Cancer risk lurks behind 'normal' result

Mammograms can miss up to 50% of breast cancers in women with dense breast tissues

Both dense breast tissues and cancerous tissues appear white on the mammogram, so the cancerous ones are often masked by the dense ones, says Dr Esther Chuwa, a consultant breast surgeon at Gleneagles Hospital.
Both dense breast tissues and cancerous tissues appear white on the mammogram, so the cancerous ones are often masked by the dense ones, says Dr Esther Chuwa, a consultant breast surgeon at Gleneagles Hospital. ST FILE PHOTO

The patient was clearly anxious. Despite a mammogram showing that she had no breast cancer, she was not reassured.

"My right breast doesn't feel quite right. I just want to be doubly sure," said the 44-year-old lawyer.

This was three months after her mammogram. ?

  • Dense breast tissue: Some options

  • There is no definite consensus about what women should do if they are reported to have dense breast tissue. But they should consult their doctors to assess other risk factors, such as family history and previous breast biopsy results, before deciding whether supplemental imaging is necessary.

    If there is a very high risk, such as having the BRCA-gene mutation, then a magnetic resonance imaging (MRI) scan needs to be done in addition to mammography, said Dr Jill Wong, a senior consultant at the division of oncologic imaging at the National Cancer Centre, Singapore.

    If there is no family history or significant medical history, they may need only a physical examination, on top of mammography.

    In the United States, some doctors advocate supplemental ultrasound scans. But these have several drawbacks - they tend to find a lot of abnormalities that are not cancer and lead to unnecessary biopsies, said Dr Wong.

    Yet others do tomosynthesis, which creates a three-dimensional picture of the breast using X-rays.

    Each extra modality adds cost and some add radiation exposure to the screening process, said Dr Wong. Many of these supplemental procedures will find additional abnormalities which may require biopsies that are often negative for cancer, she said.

    Despite the lack of statistical evidence to routinely recommend additional ultrasonography or MRI scans, women with dense breasts or significant additional risk factors should be made aware of, and offered, additional options, said Dr Esther Chuwa, a consultant breast surgeon at Gleneagles Hospital.

    But as far as cancer screening is concerned, mammography remains the best method.

    It is the only test that has been proven to be useful for screening, said Dr Chan Ching Wan, a senior consultant at the division of surgical oncology (breast surgery) at the National University Cancer Institute, Singapore (NCIS).

    It detects life-threatening disease at an earlier, more curable stage.

    While 15 per cent of cancer cases are not detectable by this method, no other method has been shown to be better in terms of economy, efficiency as well as rates of detection, said Dr Chan. It is also fast. Reports can be out in two hours.

    The recently developed three-dimensional imaging technique - tomosynthesis - can potentially improve the accuracy of mammography, by reducing overlapping shadows from breast tissue. Studies have shown that this technique decreases recall rates - when patients are asked to return for further tests due to an abnormal mammogram.

    It is better at differentiating between worrying and benign lesions, without a decrease in the number of cancer cases found, said Dr Chan. NCIS will be getting this machine at the end of this year, she added.

    Breast cancer is currently the most common cancer among women in Singapore, with more than 9,200 women diagnosed with the disease between 2010 and 2014.

    Yet a recent study found that half of women here go for a mammogram only when they have symptoms. The study was carried out by doctors from Changi General Hospital's Breast Centre @ Changi on more than 1,000 women. The study also revealed that women here have poor knowledge about screening mammograms. They are unaware of the appropriate age to begin screening, despite having good general knowledge about the disease.

    Ng Wan Ching

Because she was insistent and obviously unsettled, Dr Esther Chuwa decided to do an ultrasound scan at her area of concern. Suddenly, where there was nothing before, a barely visible 1.5cm area of distortion appeared, ominously lying within the depths of her nodular tissues.

A biopsy confirmed it was Stage 2 invasive breast cancer, said Dr Chuwa, a consultant breast surgeon at Gleneagles Hospital.

The tumour was nearly 3cm in diameter. It was surgically removed and the patient underwent chemotherapy earlier this year.

