Mammogram 

Updated: Jan 21, 2022
Author: Muhammad Neaman Siddique, MBBS; Chief Editor: Eugene C Lin, MD 

Overview

Background

Although various radiographic modalities are readily available to identify lesions that are suspicious for breast cancer, mammography remains the mainstay of breast cancer screening. The role of breast sonography is confined mainly to the diagnostic follow-up of a mammographic abnormality because it may help clarify features of a potential lesion. The role of magnetic resonance imaging (MRI) for breast cancer screening is still evolving; currently MRI screening, in combination with mammography, is reserved for the screening of high-risk patients only.[1, 2, 3, 4]

In 2022, an estimated 290,560 new cases of invasive breast cancer are expected to be diagnosed—287,850 in women and 2710 in men—along with an estimated 51,400 cases of in situ breast cancer in women. Approximately 43,250 women and 530 men are expected to die from breast cancer in 2022.[1]

 Incidence rates of invasive female breast cancer have been increasing by about 0.5% per year since the mid-2000s. In contrast, overall breast cancer death rates decreased 42% from 1989 to 2019, because of both improvement in treatments and earlier detection.[1]

The lifetime risk of a woman being diagnosed with breast cancer is 12.9%, or more than 1 in 8.[5]  Due to the magnitude of the disease, its psychosocial impact, and associated morbidity and mortality, screening for early diagnosis forms a pivotal part of the struggle against this cancer.

According to the National Health Interview Survey, about 70% of women age 45 to 74 year have had a mammogram within the past 2 years. Breast cancer screening rates were higher in non-Hispanic white (71.7%) and non-Hispanic black (72.9%) women compared with non-Hispanic Asian (67.0%) and Hispanic (66.3%) women.[6]

According to the U.S. Preventive Services Task Force, the number of breast cancer deaths averted by screening and early treatment increases with age: over a 10-year period, screening 10,000 women aged 60-69 years will result in 21 fewer deaths from breast cancer; 8 fewer deaths in 10,000 women 50-59 years; and 3 fewer deaths in 10,000 women 40-49 years.[4]

Indications

In studies, mammography has clearly been shown to increase the detection of breast cancer at an earlier stage.[7] Based upon consistent data from multiple randomized trials, a strong consensus has been developed in favor of routine screening mammography for all women aged 50-69. Consensus, however, is not as strong in favor of routine screening among women aged 40-49 or women over the age of 70, and on how frequently these patient populations should be screened.

Based upon pooled data from 8 trials, the U. S. Preventive Services Task Force (USPSTF) has given an estimate that 1904 women aged 39-49 (95% credible interval [CrI], 929 to 6378 women) would need to be screened to prevent one death from breast cancer after at least 11 years of observation, compared with 1339 women in their 50s (CrI 322-7455) and 377 women in their 60s (CrI 230-1050).[8] Moreover, false-positive readings are more common in younger women, both because the tests are less specific and because breast cancer occurs less commonly in that population.[9, 10]

Recommendations for mammography by the American Cancer Society (ACS) include the following[2, 3] :

  • Women with an average risk of breast cancer should undergo regular screening mammography starting at 45 years of age.
  • Women 45-54 years of age should be screened annually.
  • Women ≥55 years should transition to biennial screening or have the opportunity to continue screening annually.
  • Women should have the opportunity to begin annual screening between the ages of 40 and 44 years.
  • Women should continue screening mammography as long as their overall health is good and they have a life expectancy ≥10 years.
  • The ACS does not recommend clinical breast examination for breast cancer screening among average-risk women at any age.

Recommendations for mammography by the USPSTF include the following[4] :

  • The USPSTF recommends biennial screening mammography for women aged 50-74 years of age.
  • The decision to start screening mammography in women prior to age 50 years should be an individual one.
  • Women who place a higher value on the potential benefit than the potential harms may choose to begin biennial screening between the ages of 40 and 49 years.
  • Current evidence is insufficient to assess the balance of benefits and harms of screening mammography in women aged 75 years or older. 

