Faulty KTPH test: What is the HER2 test and the breast cancer type linked to it?

In Singapore, breast cancer accounts for almost 30 per cent of cancers in women.
In Singapore, breast cancer accounts for almost 30 per cent of cancers in women.PHOTO: ISTOCKPHOTO

SINGAPORE - About 90 breast cancer patients may have received unnecessary treatment since 2012 due to inaccurate test results.

Khoo Teck Puat Hospital (KTPH), which announced this on Friday (Dec 11), also estimated that 180 patients may have got the wrong test results.

Here is more about the test and breast cancer type linked to it.

What is the HER2 test?

The test which produced inaccurate results for 180 women is used to determine how aggressive a patient's breast cancer is likely to be, so doctors can offer the right treatment.

It checks for human epidermal growth factor receptor 2 (HER2) proteins, which normally regulate the healthy growth of breast tissue.

The test works by introducing antibodies tagged with a coloured dye to a sample of breast tissue. These attach themselves to HER2 proteins, which show up as a stain when a doctor observes the sample under a microscope.

The intensity of the stain determines whether the result is positive or negative.

The gene that produces the protein can cause uncontrolled tissue growth if it malfunctions.

If a breast cancer patient is HER2-positive, it means she is likely to have a tumour that is more aggressive than those in HER2-negative patients.

She will probably respond poorly to certain treatments such as standard chemotherapy or hormone therapy. The patient may be considered for HER2-specific treatments such as the drug Trastuzumab, which works by attaching itself to HER2 receptors on breast tissue cells to block them from receiving growth signals.

The drug can cause side effects such as diarrhoea, chills and fever. It can also cause heart problems in about 3 per cent to 4 per cent of patients.

What are HER2-positive breast cancers?

Breast cancer is a disease that involves abnormal cell growth in the breast, which can spread to other parts of the body and cause health problems.

It is the most common type of cancer in women internationally. In Singapore, breast cancer accounts for almost 30 per cent of cancers in women.

Breast cancers can have different characteristics requiring different treatments, depending on the presence or absence of certain receptors.

The most common form involves hormone receptors such as oestrogen receptors and progesterone receptors.

About 70 per cent of breast cancers are positive for one or both of these receptors, meaning the patient's hormones play a role in the cancer's development.

Hormone receptor-positive breast cancers tend to be less aggressive and grow more slowly. These patients are likely to see better outcomes in the long term. Treatment will typically involve hormone therapy drugs such as tamoxifen, which blocks oestrogen receptors in the breast tissue.

HER2-positive breast cancers, or those that involve the human epidermal growth factor receptor 2 (HER2) protein, are less common, affecting between 15 per cent and 20 per cent of patients.

This type of breast cancer arises when the HER2 protein, which normally regulates healthy breast tissue growth, is produced in excess. It tends to be more aggressive compared with hormone receptor-positive cancers.

Drugs which block HER2 receptors may be prescribed to such patients.

Less common are what is known as triple negative breast cancers, which do not have receptors for oestrogen, progesterone or HER2.

These cancers, seen in about 15 per cent of patients, are particularly aggressive and are associated with higher rates of relapse and lower survival rates. Treatments usually involve surgery, radiation therapy and chemotherapy.

Misidentified cancers could result in unnecessary or insufficient treatment.

A false positive could cause a patient to receive treatment she did not need, while experiencing the side effects of the drug or procedure she was given.

Meanwhile, a false negative could mean that she missed out on treatment she would have otherwise benefited from.

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