A mass is a space-occupying lesion that is seen in two different mammographic projections. It has an outwardly convex border, is seen on two views, and is at least as dense centrally as in the periphery. Summation shadows on the other hand are produced by fortuitous superimposition of fibroglandular tissue and are not visualized in more than one projection [4]. When a mass is identified on a screening mammogram, an analysis of its features is done as follows: The shape of the mass is described as being round, oval, or lobular when a mass has an undulating contour. If a mass cannot be described as one of these, it is described as having an irregular shape (Fig. 5.1a–c). Once the primary features are ascertained, recall for a diagnostic assessment is often initiated. Spot compression views help define the margin characteristics of a mass. A margin that is sharply demarcated and well defined in at least 75 % of its extent and remainder is obscured is considered circumscribed with an abrupt transition from the mass to the surrounding tissue. Small undulations of the border of a mass are defined as a macrolobulated border. A poor definition of the margin is suspicious for infiltration, a finding suggestive of malignancy. When lines radiate from the edge of a mass, the margin is described as being spiculated [5]. A mass with a density higher than of the surrounding fibroglandular parenchyma is more likely to be malignant than a low-density mass (Fig. 5.2a–c). In a retrospective study of 348 breast masses with biopsy confirmation, 70.2 % of the high-density masses were malignant, and 22.3 % of the iso- or low-density masses were malignant [6]. Similar results have been reported using inductive logic programming and conditional probabilities and validating this association in an independent dataset [7].

There is a reported association between morphologic features and tumor stage and prognosis. Masses with spiculated margins are known to be associated with lower-grade tumors and hence have a better prognosis (Fig. 5.3a, b). On the other hand triple-negative breast cancers have been found to be associated with circumscribed masses and masses with microlobulations and with ill-defined borders. Lymphovascular invasion has been reported to be seen more often in breast cancers associated with architectural distortion rather than those with spiculated mass. The reason behind this association is unknown [8]. Lymphovascular invasion is also more common in masses with calcifications. In invasive cancers, the presence of calcifications is often associated with extensive intraductal component and necrosis. In one series breast cancers presenting as architectural distortion were reported to have positive margins in 65 % of cases. These investigators, however, did not find a significant correlate between mammographic features and tumor differentiation or ER (estrogen receptor)/PR (progesterone receptor) status [8].

It is known that the proportion of invasive cancers tends to be higher in younger women (Fig. 5.4a–c). The ratio of invasive to noninvasive cancers increased from 1:1 in those younger than 50 years of age to 3:1 in those over 70 years. Breast cancers presenting with calcifications are also decreased from 63 % in women younger than 50 years to 26 % in older than 70 years [2]. Generally calcifications that are malignant are associated with DCIS in 63 % of cases, whereas a spiculated mass is associated with invasive cancer in as high as 95 % of cases [9]. In a small percentage of cases, spiculated masses may represent pure DCIS or DCIS associated with a radial scar, 8 % of a series of 86 lesions with predominant DCIS in one series [10]. The prognosis is best and 8-year survival was the longest for small spiculated masses [95 %] that are 1–9 mm and good for rounded masses [91 %] compared to those presenting with calcifications [77 %]. Patients with casting or pleomorphic calcifications had significantly worst prognosis [11].