A study of screening mammography beyond age 75 years, using data from the Surveillance, Epidemiology, and End Results (SEER) program and Breast Cancer Surveillance Consortium, concluded that although annual mammography is not cost-effective, biennial screening mammography to age 80 years is. The absolute number of deaths averted is small, however, especially for women with comorbidities.[11]

 

Technique

Approach Considerations

Screening versus diagnostic

Diagnostic mammography is performed in women who present with breast symptoms such as nipple discharge or focal pain, who have abnormal clinical findings such as a palpable lump, or who have mammographic abnormalities detected on a screening study. It is performed under the direct supervision of a radiologist who chooses different additional views to further demonstrate the morphology of the lesion and decides whether ultrasound also needs to be used. Additional views include cleavage view, tangential view, and rolled view.

Breast implants

Breast implants were approved by US Food and Drug Administration in 1962. Over two million breast implants are estimated to be in US women for the purposes of either cosmetic augmentation or reconstruction.

Women with breast reconstructions with no underlying breast tissue do not require mammographic screening, whereas women with breast augmentations performed with implants do require routine screening to evaluate the native breast tissue. As implant contents are radio-opaque, small lesions may be obscured. Moreover, in patients with breast implants, evaluating all parts of the breast becomes harder because breast compression becomes difficult with implants, particularly in prepectoral or retroglandular implants. Therefore, after obtaining the standard craniocaudal (CC) and mediolateral oblique (MLO) views in women with breast implants, both views are repeated with the implant displaced back against the chest wall and breast tissue pulled forward. Prepectoral or retroglandular implants are sometimes difficult to displace. Tangential views are obtained in such cases, to attempt to adequately image the whole breast tissue.

Postmastectomy myocutaneous breast reconstruction

Mammography of a reconstructed breast is a technically feasible study, and mammographic appearance of recurrences is similar to those in native breasts. Mammography has been found useful in differentiating a true recurrence from postoperative fat necrosis that may also present as a lump. However, evidence in favor of routine imaging for asymptomatic women with myocutaneous breast reconstruction is contradictory. Currently, clinical breast examination is the method of choice for screening in these women.

Women with prior breast biopsy

Mammography in women with a history of a prior breast biopsy that diagnosed a benign disease has been shown to have a lower specificity and a lower positive predictive value for a referral for a subsequent breast biopsy compared with women with no history of prior biopsy.

Increased breast density

The presence of dense breast tissue not only poses difficulty in reading the mammogram, but it has been recognized as an independent risk factor for breast cancer.[12]  In addition, an increase in breast density over time is significantly associated with increased risk of breast cancer, while  decreases in breast density is associated with decreased risk; thus, serial measurements of breast density may provide more accurate predictions of breast cancer risk.[13]  Even though breast density represents a lower risk than other risk factors such as family history, it is more common in the general population. Thus, breast density alone accounts for a considerable proportion of cancer risk at the population level.[14]

 Digital mammography has been found out to be more sensitive in women with dense breasts and should be preferred over film mammography to screen these women (see the image below).[15]

Normal mammograms in a 40-year-old woman show dens Normal mammograms in a 40-year-old woman show dense breast parenchyma.

Pregnancy and lactation

Breast cancer in pregnant women accounts for 3% of all breast cancers. Mammography is performed in pregnant women for diagnostic purposes only, usually in settings where a sonographic examination is unable to sufficiently clarify physical findings. A mammogram comprising 4 views that is done with abdominal shielding exposes the fetus to 0.4 rads. As fetal exposure to radiation is concerning, especially during the first few weeks of gestation, routine screening mammograms are not performed during pregnancy.

Males

Men undergo mammography to evaluate for a breast mass, thickening, or pain. The initial study consists of bilateral CC and MLO views; additional views may subsequently be performed to further elaborate any abnormalities found on standard views. Breast compression is required in men also, and narrower paddles prove more helpful.

Mammographic Examination

Routine mammography consists of craniocaudal (CC) and mediolateral oblique (MLO) views. Applying an adequate degree of breast compression  before shooting the x-rays helps increase the image contrast by reducing motion artifact and enhancing the x-ray penetration. Acquiring 2 views is imperative in order to adequately image the whole breast tissue. Besides this, two views help in distinguishing a true abnormality from an overlapping structure. Studies have clearly established higher sensitivity and lower recall rates with 2 views. This benefit is generally believed to outweigh the risk associated with extra radiation from the second view.

