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Breast masses occur frequently, as evidenced by more than 1.3 million excisional biopsies performed on American women yearly.1,2 Approximately 80% of these procedures are for benign lesions, most commonly fibroadenomas.1-4 Although it has been repeatedly stated that one-third to one-half of fibroadenomas will regress within 5 years of diagnosis, the data on the natural history of fibroadenomas varies.5-8 Fibroadenomas may occur at any age, but are most likely to occur in the second and third decades of life and are the most common breast masses in women under 30 years of age.2,9-11 Up to 10% of women will develop a fibroadenoma during their lifetime, and the majority will choose to undergo a procedure to remove the mass.2,4 Fibroadenomas account for 30% to 75% of all breast biopsies, more than 500,000 annually, and 75% of breast biopsies in women younger than 20 years.3,9,10

Fibroadenomas have typical characteristics on physical exam, mammography, and ultrasound.9 On physical exam, a fibroadenoma is a painless, spherical, smooth, and mobile mass (historically termed a "breast mouse" by European surgeons) with highly circumscribed margins, typically 1 to 3 cm in diameter.2,3,9 Ultrasound characteristics are typical of a benign mass and include a smooth, well-defined lesion that is iso- or mildly hypoechoic. It may be surrounded by a thin, echogenic pseudocapsule.12,13 On mammography, fibroadenomas are again seen as smooth round or oval masses that may contain course calcifications; multiple lesions may be noted.12,13 Fibroadenomas may be multiple in up to 15% to 20% of patients, especially dark-skinned individuals.2,10,12 The differential diagnosis for these lesions includes fast-growing juvenile fibroadenoma, phyllodes tumor, and colloid and medullary carcinomas.2 Most lesions require biopsy at some point. Others may be monitored without biopsy if they meet strict criteria, such as those described by Stavros and colleagues.14 Image-guided large-core needle biopsy is the method of choice, as the sample provides better differentiation of benign from malignant masses and fibroadenoma from phyllodes tumor.2

Acceptable management includes observation, excisional biopsy, and newer, minimally invasive alternatives. Adolescents may be safely observed for a period of time after physical exam reveals an apparently benign mass. Older women and those with persisting or enlarging masses should have histologic confirmation.3 Although a period of observation is acceptable for teenage patients, there are several valid reasons to support treating some benign lesions more aggressively. Large lesions may become symptomatic, causing feelings of heaviness, asymmetry, pain, or discomfort.9 Infrequently, benign masses may increase in size during pregnancy or during use of hormonal contraception or other types of hormonal therapy.10 Emotional distress created by the frequent follow-up required when patients attempt nonoperative therapy causes many to choose alternative approaches.1,3,9 In addition, benign masses may impair physical examination and mammographic evaluation ...

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