Desmoid-Type Fibromatosis of the Male Breast: A Rare Case Report with Diagnostic Challenges and Histopathological Confirmation
Dr. Sakina Abidi, Dr. Azhar Uddin, Dr. Rimsha Tayyab, Dr. Javeria Parwez
*Correspondence to: Dr. Sakina Abidi.
Copyright.
© 2026 Dr. Sakina Abidi, This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Received: 13 September 2026
Published: 01 October 2026
DOI: https://doi.org/10.5281/zenodo.23076678
Abstract
Background: Desmoid-type fibromatosis (DTF) is the benign breast neoplasm that arise from fibroblasts and myofibroblasts and possess a high propensity for local recurrence even with adequate surgical resection (2). It accounts for less than 0.2% of all breast tumors and occurs predominantly in women(1). DTF involving the male breast is rare(5). Amongst the reported cases, women are diagnosed twice as often compared to men, which raises the question of hormonal influence(4). On physical examination and imaging,it can mimic malignancy (3). making histopathological and immunohistochemical evaluation essential for diagnosis.
Case Presentation: A 60-year-old man presented with a progressively enlarging right breast lump. Clinical examination revealed a firm, mobile mass measuring approximately 4 × 4 cm in the periareolar region without skin changes or nipple discharge. Ultrasonography demonstrated a heterogeneous hypoechoic lesion suspicious for a solid breast mass. A previous biopsy suggested benign breast tissue with focal chronic inflammation and fat necrosis. Because of persistent clinical suspicion, the patient underwent surgical excision of the lesion. Gross examination demonstrated an ill-defined gray-white firm lesion measuring 4.5 × 3 cm. Histopathological examination showed a spindle-cell proliferation arranged in fascicles within a collagenous stroma without significant atypia, necrosis, or increased mitotic activity. Immunohistochemistry revealed diffuse nuclear β-catenin positivity, focal smooth muscle actin positivity, and negativity for cytokeratin AE1/AE3, CAM5.2, CD34, S100, and desmin, confirming desmoid-type fibromatosis.
Conclusion: Desmoid-type fibromatosis should be considered in the differential diagnosis of a male breast mass. Histopathological examination supplemented by β-catenin immunohistochemistry is crucial for accurate diagnosis. Complete surgical excision remains an important treatment option, although careful long-term follow-up is recommended because of the risk of local recurrence.
Keywords: Male breast, Desmoid-type fibromatosis, Breast fibromatosis, β-catenin, Case report, Spindle cell lesion.
Introduction
Fibromatosis, or desmoid tumor of the breast, represents proliferation of myofibroblasts and fibroblasts that can be either a local indolent disease or a local infiltrative lesion(3). It is a locally aggressive lesion which exhibits a high incidence of local recurrence following incomplete excision(6) Breast involvement is particularly uncommon, accounting for less than 0.2% of all breast tumors(1).
Whilst the definite etiology of breast fibromatosis is unclear, it may present itself following surgical trauma or silicone implant(2).Some cases are reported showing the association with adenomatous polyposis (7)Most reported cases occur in women, whereas occurrence in the male breast is exceedingly rare(1,5).It shares the same clinical and radiological features of breast carcinoma(8),establishing the diagnosis may be challenging.One of the female patient was initially interpreted as a case of multicentric breast carcinoma (8).
Histologically, desmoid-type fibromatosis consists of bland spindle cells embedded in collagenous stroma with infiltrative margins(9). Intranuclear β-catenin staining is particularly useful for differentiating desmoid-type fibromatosis from other spindle-cell lesions of the breast(10)
We report a rare case of desmoid-type fibromatosis of the male breast in a 60-year-old patient, highlighting the diagnostic challenges, histopathological findings, immunohistochemical profile, and surgical management.
Case Presentation
A 60-year-old married male with no known comorbidities presented with a right-sided breast lump. Clinical examination demonstrated a firm, mobile swelling measuring approximately 4 × 4 cm located around the 10 o'clock position of the right nipple–areolar complex. There was no nipple discharge, overlying skin ulceration, or skin discoloration. Examination of the left breast was unremarkable.
Routine laboratory investigations, including complete blood count, renal function tests, serum electrolytes, hepatitis B surface antigen, and anti-hepatitis C virus antibodies, were within normal limits.
Preoperative ultrasonography demonstrated a solid heterogeneous hypoechoic lesion within the right breast. An earlier biopsy had reported benign breast tissue with focal chronic inflammation and fat necrosis, which was discordant with the persistent clinical findings.
The patient underwent surgical excision of the breast lump under general anesthesia. Intraoperatively, an ill-defined firm whitish lesion measuring approximately 6 × 4 cm was identified extending from the 9 o'clock to the 12 o'clock position. The lesion was gritty in consistency, poorly encapsulated, and densely adherent to the surrounding breast parenchyma. Complete excision of the lesion was performed.
The postoperative course was uneventful. The patient received appropriate analgesia and antibiotic therapy, resumed oral intake, remained hemodynamically stable, and was discharged in satisfactory condition.
