deadline reduced the anxiety women faced while waiting for results. And Beer acknowledged those waiting for results would be stressed and want an answer as soon as possible. "But do you want a quick result or do you want the right result? If it was my wife, I wouldn't be happy with a five-day turnaround."
Engels, buoyed last week by community support after telling her story, agreed.
"The most important thing is to get a correct diagnosis."
Beer dreaded hearing about more women coming forward to say they had been misdiagnosed.
"I'm just wondering, 'My God, is there another one out there?' I wouldn't be surprised."
THREE WEEKS OF REVELATIONS
May 20, 2012: Health officials order an urgent investigation after a woman had her breast removed when she was misdiagnosed as having cancer. The woman's test results were switched with another patient who has since been given the heartbreaking news that she has breast cancer. The Herald on Sunday reports the women, both from Otago, had biopsies after their mammograms indicated they had suspicious lesions.
May 27, 2012: Jenny Engels, who had her left breast removed after being wrongly told she had cancer, calls for an urgent review of diagnostic laboratories. Four weeks after the disfiguring surgery she was told about the error.
June 3, 2012: Leading Waikato pathologist Ian Beer reveals he has misdiagnosed a woman, in a third case to be revealed by the Herald on Sunday. She had a breast removed after being wrongly advised she had cancer. Dr Beer calls for longer time for biopsy reports, saying the five-day turnaround is too rushed.
SYSTEM WORKS, SAYS MINISTER AS INQUIRY ORDERED
The Government has ordered an internal inquiry after the Herald on Sunday revealed the botched biopsies of five women.
But Associate Health Minister Jo Goodhew insists women can still have faith in the breast cancer screening system.
She has asked chief medical officer Dr Don Mackie to look for similarities between the cases, once the three district health boards have completed their investigations.
But her response has been slammed as inadequate by Labour's health spokeswoman Maryan Street, who said medical staff were under pressure to meet deadlines so the Government could show it was "churning out results".
Three women have lost breasts after being wrongly diagnosed with cancer, while two others with the disease were given the all-clear.
Senior Waikato pathologist Dr Ian Beer reveals in today's paper that he was responsible for one misdiagnosis, and said more mistakes would happen unless laboratory staff were given more time to make breast cancer diagnoses.
"I take my hat off to him for going public," Street said.
"If they are being made to do things in a way that might compromise the quality of their work then none of us is well served."
Goodhew, whose office is responsible for the breast screening programme, said she was devastated by the women's ordeal.
"My heart just sank when I heard about it. I certainly hope there are not others."
She understood the public would be worried by the spate of mistakes - "I'm concerned too" - but she believed women could have faith in the service.
She said each BreastScreening Aotearoa office was regularly audited.
She had asked Dr Mackie to look for common denominators between the botch-ups, to see whether any lessons could be learned, but she did not know how long that would take.
"I'm looking for answers to prevent this happening again."
Street said that wasn't good enough: "We can't go another six months and have another poor woman suffer like this."
