By Dr. Dennis Tan Gan Pin
MBBS (Malaya), M. Med. Radiology (Malaya)
Breast cancer is the third most common cancer worldwide, and the most common cancer among women. It comprises about 30% of total cancer in female, and mainly affects women between 40 to 65 years of age. Malaysian women have a 1 in 19 chance of developing breast cancer in their lifetime. Several medical imaging modalities are available for detection of breast cancer:
As the present mainstay of diagnosis at present, mammography may be performed through screening tests, such as imaging of asymptomatic women to detect early cancer, or diagnostic tests to assess women with clinical findings such as palpable lumps, bloody nipple discharge or pain.
According to American College of Radiology Practice Guideline 2013, annual screening mammography is recommended for asymptomatic women aged 40 and older. For women under the age of 40 but with an increased risk of breast cancer (e.g. known BRCA gene mutation, first degree relative with breast cancer), screening mammography is also recommended yearly beginning from the age of 30. Studies have shown that screening mammography may reduce the mortality rate of breast cancer by 17-30%.
Mammography is basically the X-ray examination of the breasts, involving a very small dose of radiation. A female radiographer performing the examination will position and compress the breasts between 2 plates of the mammography machine. This is necessary to reduce the radiation dose and to produce a clearer image. Mammography images will then be interpreted by the radiologist.
Ultrasound is another commonly-used modality to assess breast lump/cancer. It uses sound waves and does not involve ionizing radiation. During the examination, a small handheld unit known as transducer lubricated with gel is gently pressed back and forth over the breast.
Ultrasound is not routinely used for screening. It is often being used as supplementary modality to confirm or characterize mass detected on mammography, as well as examining high risk women with dense breasts on mammography. Ultrasound may be used as initial investigation tool in younger women presented with one or more breast lumps, as mammography is often suboptimal in this group of women due to their dense breast tissue.
Ultrasound is a very helpful modality to guide the biopsy of a breast lump. During this procedure, local anaesthesia will be given to numb the area. A small specimen of breast tissue is then taken from the lump using a small biopsy needle under ultrasound guidance. The specimen is sent to the laboratory where it is examined under the microscope by a pathologist. Whether the breast lump biopsied is benign (harmless) or cancerous is then determined by the pathologist.
MAGNETIC RESONANCE IMAGING (MRI)
Technological and technical advances in the field of MRI in recent years have made MRI an attractive option in diagnosis of breast cancer. MRI uses magnet and radio waves and thus, does not involve ionizing radiation. Contrast liquid (a gadolinium compound) needs to be injected into a vein during the examination to delineate the structures of the breasts.
MRI is a useful adjunct to mammography for screening women at increased risk for breast cancer. The American Cancer Society (ACS) recommends annual supplementary screening with MRI in addition to mammography in high-risk patients. MRI is currently the most sensitive modality for invasive breast cancer as MRI may detect other abnormal growths not seen in mammography. MRI is also useful in assessing the extent of cancer, detection of cancer recurrence and response to cancer therapy.
Screening mammography is a useful tool in the early detection of breast cancer and has been proven to reduce breast cancer mortality rates. For women at average risk, annual screening mammography is recommended from the age of 40. On the other hand, for high-risk women, both screening mammography and MRI are recommended to commence at the age of 30. Ultrasound is useful as a supplementary examination to mammography and for younger women with palpable breast lumps.