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Fibroepithelial Tumors and Hamartomas
Introduction
Fibroepithelial lesions of the breast are biphasic neoplasms comprised of variable amounts of stroma and benign epithelial elements. This spectrum of entities includes fibroadenomas and phyllodes tumors. Hamartomas are composed of the lobular glands of normal breast tissue set within a circumscribed, often encapsulated-appearing, fibroadipose tissue mass. Given the resemblance of hamartomas to fibroepithelial lesions, they are discussed together in this chapter. Fibroepithelial lesions and hamartomas most commonly present as a palpable mass, arising in any location within the breast parenchyma or along the milk line. Hamartomas are benign tumors of the interlobular stroma, whereas fibroadenomas and phyllodes tumors originate from the specialized, intralobular stroma. Hamartomas and fibroadenomas demonstrate benign behavior, with rare local recurrences, likely representing continued local growth. Clinical outcome for phyllodes tumors depends on the characteristics of the stromal component and adequacy of excision. Rarely, hamartomas and fibroepithelial lesions may contain atypical hyperplasia or carcinoma in situ, or demonstrate involvement by a proximate invasive carcinoma.
Hamartoma
Clinical Features
Hamartomas most commonly present as a soft, often painless, palpable mass but may be detected by mammography in asymptomatic patients. Ultrasonography is the imaging modality of choice for evaluation of hamartomas, characteristically showing a circumscribed round to ovoid mass with heterogeneous intralesional echogenicity. Hamartomas can occur sporadically and in association with chromosome 12 abnormalities and Cowden syndrome. Patients with PTEN germline mutations are at an increased risk for breast, thyroid, gastrointestinal tract, central nervous system, and skin tumors.
Epidemiology
Hamartomas comprise 1% to 5% of benign breast masses, most commonly presenting in middle-aged women at a mean age of 45 years but may occur over a wide age range from the second to eighth decades.
Macroscopic Appearance
Hamartomas are well circumscribed, round, ovoid, or lobulated and can measure up to 20 cm. The cut surface is fatty and nearly indistinguishable from the adipose tissue in the surrounding mammary parenchyma.
Histopathology
Hamartomas consist of benign breast ducts and lobules, adipose tissue, and cytologically bland interlobular fibrous tissue of varying proportions contained within a thin pseudocapsule ( Fig. 22.1 ). The epithelium typically maintains the normal terminal duct–lobular unit architecture. Hamartomas in younger patients may also display fibrocystic changes including usual ductal hyperplasia, sclerosing adenosis, and apocrine cysts. The presence of pseudoangiomatous stromal hyperplasia (PASH) and prominent fibrocystic changes may mimic fibroadenomas; however, hamartomas lack the lobulated architecture created by the regular expansion of loose myxoid intralobular stroma that is seen in fibroadenomas. Benign mesenchymal elements including smooth muscle and cartilage derived from the nonspecialized mammary parenchyma may be present. When smooth muscle differentiation is prominent the lesion is termed a myoid hamartoma .
Treatment
Management options include observation, enucleation, and surgical excision. These lesions behave in a benign fashion, with surgical procedures performed for cosmesis and pain management.
Prognosis
Rare local recurrences likely represent continued growth of an incompletely removed lesion and should be managed conservatively.
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