by Dr. Wong Siong Lung

Consultant Radiologist MD (UKM), M.MED (Radiology) (UKM), AM (Mal), PGDip (UNIMAS)

Clinicians and patients alike are sometimes puzzled with the choice of either ultrasound or mammogram as a first line screening tool for early breast cancer detection. In this article, the advantages and shortcomings of these modalities are discussed. What can mammogram detect?

Women undergoing screening for breast cancer should consider mammogram as the first choice of investigation. This is because mammography is excellent in the detection of microcalcifications as seen in DCIS (ductal carcinoma in situ), an early manifestation of breast cancer. DCIS may turn into invasive cancer in up to 50 percent of patients within the period of 10 years. Ultrasound scan is not as sensitive in picking up microcalcifications as with mammography study. Hence ultrasound is not suitable as first line choice of investigation for DCIS.

If mammogram is so good, why need ultrasound?Another important finding to look out for on mammogram is the presence of a mass. If a mass or nodule is detected, it will be shown as a “white” shadow. Mammography can assess the margins of the lesion, the degree of ‘whiteness” (density) of the lesion, presence of spicules and architectural distortion. However, many Asian women have very dense breasts, i.e. very thick glandular tissue. Hence the normal glandular tissue can obscure the mass lesion as both normal glandular tissue and mass lesion appear as white area on mammogram. Therefore patients with dense breasts are routinely offered complementary ultrasound to exclude mass lesion.

Can thick glandular tissue hide the microcalcification in DCIS?Fortunately dense breasts do not hide the microcalcifications on mammogram, thus is not a concern for missing DCIS. When should screening commence?Women reaching the age of 40 should be offered annual screening mammography. It is vital to screen as early as possible as breast cancer occurs in younger Asian women than the Caucasians .

Range of breast density in mammogram Amount of fibroglandular tissue dictates the density of mammograms, shown here from very dense (far right) to very fatty (far left). Fatty breast density enables easy detection of masses while very dense breast may obscure small masses, necessitating ultrasound correlation.

KPJ Sibu Specialist Medical Centre