SUMMARY: Breast cancer is the most common cancer among women in the US and about 1 in 8 women (12%) will develop invasive breast cancer during their lifetime. Approximately, 231,840 new cases of invasive breast cancer will be diagnosed in 2015 and over 40,000 women will die of the disease. Screening mammography complemented by breast self exam and clinical breast exam has resulted in early detection of breast cancer and successful outcomes. Even though mammography is a sensitive screening test, a small percentage of breast cancers may not show up on mammograms but may be palpable on examination by the patient or the clinician. Further, mammograms are less likely to find breast tumors in younger women with dense breast tissue. The following is a brief overview of the imaging techniques for breast cancer screening
Mammography
Mammography is performed by compressing the breast firmly between two plates and utilizes ionizing radiation to image breast tissue. During routine screening, breast tissue from the nipple to the pectoral muscle in the mediolateral oblique and craniocaudal views, is included. The radiation exposure is 4 to 24 mSv per standard two view screening examination. Two view screening is associated with a lower recall rate and lower interval cancer rates than are single-view exams. Breast Imaging Reporting and Data System (BI-RADS) categories are used for reporting mammographic results as follows:
0: Incomplete—needs additional image evaluation and/or prior mammograms for comparison.
1: Negative.
2: Benign.
3: Probably benign.
4: Suspicious.
5: Highly suggestive of malignancy.
6: Known biopsy—proven malignancy.
A digital mammogram is more expensive than screen-film mammography (SFM) and the data can be stored and shared. Compared with film mammography, sensitivity is higher for digital mammography, particularly in women younger than 50 years, but the specificity is either the same or lower than film mammography.
Computer-Aided Detection (CAD) systems increase detection of ductal carcinoma in situ (DCIS) by highlighting suspicious regions in the breast such as clustered microcalcifications and masses in mammograms. There is however no improvement in invasive cancer detection rate and there is an increase in recall rate.
Tomosynthesis
Tomosynthesis, or 3-Dimensional (3-D) mammography involves multiple short-exposure x-rays, from different angles and a three dimensional image is created for better visualization. A combination of 2-D and 3-D mammography has been reported to be more accurate than 2-D mammography alone, with the caveat that the radiation exposure to the patient is essentially doubled. Tomosynthesis in the diagnostic setting is at least as effective as spot compression views, for workup of non-calcified abnormalities, including asymmetries and distortions and may decrease the need for ultrasound testing.
Ultrasonography
Primarily utilized for the diagnostic evaluation of palpable or mammographically detected masses and distinguish solid tumors from cysts. It is a helpful adjunct modality in women with dense breast tissue. Images are created using high frequency sound waves with no radiation exposure. Evidence is lacking to support the use of ultrasound instead of mammography, at any age, in population based breast cancer screening.
Thermography
Thermography uses infrared imaging techniques and identifies temperature changes in the skin as an indicator of an underlying tumor. These changes are displayed in color patterns. The impact of thermography on breast cancer detection or mortality, has not been evaluated in randomized clinical trials and there appears to be no additional benefit for the use of thermography as an adjunct modality, for breast cancer screening.
Magnetic Resonance Imaging
Magnetic Resonance Imaging (MRI) is more sensitive than mammography although the specificity of a breast MRI is lower, resulting in a higher rate of false-positive findings and potentially unnecessary biopsies. Microcalcifications in the breast can be missed by a breast MRI. The American Cancer Society (ACS) recommends an annual MRI as an adjunct to screening mammogram and clinical breast exam in certain groups with increased risk of breast cancer. They include individuals with deleterious genetic mutations such as BRCA1/2 mutation carriers, a strong family history of breast cancer, or several genetic syndromes such as Li-Fraumeni or Cowden disease. MRI may also be used to evaluate the integrity of silicone breast implants, assess palpable masses following surgery or radiation therapy, detect mammographically and sonographically occult breast cancer in patients with axillary nodal metastasis and preoperative planning for some patients with known breast cancer. Breast MRI is performed preferably between days 7-15 of menstrual cycle for premenopausal women, using a dedicated breast coil, with the ability to perform a biopsy under MRI guidance by experienced radiologists, during the same visit.
Molecular Breast Imaging
Molecular Breast Imaging (MBI) involves the injection of technetium-99m (Tc-99m) sestamibi, a radioactive substance, which then allows tumor visualization with a gamma camera. MBI along with mammography significantly increased the cancer detection rate in women with mammographically dense breasts, compared to mammography alone, in a recent study. This new technology is not yet widely available.
References: 1) American Cancer Society recommendations for early breast cancer detection in women without breast symptoms. http://www.cancer.org/cancer/breastcancer 2) National Cancer Institute: PDQ® Breast Cancer Screening. Bethesda, MD
