A 33-year-old man reported to the primary care physician because of a palpable tumor in his left breast. Fine-needle aspiration biopsy showed no evidence of malignancy. One year later, the patient reported a 3-month period of rapid tumor growth. Physical examination revealed a protruding firm nontender movable mass measuring 5 × 7 cm, free from the skin surface and underlying tissue, with no nipple discharge. Ultrasound examination showed a solid tumor measuring 32 × 20 mm at the 3 o’clock position, suspected to be breast carcinoma. Right breast, axillary, cervical, supra-, and infraclavicular fossae were free from pathology. Repeated fine-needle aspiration biopsy revealed a benign lesion. Due to the discrepancy between clinical and pathological findings, an excisional biopsy was performed. The excised tumor measured 7 cm, the cut surface was smooth and glistening with a gray color, with focal gelatinous appearance (Figure 1A). The lesion was relatively well circumscribed but not encapsulated. Microscopical evaluation revealed a spindle-cell lesion, characterized by fibrous areas with increased cellularity alternating with less cellular myxoid ones (Figure 1B). Cells were arranged in a plexiform and whorled pattern (Figure 1C) with mild atypia. The tumor showed no nuclear pleomorphism, high cellularity, nor necrosis, and there were no mitoses (Figure 1D). Immunohistochemical staining was positive for vimentin and focally for smooth muscle actin (Figure 1E and 1F) and CD99, and negative for epithelial membrane antigen, Bcl-2, S100, and CD34. Ki-67 staining showed typical low proliferation index (Figure 1G). Low-grade fibromyxoid sarcoma (LGFMS) with positive excision margins (R1) was diagnosed. The patient was then referred for mastectomy with partial resection of the pectoralis major. The postoperative histopathological report described a neoplastic infiltration of gray-creamy color, growing in a diffuse pattern, including almost the entire mammary gland and reaching the pectoralis major (Figure 1H). Microscopic evaluation confirmed multiple, diffuse foci of LGFMS, reaching the pectoralis major without infiltrating it. Adjuvant radiation therapy (50 Gy in 25 fractions and a boost to the primary site: 16 Gy in 8 fractions) was administered. Follow-up data covering 6 years revealed no evidence of local recurrence or systemic dissemination.

Figure 1. Macroscopic and microscopic images of breast sarcoma in a man: A – gross image demonstrating the intermixed fibrous and myxoid components. The cut section revealed a lesion with tan-gray color and glistening appearance. B – tumor histology showing an admixture of alternating myxoid and fibrous areas (hematoxylin and eosin staining, magnification ×40). Macroscopic and microscopic images of breast sarcoma in a man: C – characteristic features including fibrous and myxoid areas, zones with increased cellularity around vessels, and areas with swirling whorled growth pattern (hematoxylin and eosin staining, magnification ×100); D – characteristic features: myxoid areas with regular, bland-appearing cells with minimal nuclear pleomorphism, low to moderate cellularity and typical curvilinear vessels (hematoxylin and eosin staining, magnification ×100); E – vimentin staining showing diffuse and strong reaction (immunohistochemical staining, magnification ×100); F – immunoreactivity for smooth muscle actin showing focal and weak reaction within tumor cells and strong reaction within the vessel wall (immunohistochemical staining, magnification ×100); G – Ki67 staining showing typical low proliferation index (immunohistochemical staining, magnification ×200); H – gross image of the breast and pectoralis major specimen (155 × 12 × 50 mm) showing a neoplastic infiltration of gray-creamy color with a diffuse pattern, involving almost the entire mammary gland and reaching the pectoralis major (view from the side of skin and subcutaneous tissue)

Breast tumors in men are rare, but often pose a challenging diagnostic problem. Malignant lesions in the male breast are extremely rare, while benign gynecomastia, steatomastia, and lipoma are the most common pathologies. Malignant tumors may include not only carcinomas but also sarcomas presenting with rapid growth, infiltration of surrounding tissues, and distant metastases. Breast sarcomas may develop secondary to radiotherapy or lymphoedema (angiosarcoma in Stewart-Treves syndrome after mastectomy) and as a malignant conversion of phyllodes tumor (cystosarcoma phyllodes comprise 10%–30% of all cases). Primary breast sarcomas occur almost exclusively in female patients and constitute less than 1% of all breast malignancies in both sexes. In males, primary leiomyosarcoma, myxofibrosarcoma, fibrosarcoma, primary angiosarcoma, and undifferentiated pleomorphic sarcoma have been reported.1-4 Similarly to other locations of soft tissue sarcomas, the recommended diagnostic approach includes magnetic resonance imaging with core needle biopsy.

Low-grade fibromyxoid sarcoma was firstly recognized by Evans in 1987 as a rare soft-tissue tumor with a high metastatic potential, despite a benign histological appearance. It occurs more frequently in young adults, slightly more often in men, presenting as a slowly growing painless mass usually in a subfascial location. To the best of our knowledge, this is the second reported case of LGFMS of the breast to date, following Zhang et al5 in 2018, and the first such case in a man. The diagnostic path presented here was suboptimal and does not reflect current standards. We advise physicians to always check recommendations and apply them in everyday practice.