Architectural distortion refers to a localized disruption of the breast architecture which can include spiculations or thin lines that radiate from a focal point or a localized retraction of the edge of the parenchyma at its interface with fat. It is a normal finding to see lines randomly crossing within the breast parenchyma; what is abnormal is when one sees these lines converging to a focal area. Not uncommonly overlapping crisscrossing tissue lines may simulate architectural distortion on a screening mammogram. Careful inspection alone with use of a magnifying lens may suffice to make this assertion; when unclear, recall for spot compression and rolled views of the breast in the projection where it is best seen will help to exclude an area of true architectural distortion (Fig. 5.5a, b). Architectural distortion when unassociated with other findings such as masses or clustered calcifications can be often subtle and accounts for a significant number of missed breast cancers; a discussion on missed cancers appears later. Architectural distortion is less common than a mass as a mammographic sign of breast cancer but is highly predictive of breast cancer both at screening and diagnostic mammography [1]. Architectural distortion is a sign of invasive ductal and invasive lobular cancer and results from the fibrosis in a scirrhous carcinoma. Ductal carcinoma in situ most commonly manifests as indeterminate or malignant-appearing microcalcifications. However, a small percentage of DCIS can appear as areas of distortion, 2.1 % [4/190] in one series [12]. Architectural distortion in an area of DCIS is often attributed to associated sclerosing adenosis rather than due to the in situ cancer itself. In one series, 5 of 54 cases of DCIS [10.8 %] appeared as an area of architectural distortion. Histopathological correlation in this series showed that the AD in 4 of 5 cases correlated with sclerosis in the interstitium around DCIS, and DCIS in Cooper’s ligament accounted for the appearance of AD on the mammogram [13].

It is also known that in patients with architectural distortion on mammography, there is more likely to be positive margins than those with masses or calcifications [2]. Breast cancer presenting as AD is also reported to be significantly larger than that seen on mammography compared to other mammographic abnormalities. It is therefore recommended that in those patients with nonpalpable architectural distortions, a wider excision be undertaken to minimize the risk of having positive margins. Although most series of invasive breast cancers have found architectural distortion a less common mammographic presentation, architectural distortion has been reported to be more frequently seen in invasive lobular cancer. Architectural distortion was found to be the second most common appearance after a mass, in some studies ranging from 10 to 34 % of cases of invasive lobular cancer [14]. The differential diagnosis of an area of architectural distortion appears in Box 5.2. A finding of an architectural distortion on a mammogram except for those that can definitively be attributed to prior surgery, biopsy, or trauma is an indication for excisional biopsy in most instances. Known mimics of cancers that can appear as areas of architectural distortion include a radial scar and sclerosing adenosis.

Calcifications that are identified on a screening mammogram and that do not exhibit the established criteria of benign calcifications are recalled to undergo a diagnostic mammogram. Spot compression magnification views in the mediolateral and craniocaudal projections are routinely obtained. The rationale for obtaining magnification views is to study the morphology and the distribution pattern of the calcifications. Magnification mammography decreases noise and improves image sharpness allowing for optimal evaluation of the morphology and distribution of calcifications. A description of mammographically identified calcifications should include the morphologic features and the distribution of the calcifications. Macrocalcifications are typically larger than 2 mm and are associated with benign processes; microcalcifications are smaller than 0.5 mm and can be associated with ductal carcinoma in situ or invasive cancer [28]. In DCIS the tumor grows within the duct, distending it but remaining within the basement membrane.

Malignancies presenting as calcifications on mammography are most commonly associated with DCIS and have been reported in up to 68 % of cases of ductal carcinoma in situ [2]. About 29–47 % of breast cancers appear as microcalcifications without a mass [1]. About 24 % of the suspicious calcifications are associated with DCIS. Microcalcifications in DCIS are most commonly linear, linear branching, and fine pleomorphic, in a linear distribution. Other forms described in DCIS include the dot-dash pattern, consisting of round and needle-shaped calcifications.

