Radiologic and histologic presentation of male mammary myofibroblastoma

Abstract

Mammary myofibroblastoma is a rare mesenchymal neoplasm that typically presents in older men and women. Less commonly, these benign tumors may also occur in soft tissues located outside of the breast, in which case they are referred to as mammary-type myofibroblastomas. The histologic composition of this benign spindle cell tumor can be markedly varied. We present a case of a large mammary myofibroblastoma in a male patient and discuss the typical imaging and histologic makeup of these tumors.

Mammary myofibroblastomas are rare benign stromal cell tumors that can occur in both men and women. With the prevalence of screening mammography, these neoplasms are now being detected at smaller sizes. However, patients, especially men, can present with a palpable mass where screening mammography is not routinely performed. This case highlights the clinical presentation, imaging appearances, and pathologic features of this rare benign neoplasm.

CASE REPORT

A 57-year-old man presented with a right breast mass that had been slowly increasing in size over the past 5 years. He denied a personal or family history of cancer. The mass was firm, mobile, nontender, and involved the entire right breast. It measured approximately 10 cm in greatest diameter. There was no skin erythema, nipple retraction, or nipple discharge. No axillary or supraclavicular adenopathy was palpated. A mammogram disclosed an oval mass with circumscribed margins measuring up to 10 cm and occupying most of the right breast (Figure 1a, 1b). Ultrasound demonstrated an oval, solid mass with circumscribed margins measuring 10 cm. The echotexture of the mass was heterogeneous (Figure 1c). Internal vascularity was noted on color Doppler imaging, confirming the solid nature of the mass. A survey ultrasound of the axilla detected no abnormal axillary lymph nodes. Percutaneous biopsy under ultrasound guidance yielded four 14-gauge core specimens, which on histopathologic diagnosis revealed mammary myofibroblastoma.

Figure 1.

(a) Right cranial-caudal and (b) mediolateral-oblique mammographic views demonstrate a high-density oval mass with circumscribed margins occupying all four quadrants of the right breast. This mass corresponds with the palpable area of concern. (c) Gray-scale ultrasound image of the corresponding mass demonstrates a heterogeneous, oval solid mass with circumscribed margins.

The patient was subsequently referred to a breast surgeon for excision. Using a bat wing excision, the subcutaneous tissue was dissected using electrocautery. The mass was removed intact with blunt dissection. An intraoperative specimen radiograph confirmed excision of the mass and biopsy clip. The deep dermis and skin were subsequently closed. The excised mass measured 11.0 × 9.2 × 6.5 cm and weighed 279 g. On cut section, the mass was well circumscribed, tan-white to yellow-tan, firm, nodular, and homogenous, with no areas of hemorrhage, necrosis, overt calcium, or cystic degeneration (Figure 2a). The mass consisted of uniformly cellular, basal spindle cells arranged in short and long fascicles and an occasional storiform pattern, with interspersed thick and thin collagen fibers (Figure 2b). No area of necrosis or infiltration into the surrounding breast parenchyma was noted. The spindle cells showed a low nuclear to cytoplasmic ratio, moderate eosinophilic to amphophilic cytoplasm, and elongated nuclei with blunted ends (Figure 2c). Rare mitotic figures were noted.

Figure 2.

(a) Gross specimen of the mass following surgical excision. (b) Hematoxylin and eosin (H&E) stain, 4×, of the specimen demonstrates the uniformity of the basal spindle cells in short and long fascicles, typical of a myofibroblastoma. (c) H&E stain, 20×, of the specimen demonstrates a closer view of the spindle cells with the rare mitotic figures and low nuclear to cytoplasmic ratio.

Based on cytomorphology, immunohistochemical analysis excluded spindle cell metaplastic carcinoma and metastatic melanoma. The spindle cells were strongly and diffusely positive with CD34, smooth muscle actin, desmin, estrogen receptor, and progesterone receptor immunostains, compatible with the diagnosis of mammary myofibroblastoma. The tumor cells were negative for pan-cytokeratin AE1/AE3 and S100, excluding spindle cell metaplastic carcinoma and spindle cell melanoma, respectively.

DISCUSSION

First reported by Toker in 1981 (1) and first named by Wargotz in 1987 (2), mammary myofibroblastoma is a mesenchymal neoplasm derived from stromal fibroblasts. Although myofibroblastomas have been reported in extramammary locations, they are most commonly found within the breast parenchyma. These masses are termed myofibroblasts because they are considered to be fibroblastic cells that show smooth muscle differentiation since they express desmin and actin (smooth muscle markers). When in the breast, this benign lesion usually presents as a firm and mobile mass. Typically, it is unilateral, painless, and may steadily increase in size. It can reach large dimensions, as in this case, but usually ranges from 1 to 4 cm. The demographic distribution of myofibroblastoma of the breast occurs with equal prevalence, predominantly in older men and women with a median age of presentation of 55 years (3). Often, this mass will present a diagnostic dilemma both on imaging and clinically, as its features may overlap with those of other benign and sometimes malignant lesions.

The imaging features of mammary myofibroblastoma are nonspecific. Consequently, these lesions are hard to characterize as definitely benign or malignant, prompting the need for biopsy. With the widespread use of screening mammography, many lesions may be detected at small sizes (approximately 1 cm). The lesion typically appears as a well-circumscribed oval or round high-density mass on mammography. Architectural distortion and calcium are not typical features of this benign neoplasm (4). Sonographically, the mass usually presents as an oval, circumscribed hypoechoic solid mass. Its echogenicity, however, can be hyperechoic, and posterior acoustic shadowing may be present (4). On magnetic resonance imaging, these lesions typically enhance and can demonstrate internal septations on T2-weighted images (5). Myofibroblastomas are typically surgically excised with a good prognosis.