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Case Diagnosis and Discussion


Mammary Hamartoma (Fibroadenolipoma)


Mammary hamartomas are infrequently identified, benign tumors of the breast that contain glandular, fibrous, and adipose tissue. Hamartomas are frequently under-recognized due to non-specific histologic features that can be similar to other benign and malignant breast lesions including fibroadenoma and phyllodes tumor[1].

In contrast to fibroadenomas, in which terminal ductal lobular units are distorted secondary to intervening fibrosis, hamartomas have preservation of terminal ductal lobular unit architecture, with fibrosis limited mostly to the interlobular spaces, as in this case (Figure 1)[2].

Another distinguishing feature of hamartomas in comparison to fibroadenoma is the presence of intralesional adipose tissue. Fat is present in the vast majority of hamartomas, and can comprise a small proportion, or the majority of the mass, the latter of which are sometimes referred to as adenolipomas[1]. In this specimen, there are scattered adipocytes between ductal lobules, comprising a small proportion of the mass (Figure 3), with the majority of the lesion comprised of fibrous tissue. Less commonly, hamartomas can display myoid or chondromyxoid differentiation[3].

Although hamartomas themselves are benign, there have been case reports of breast carcinomas arising from these lesions, and thus should be treated with excision[4]. For this patient, the glands within the hamartoma displayed normal luminal cells without hyperplasia or dysplasia (Figure 2). In any case of an enlarging tumor with a significant fibrous stromal component, phyllodes tumor should be considered, however in this case, the lesion was well-circumscribed, and lacked the characteristic “leaf-like” architecture of phyllodes tumor[5], making that diagnosis less likely.


1. Amir, R.A. and S.S. Sheikh, Breast hamartoma: A report of 14 cases of an under-recognized and under-reported entity. Int J Surg Case Rep, 2016. 22: p. 1-4.

2. Daya, D., et al., Hamartoma of the breast, an underrecognized breast lesion. A clinicopathologic and radiographic study of 25 cases. Am J Clin Pathol, 1995. 103(6): p. 685-9.

3. Jones, M.W., H.J. Norris, and E.S. Wargotz, Hamartomas of the breast. Surg Gynecol Obstet, 1991. 173(1): p. 54-6.

4. Mester, J., et al., In situ and infiltrating ductal carcinoma arising in a breast hamartoma. AJR Am J Roentgenol, 2000. 175(1): p. 64-6.

5. Ben Hassouna, J., et al., Phyllodes tumors of the breast: a case series of 106 patients. Am J Surg, 2006. 192(2): p. 141-7.

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