SINGAPORE - At least 200 patients were wrongly diagnosed by Khoo Teck Puat Hospital (KTPH), with a more aggressive form of breast cancer than they actually had.
Some were given unnecessary treatment that likely cost tens of thousands of dollars for each of them.
The results of a retest for eight patients are still pending.
On Dec 11, the KTPH disclosed that about 180 patients had been wrongly diagnosed with HER-2 positive breast cancer, and that it was reviewing tests done since 2012.
HER-2 is a less common form of breast cancer and generally affects 15-20 per cent of such patients. There are drugs targeted at this particular form of cancer, the first and most commonly used being Herceptin.
Replying to questions in Parliament from several MPs on Monday (Jan 4) on the side effects patients may have suffered, Dr Koh Poh Koon, Senior Minister of State for Health, said common side effects are diarrhoea, chills and fatigue.
About 3-4 per cent of patients may suffer heart problems.
Doctors are reaching out to affected patients to help them and to assess any side effects due to the drug, he said.
Ms Cheryl Chan (East Coast GRC) asked why it took so long for the error to be discovered.
Dr Koh replied that 6 per cent of patients globally are wrongly diagnosed as having HER-2 positive breast cancer. The test is highly complex and without a definitive answer.
He said it takes a trained pathologist to make a judgment on the test result. But this could be affected by the multiple steps that require human intervention, such as the concentration of stains and how the tissue was handled.
It requires a fairly large number of results to trigger an alert on the possibility of a disproportionate number of patients being diagnosed with the condition.
Dr Koh said the mistakes were discovered because of the "institutional process". The hospital's tumour board flagged that the number of HER-2 positive cases was higher than normal, leading to the review.
He added that reviews were done for patients diagnosed as having HER-2 positive breast cancer since 2012 because that was when the hospital first started doing such tests, and not because errors had occurred then.
Dr Lim Wee Kiak (Sembawang GRC) and Dr Tan Wu Meng (Jurong GRC) asked about the additional cost incurred by affected patients. Dr Tan, a cancer specialist, suggested that compensation take into account the time taken from work by a patient or caregiver for the unnecessary treatment.
Dr Koh said it was difficult to give a figure as the cost varies with individual patients. Furthermore, he said not all the 200 patients who were wrongly diagnosed were given Herceptin. Some, he said, may have been too frail.
The KTPH had earlier said "about half of these patients may have received unnecessary treatment for HER2, usually the drug Herceptin".
The Straits Times understands that Herceptin costs $3,000-$4,000 per cycle in the public sector, and about $5,000 in the private sector. Eight of the patients given the wrong diagnosis were treated in private hospitals.
Patients are usually treated for a year, and undergo 17 to 18 cycles. This comes to $50,000 to $70,000 per patient in the public sector.
"The portion of the bills which arose from the unnecessary treatment will be fully refunded," said Dr Koh.
Even discounting the subsidy that some of these patients had received, the refunds will likely total millions of dollars.
Dr Koh also noted that "the preferred state" for cancer is over rather than under treatment, adding that not having HER-2 positive cancer means patients have better prognosis.