The radiation dose absorbed by the breast depends on breast tissue thickness, increasing with the thickness of the breast. The American College of Radiology recommends that the mean radiation dose exposure in a breast tissue measuring 4.2 cm should not exceed 0.3 rads per image. Accounting for the relative sensitivity of breast tissue to radiation exposure, the effective radiation dose received by the breast during a routine screening examination proves to be approximately equivalent to the natural background radiation exposure cumulatively acquired over a 3-month period (ie, 0.7 millisievert units). Women who have BRCA1 or BRCA2 mutation and thus have impaired DNA repair mechanisms are at higher risk for radiation-induced carcinogenesis compared with women who do not have these mutations. However, keeping the radiation dose as low as possible in all women is important.

A digital mammography system tends to require a lower radiation dose than film screen mammography for the same image quality. Digital detector converts the x-ray photons to an electronic signal, which is further processed and displayed as a gray scale image. This image can either be electronically sent to a viewing station and displayed on a high-resolution monitor or printed and read on luminant-view boxes similar to how film screen mammograms are read.

The digital system provides greater contrast resolution and thus better visualization of skin, peripheral breast tissue, and dense breasts. Besides this, it allows for changes in zoom, contrast, and brightness, which increase the ability to detect subtle abnormalities.

A film screen system does not offer such facilities and also tends to suffer from artifacts during processing and storage. These deficiencies are, however, partly compensated for by the advantage of a higher spatial resolution in film screens than in digital systems. However, despite all those technological differences, studies have shown that the overall diagnostic accuracy was similar with these 2 modalities except for premenopausal and perimenopausal women, in whom digital mammography was found to be more accurate.[16] This is at least partly because digital mammography is relatively more sensitive than film mammography in detecting cancer in dense breasts.

Mammogram Reporting

Mammographic features that identify abnormal breast tissue are asymmetry, architectural distortion, and calcifications. Calcifications may represent benign or malignant lesions. Linear and branching calcifications have a higher predictive value for malignancy compared with granular ones. Calcifications have been associated with higher grade, smaller size lymph node positive, hormone receptor—negative, and human epidermal growth factor receptor 2 (HER2)–positive tumors.[17]

The most specific mammographic feature of malignancy, however, is a spiculated soft tissue mass; nearly 90% of these lesions represent invasive cancer. Clustered microcalcifications (calcium particles 0.1-1 mm in diameter and numbering more than 4-5 per cubic centimeter) are found in about 60% of mammographically detected cancers. Skin thickening, increased breast density, and coarsening of stroma may be detected in patients with inflammatory breast cancer.

The following forms of calcifications  are all considered benign:

  • Smooth round or oval calcifications
  • Rim-like calcifications
  • Large coarse calcifications
  • Vascular calcifications
  • Cigar or rod-shaped calcifications
  • Multiple coarse "popcorn" calcifications

See the images below.

Screening mammogram depicts malignant ductal-type Screening mammogram depicts malignant ductal-type microcalcifications.
Image shows a malignant-type lesion: an invasive d Image shows a malignant-type lesion: an invasive ductal carcinoma. This stellate (spiculated) lesion has ductal-type microcalcifications.
Image shows a benign lesion: a fibroadenoma with w Image shows a benign lesion: a fibroadenoma with well-defined edges and a halo sign.
Benign microcalcifications: cystic hyperplasia. Benign microcalcifications: cystic hyperplasia.
Breast cancer, mammography. Bilateral mammogram sh Breast cancer, mammography. Bilateral mammogram shows diffuse inflammatory carcinoma of the left breast.

Double Reading

Double reading means that the mammogram is read by 2 radiologists, either independently or together. This is a standard practice in Europe, but not in the United States. The aim is to increase the sensitivity and specificity of the examination. If the readers happen to differ in their interpretation of a mammogram, the issue can be approached in 3 different ways:

  • "Highest reader recall”–The patient is called back for follow-up studies if either of the radiologists identifies an abnormality.
  • "Arbitration” – A third reader reviews the films and determines whether the patient needs further diagnostic work-up.
  • "Consensus” – A panel of radiologists,  which may or may not include the original readers, revews the films and decides on a course of action.