The histological high-grade carcinoma or comedocarcinoma tends to be associated with linear, branching, and irregular calcifications that are in a linear or segmental distribution, formerly referred to as casting type of calcifications. These cancers may also be associated with pleomorphic or amorphous type of calcifications. In comedocarcinoma there is significant necrosis within the lumen of the duct that is involved with cancer. About 90 % of high-grade DCIS is associated with microcalcifications. The lower-grade or noncomedo DCIS is associated more often with clustered calcifications of amorphous or coarse heterogeneous morphology calcifications. Overall unlike the high-grade DCIS, the low-grade DCIS is less frequently associated with microcalcifications and reported in about 50 % of cases. Sometimes in DCIS one sees clustered fine pleomorphic or coarse heterogeneous calcifications, and these are often associated with necrotic tumors of the cribriform or micropapillary type [28]. The differential diagnosis for linear calcifications includes two important benign causes, secretory calcifications and vascular calcifications. Linear calcifications can be associated with benign secretory disease of the breast; these calcifications are often bilateral, regional, and seen in older women. When confined to a smaller region and unilateral, secretory calcifications are a challenge, these tend to be dense and have smooth margins [29]. Vascular calcifications when patchy and confined to one wall of a vessel may appear as a linear calcification. Magnification views help to identify the true nature of these benign vascular calcifications.

There have been reports attempting to correlate the appearance of microcalcifications with likelihood of invasive cancers [30]. In malignant calcifications without a focal mass, invasive foci are more likely when calcifications were larger than 11 mm and with linear calcifications than with granular calcifications [30]. Invasive cancers presenting as calcifications are often associated with high-grade DCIS and are also more likely to be Her2/Neu [human epidermal growth factor receptor 2]-negative cancers [2]. Invasive ductal cancers may also be associated with fine pleomorphic calcifications (Fig. 5.8). Invasive lobular cancer on the other hand is rarely associated with microcalcifications.

The morphologic types of calcifications that are suspicious for malignancy can be categorized as those with intermediate concern for cancer and those that have a higher probability of being associated with breast cancer [5] (Table 5.1).

Focal asymmetry is a localized area of increased density that is visible as a confined asymmetry with similar shape in two views, but does not fit the criteria of a mass and lacks defined borders. In majority of cases it represents an island of normal breast tissue especially when there is interspersed fat. Focal asymmetry that is associated with a palpable finding, architectural distortion, or microcalcifications is worrisome for malignancy [5, 31]. Breast asymmetry is generally a result of localized distribution of fibroglandular parenchyma and unlike a mass tends to have concave borders and is interspersed with fat and not dense centrally like one sees in a mass. To appreciate breast asymmetry views of each breast are inspected side by side as is standard practice of viewing mammograms. There are four types of breast asymmetry described [32]:

Sonography is an appropriate work-up for a focal asymmetry that is persistent mainly to exclude an underlying mass. In one series sonography had a negative predictive value for breast cancer of 89.4 % (7/9 cancers detected). One palpable focal asymmetry without a sonographic correlate proved to be an invasive ductal cancer as did one without a palpable correlate. A negative sonography should not preclude biopsy in those with a palpable focal asymmetry. However, the presence of localized hyperechoic tissue matching an area of focal asymmetry is suggestive of a benign process [37]. See Fig. 5.11a–d.

In summary, most cases of asymmetry are due to a summation artifact and appropriately categorized as benign with a recommendation for routine follow-up. Those that are determined not to be a summation artifact after a diagnostic work-up and if new or enlarging or palpable following either a negative ultrasound examination or an ultrasound finding of an indeterminate mass get a category 4 assessment with a recommendation for a biopsy. Uncomplicated focal asymmetry seen on a baseline screening mammogram or when there are no prior mammograms available for comparison need to be worked up with diagnostic mammography and if persistent assessed by sonography; if there is no benign finding accounting for the focal asymmetry, the finding is considered probably benign with a recommendation for a short interval follow-up in 6 months. Uncomplicated global asymmetry does not require a diagnostic work-up and is assigned a BI-RADS 2 category with a recommendation for routine screening. Uncomplicated developing asymmetry is always recalled and if determined not to be due to summation or a sonographic benign correlate is categorized as a BI-RADS 4, with a recommendation for a biopsy. Asymmetry, global asymmetry, or a focal asymmetry associated with a palpable finding, architectural distortion, or suspicious microcalcifications is always an indication for biopsy.