Gross pathological examination revealed an irregular fibrofatty specimen measuring 4.8 × 3.5 × 2.5 cm. Cut section demonstrated an ill-circumscribed gray-white firm lesion measuring 4.5 × 3 cm with close and involved surgical margins.
Microscopically, the lesion consisted of bland elongated spindle cells arranged in vague fascicles within a collagenous stroma. Fig 1.0. The cells exhibited pale cytoplasm, elongated nuclei with inconspicuous nucleoli, and lacked significant cytological atypia, necrosis, or increased mitotic activity. Fig 2.0. Focal loose tissue culture-like areas with microhemorrhage were identified. Fig 3.0
Immunohistochemical analysis demonstrated diffuse nuclear positivity for β-catenin and focal positivity for smooth muscle actin. Cytokeratin AE1/AE3, CAM5.2, CD34, S100, and desmin were negative. These findings supported the diagnosis of desmoid-type fibromatosis. Although nodular fasciitis was considered in the differential diagnosis, the diffuse nuclear β-catenin staining favored desmoid-type fibromatosis.
Discussion
Desmoid-type fibromatosis (DTF) is a rare, benign,locally aggressive neoplasm arising from musculoaponeurotic structures.(10).Despite its benign histological appearance and lack of metastatic potential, it is characterized by infiltrative local growth and a significant risk of local recurrence(6).Desmoid tumors account for 0.2% of all breast tumors, and the disease predominantly affects women(1).A 2024 Frontiers in Oncology case report states that the occurrence of breast desmoid-type fibromatosis in males is “exceedingly rare” and reports that, according to the literature reviewed by the authors, only eight cases of male breast fibromatosis had been reported before their publication(11)hence every case report is significant to understand the diagnostic challenges and management approach of desmoid fibromatosis in male patients.
The clinical presentation of breast fibromatosis is often nonspecific. In a 25 years of observational study by Neuman et al breast desmoids presented as palpable masses suspicious for carcinoma clinically and radiographically(12).Tethering of the Cooper’s ligaments and involvement of the pectoralis muscle have been observed, indicating the locally aggressive nature of fibromatosis and accounting for the skin dimpling and nipple retraction(13). A case report by Schwarz et al, MRI findings of fibromatosis,in that case, mimiced breast carcinoma in its morphologic and pharmacokinetic features of enhancement.(14).Our patient presented with a firm mobile right breast lump without overlying skin changes or nipple discharge. Although these findings were not clinically suggestive of breast carcinoma but needed a further work up for getting managed.
Due to its rarity and histologic resemblance to other myofibroblastic lesions, desmoid tumors are initially misdiagnosed in approximately 30–40% of cases(15).In the breast ultrasound,it is demonstrated as an ill-defined hypoechoic masses with irregular margins and posterior shadowing(13).Other sonographi features include linear extension of lesions along the fascial plane,referred to as the fascial tail sign,and finger-like extension of lesions into the muscle,known as the staghorn sign(16).In mammography, the tumor can be identified only in one-third of the cases(13). In our case, ultrasonography demonstrated a heterogeneous hypoechoic lesion that did not help to support a definitive diagnosis, pointing towards the non specificity of imaging for such cases
A particularly noteworthy aspect of our case was the discordance between the initial pathological diagnosis and the final excision specimen. The previous biopsy demonstrated benign breast tissue with chronic inflammation and fat necrosis, whereas examination of the excised specimen established the diagnosis of desmoid-type fibromatosis. Sampling error and the infiltrative architecture of fibromatosis may contribute to false-negative or inconclusive biopsy results. Therefore, persistent clinical suspicion despite benign biopsy findings should prompt repeat tissue sampling or complete excision to establish an accurate diagnosis.
Histopathological examination remains the cornerstone of diagnosis. Microscopically, fibromatosis shows bland spindle cells aligned parallel to one another and arranged in long, sweeping fascicles in a fibrous stroma with variable collagen deposition(17).Its distinction from fibrosarcoma, with the absence of nuclear pleomorphism, high mitotic index, abnormal mitotic figures, extreme cellularity, necrosis and vascular invasion generally serve to distinguish fibromatosis from fibrosarcoma(18) Similar histomorphological features were observed in our patient, with bland spindle cells arranged in vague fascicles within a collagenous background without increased mitotic activity or significant atypia.
Immunohistochemistry (IHC) is a crucial step, particularly intranuclear β-catenin immunostaining for which approximately 80% of DF cases are positive(19).Nuclear accumulation of β-catenin resulting from CTNNB1 mutations is considered one of the most characteristic features of desmoid-type fibromatosis and strongly supports the diagnosis(19). In the present case, diffuse nuclear β-catenin positivity together with negativity for cytokeratin AE1/AE3, CAM5.2, CD34, S100, and desmin, and focal positivity for smooth muscle actin, was consistent with the immunophenotype described in previous reports. Although nodular fasciitis was considered in the differential diagnosis, the diffuse nuclear β-catenin staining favored desmoid-type fibromatosis.
Reference