None of this had been evident on her last mammogram, due to "dense" breast tissue.

She is among the 15 per cent of women here who have mammograms that miss detecting their breast cancer.

This is also a worldwide statistic, said Dr Chan Ching Wan, a senior consultant at the division of surgical oncology (breast surgery) at National University Cancer Institute, Singapore (NCIS).

In addition, mammograms can miss up to 50 per cent of breast cancers in women with "extremely dense"? breasts, said Dr Chuwa.

Research suggests that women with dense breasts are also six times more at risk of developing breast cancer in their lifetime, she said.

Herein lies a double jeopardy.

Women with dense breast tissues have a higher risk of breast cancer, but a lower chance of having the cancer detected by a mammogram alone, said Dr Chuwa.

Breast density is determined by factors such as hormone levels, age and ethnicity. Generally, Asian breasts are smaller and denser than Caucasian breasts.

One study cites that 57 per cent of the women in the Asian population have dense breasts, compared with 44 per cent in the Caucasian population, said Dr Jill Wong, a senior consultant at the division of oncologic imaging at National Cancer Centre, Singapore (NCCS).

Dense tissues appear white on the mammogram while fatty tissues appear dark, said Dr Chuwa.

But cancerous tissues also appear white, and are therefore often masked by dense tissues, she said.

Density is measured on a four-point scale - a score of one indicates predominantly "fatty", less dense breasts; while four means "extremely dense".

There are also some large cancerous lumps which the woman may be able to feel but which may blend in with the normal tissue, said Dr Wong.

It is important for women, if they can feel breast lumps, to report these to their doctors even if their mammograms appear normal, she said.

The doctor can then use other tests to determine if there is cancer.

That was the case with Mrs Y. P. Tan, 42, a financial controller. She had always had "lumpy" breasts.

In her early 30s, she had a mammogram to rule out cancer.

Two years ago, she had a full body check-up which included a mammogram. Again, the result was clear.

But a year later, she discovered a distinct lump in her left breast, which felt different from just having "lumpy" breasts. She also felt pain in that area.

She quickly sought out a doctor.

Dr Chuwa did an ultrasound scan which picked up an area of abnormality. Mrs Tan then went for a biopsy which confirmed that she had Stage 2 breast cancer.

She had chemotherapy for six months, which shrank her 3cm-diameter tumour, before having a lumpectomy, a breast lump removal procedure. "Now, when I go for my annual check-ups, I do both a mammogram and an ultrasound scan."

But the use of ultrasound to detect breast cancer, as an additional screening tool on top of mammograms, is controversial, say doctors.

Some studies concluded that ultrasonography substantially increases cost while producing only small benefits.

A recent study found that four breast cancer deaths would be averted for every 10,000 women screened by ultrasonography, said Dr Chuwa. This small number is not viewed to be cost-effective.

There may also be heightened anxiety when non-cancerous lumps are detected from the ultrasound scan. This may lead to unnecessary biopsies and even mastectomies.

However, this has to be balanced against the obvious benefits of early detection of cancer, which could potentially increase survival of the patient and reduce the spiralling costs of treating a more advanced and widespread cancer at a later time.

For Alice (not her real name), a 48-year-old mother of three, an additional ultrasound scan could have caught her cancer earlier.

About two years ago, the yoga instructor felt a "thickening" in her right breast. But her annual mammograms, which she started going for at the recommended age of 40, had been normal.

She was reassured by doctors that nothing was wrong. Her "lumpy" breasts were attributed to muscle strain.

When she finally saw a specialist about the "thickening", an ultrasound scan revealed multiple suspicious areas in her right breast.

Further tests confirmed that cancer had spread to her lungs and bones. She had Stage 3 breast cancer. Her extremely dense breasts had masked the aggressive cancer pervading her body.

It had probably been there all along, hidden in her "normal" mammograms, said Dr Chuwa.

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A version of this article appeared in the print edition of The Straits Times on October 27, 2015, with the headline Cancer risk lurks behind 'normal' result. Subscribe