Is an ultrasound as good as a mammogram for breast cancer screening?

Breast cancer is on the rise in Singapore like it is in the rest of the world. Every year, as many as 1,500 women, or about four women every day, are diagnosed with breast cancer in Singapore, making it the most common cancer among women here.

To catch the cancer early, women aged 50 and above should go for a breast screening once every two years, and those between the ages of 40 and 49 should consider an annual screening.

Mammograms and ultrasounds are commonly used to detect breast cancer. However, the mammogram is the primary screening tool for women who display no symptoms of the disease.

Ultrasound vs mammogram

As an ultrasound is less painful than a mammogram, many women ask: Could I have an ultrasound instead of a mammogram to screen for breast cancer?

According to Dr Teo Sze Yiun, Senior Consultant and Head of the Breast Imaging Unit, Department of Diagnostic and Interventional Imaging, KK Women's and Children's Hospital (KKH), the answer is "No". She explains, "A breast ultrasound should not be compared to a mammogram as these are two different imaging modalities with different functions. An ultrasound does not replace a mammogram or vice versa. ."

A breast mammogram has been shown in multiple studies to be the only screening tool to decrease the number of deaths from breast cancer.

Related article: A patient explains how a mammogram helped save her life -- twice

What is a mammogram?

A mammogram, a screening tool that has been around since the 1960s, uses low-dose
x-rays to examine the breasts. Its aim is to detect early breast cancer when the chance of a cure is the highest.

The mammogram works by compressing the breasts for a few seconds so that two standard images — one vertical and one horizontal — can be taken of each breast. The breast compression is necessary to:

• Immobilise the breast

• Flatten and spread the tissue so that small abnormalities are not obscured

• Give the clearest image

"All these factors lead to a good quality mammogram which is essential for an accurate diagnosis," says Dr Teo.

Related video: What to eat to help prevent cancer

Is the radiation from a mammogram harmful?

"The benefit of early breast cancer detection far outweighs the small amount of radiation," explains Dr Teo. "The dose of radiation is very small and has minimal scatter to other parts of the body."

The images from the mammogram are separately analysed by two radiologists — this double reading has been found to increase the cancer detection rate. If the findings are uncertain, a woman may be called for further tests which include extra mammographic views and a breast ultrasound.

"About 5-10 per cent of women are asked to return for further tests. Typically, 90 per cent of these further tests indicate normal or benign (not suspicious) results," says Dr Teo.

Benefits of a mammogram

• A mammogram is able to detect microcalcifications, which are tiny dots of calcification seen in early breast cancer.

• Studies have shown that cancers detected during screening have a favourable outcome compared to clinically detected cancers, which is breast cancer that can be felt as a lump on clinical examination.

• Early breast cancer is curable with cure rates approaching 100 per cent.

Related article: What are the 10 most common cancers in men and women in Singapore?

When a mammogram is not effective

"A mammogram is not fail-proof and a small number of breast cancers may be hidden from view on mammography," says Dr Teo.

Some women also have very dense breasts which make it difficult to detect small abnormalities. Because of these factors, a mammogram can detect about 90 per cent of breast cancers.

What is an ultrasound?

Women who require further testing may be sent for an ultrasound which is a medical imaging test that uses high speed sound waves to assess the tissues inside the body. The sound waves are converted into pictures which are then analysed by a technologist. Since it does not employ x-rays, an ultrasound is safe for pregnant women.

A breast ultrasound examination, in which a small hand-held probe is moved across the breasts, lasts for about 10-30 minutes. It is useful for the following reasons:

• It evaluates the cause of breast symptoms such as a lump, swelling, breast pain.

• It determines if the lump is filled with fluid (a cyst) or is solid.

• It adds information to other tests such as a mammogram or a breast MRI.

• It helps guide the placement of needles for procedures such as a biopsy.

"If a breast lump is present, an ultrasound study may be able to accurately distinguish a benign lump from a cancerous one most of the time," says Dr Teo. "Sometimes, in addition to the ultrasound, a biopsy may be needed to confirm that a lump is benign."

Bottom line: While having its own advantages, a breast ultrasound is not useful for detecting the microcalcifications seen in early breast cancer, says Dr Teo. It is best used for the evaluation of a breast lump or other breast symptoms.

Women aged 40 and above are advised to undergo a regular screening mammogram.

Related article: Having your first child after the age of 30 is a risk factor for breast cancer: True or false?

This article was written by Anjana Motihar Chandra for Health Xchange, with expert input from Dr Teo Sze Yiun, Senior Consultant and Head, Breast Imaging Unit, Department of Diagnostic and Interventional Imaging, KK Women's and Children's Hospital

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