Many observational studies have shown benefit for double reading, but no randomized trials have studied the practice. A data review from the Norwegian Breast Cancer Screening Program for over a million examinations that were performed by radiologists, 50% of whom were dedicated mammography readers, found that 23.6% of the cancers detected were diagnosed in patients who were recalled for discordant interpretation.[18]

Computer-Aided Detection

Computer-aided detection (CAD) is a computer-based technology that helps radiologists identify suspicious areas in digitalized mammograms. It was approved by the US Food and Drug Administration (FDA) in 1998. No randomized trials have been performed to assess its effect on breast cancer mortality. A meta-analysis showed a small, statistically insignificant increase in cancer detection rate, but this was associated with a higher recall rate and more false-positive readings.[19]

The Report

Prior to describing any abnormalities, the report gives out the indication for the study, the breast density in percentage, and whether the examination was a screening or a diagnostic procedure.

Abnormalities are reported using the standard Breast Imaging–Reporting and Data System (BI-RADS) descriptors. The location(s) of the lesion(s) are described with reference to a quadrant or clock position, and the depth within the breast. Each breast is arbitrarily divided into 4 quadrants: upper-inner, upper-outer, lower-inner, and lower-outer. In terms of depth, the breast is divided into anterior, middle, or posterior.

All mammograms are classified into one of the standard BI-RADS categories, based upon the presence or absence of various mammographic abnormalities. The BI-RADS categories are defined as follows:

  • BI-RADS 0: The assessment is incomplete. Additional imaging evaluation (further mammographic views and/or an ultrasound) and/or prior mammograms for comparison are needed.

  • BI-RADS 1: This is a completely negative examination. The woman should continue with screening mammography and clinical breast examination based on screening guidelines.

  • BI-RADS 2: This represents benign findings such as cysts, fibroadenomas, or benign vascular or parenchymal calcifications. Malignancy is not a concern, and routine follow-up is recommended.

  • BI-RADS 3: This represents findings that do not have characteristic benign features, but the likelihood of malignancy is less than 2%. Examples of such findings are parenchymal asymmetry, calcifications, or a nodule that does not have classic benign imaging features. These patients are advised to have follow-up studies at shorter intervals, during which the category may be upgraded if lesions change sufficiently to raise concern for a malignancy or be downgraded if repeated imaging confirms benignity of the lesion.

  • BI-RADS 4: This represents findings that are suspicious for malignancy.

  • BI-RADS 5: This represents lesions that are highly suggestive for malignancy, such as spiculations, pleomorphic calcifications, and skin retraction.

  • BI-RADS 6: This represents biopsy-proven malignancy in which the mammogram is being performed to either evaluate the contralateral breast or assess response to neoadjuvant chemotherapy.

Digital Tomosynthesis

Digital breast tomosynthesis (DBT), or 3-dimensional (3-D) mammography, is a further advancement of digital mammography. It was approved by the FDA in 2011.[1]  In DBT, a 3-dimensional digital data is acquired with the help of a moving x-ray source and a digital detector and is further processed using computer algorithms to generate thin-section images. This 3-dimensional reconstruction improves the demarcation of a lesion by reducing the overlap from surrounding structures. Available data suggest that this technique may improve both the sensitivity and specificity of mammographic detection of cancer. However, it requires longer radiation exposure and there remains a concern for increased risk of motion artifact.[20]

In a British study, two-view mammography with one-view DBT showed significantly higher accuracy in assessing mammographic abnormalities, compared with two-view mammography and coned compression magnification mammography (CCMM). According to the authors, these results showed that DBT can help evaluate mammographic screening abnormalities.[21]

Although DBT has higher accuracy than digital mammography, the interpretation time is substantially longer. Shoshan et al reported that an artificial intelligence model was able to identify normal DBT screening examinations, thus decreasing the number of examinations that required radiologist interpretation.[22]

Halal et al suggested that the accuracy of breast cancer staging can be improved by combining DBT with contrast-enhanced spectral mammography (CESM). In their study of 98 women with histologically proven breast cancer, DBT was more accurate for assessing tumor size (70.4%) compared with CESM ( 50%) or regular digital mammography (60.2%) but CESM was most sensitive in the detection of multiplicity (92.3%), followed by DBT (77%) and regular mammography (53.8%).[23]

For further information on digital tomosynthesis see 3D Mammography.

 

Questions & Answers