Approximately 85 percent of breast carcinomas arise from ductal structures, with the remaining 15 percent arising from lobular structures. Infiltrating ductal carcinoma accounts for the largest group of breast cancers, representing 65 to 80 percent of cases.10 The classic mammo-graphic presentation of infiltrating ductal carcinoma is a high-density mass with spiculated margins (Figure 3-3A). Sonographically, this lesion is typically seen as a shadowing, hypo-echoic mass with irregular margins (Figure 3-3B). The presentation of infiltrating ductal car
Figure 3-3. A, Classic mammographic appearance of infiltrating ductal carcinoma demonstrating irregular, spiculated margins. B, Sonographic visualization of the same infiltrating ductal carcinoma illustrating a hypoechogenic mass with irregular margins.
Figure 3-4. A, Mammographic spot view of a 0.8 cm infiltrating ductal carcinoma with microlobulated and partially ill-defined margins. B, Sonographic image of the same infiltrating ductal carcinoma demonstrating the marked irregularity of the tumor margins (arrows), despite the small size.
cinoma, however, can mimic a benign lesion with partially circumscribed margins (Figure 3-4).
Infiltrating lobular carcinoma is the second most common type of invasive breast cancer, representing approximately 15 percent of cases.10 It has a higher rate of multicentricity and bilaterality than infiltrating ductal carci-noma.11 Infiltrating lobular carcinoma is known for its insidious nature, delaying clinical and mammographic diagnosis. The subtle nature of infiltrating lobular carcinoma is thought to be due to its pattern of single-file cellular infiltration and lack of associated desmoplastic reac-tion.12 This tumor often presents as an evolving asymmetric density, or, less often, a spiculated mass on mammography (Figure 3-5 A).13,14 Despite its elusive appearance on mammography, infiltrating lobular carcinoma appears sono-graphically indistinguishable from infiltrating ductal carcinoma (Figure 3-5B).3
Medullary, colloid, and papillary carcinomas often present as partially circumscribed mammographic masses. Medullary carcinoma, accounting for approximately six percent of breast carcinomas, typically presents in patients < 50 years of age and can be mistaken for a fibroadenoma (Figure 3-6). The slow growing colloid carcinoma, also known as mucinous carcinoma, comprises only two percent of all breast cancers and is more common in older females (Figure 3-7). Papillary carcinoma represents less than one percent of all breast cancers and is associated with spontaneous serosanguinous nipple discharge. An
intracystic mass or intraductal lesion depicted by sonography raises concern for a papillary neoplasm (Figure 3-8).
Tubular carcinoma accounts for less than two percent of breast cancers. Due to its very slow growth, this tumor is typically small at the time of detection. Tubular carcinoma often presents as a small spiculated mass on mammog-
raphy, indistinguishable from infiltrating ductal carcinoma (Figure 3-9). Tubular carcinoma can be confused or associated with a radial scar (sclerosing papillomatosis), a benign entity (Figure 3-10).
Phyllodes tumor, once termed "cystosarcoma phyllodes," comprises less than one percent of breast tumors. Approximately ten percent of
phyllodes tumors are malignant. This tumor can present as a rapidly growing palpable mass. Breast imaging usually shows a large rounded or lobulated circumscribed mass. Cystic spaces can be seen by sonography (Figure 3-11).
Metastasis to the breast, although uncommon, can occur from a variety of primary malignancies, including melanoma, lymphoma, lung cancer, and contralateral breast carcinoma. Mammographically, the metastatic lesions tend to be round and lack spiculations (Figure 3-12).
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