The World Health Organization defined desmoid fibromatosis (DF) as a clonal fibroblastic proliferation derived from deep soft tissue capable of local infiltration [1]. DF is a rare disease that specifically affects the breast. DF accounts for only 0.2% of all breast neoplasms, and its etiology has not been established [2]. Through imaging studies, DF has been revealed to mimic carcinoma in appearance [3,4]. Owing to its rarity and mimicry of carcinoma, the diagnosis and optimal treatment of DF are challenging tasks [5]. Histopathological analysis, which reveals the proliferation of spindle cells in collagen deposits, is paramount for DF diagnosis [6,7]. Herein, we describe an uncommon DF at our institution and review the literature relative to our case.

Most DF cases manifest in the abdomen; however, extra-abdominal desmoid tumors account for approximately 4% of all desmoid tumors [1]. DF in the breast is rare, accounting for 0.2% of all breast neoplasms. The etiology of this condition has not been clarified. Hormonal and genetic factors are reportedly associated with DF genesis [8-10]. Trauma and surgical procedures, including augmentation with silicone implants, have also been reported to affect DF [10]. Bouab et al. [11] described a similar case of DF after breast reduction surgery. In the present case, the patient diagnosed with infiltrating ductal carcinoma underwent a mastectomy, axillary lymph node dissection of the right breast, and contralateral breast reduction. One year after surgery, the 2 cm nodules found in the left breast were confirmed to be DF. Ebrahim et al. [12] reported the patient demographics and clinical presentations of six fibromatosis cases of the breast over 10 years. One of the patients had a history of breast surgery. Previously, Hammood et al. [9] reported a case of DF in the breast and mentioned no identified risk factors except for oral contraceptive use. Similarly, no correlation was found with factors besides oral contraceptive use in the present case. With regard to hormonal factors, previous reports and the present case suggest that oral contraceptive use could be a risk factor.

DF in the breast appears similar to carcinoma on physical examination and imaging studies, making it challenging for clinicians to differentiate DF from malignancy [3]. Lorenzen et al. [4] reported 15 cases over a period of 10 years that were identified through a digital archive search. The clinical presentation and imaging findings were not specific to DF. Most patients had a palpable mass, and some had skin retractions. Some studies have suggested that preoperative magnetic resonance imaging could be helpful in assessing the total extent and chest wall invasion, but not differential diagnosis [12,13].

DF is diagnosed via core needle biopsy [7]. This diagnosis can be difficult because spindle cells can indicate various diseases, including nodular fasciitis, phyllodes tumor, and fibrosarcoma. A diagnostic excisional biopsy provides a greater chance of a confirmatory diagnosis. Microscopic examination revealed spindle cell proliferation and collagen deposition. The mitotic rate is low. The margin is infiltrative, extending into the surrounding tissues [12]. Additional information from immunohistochemistry, such as the expression of smooth muscle actin without the expression of cytokeratin, CD34, or S-100, plays an adjunctive role in the diagnosis.

No consensus has been reached regarding the treatment of DF of the breast. In the past, wide excision was performed for most cases of desmoid tumors. According to the European Consensus, it is not clear whether en bloc surgery should be the method of choice, as a progression-free disease course and spontaneous regression are documented in up to 88% of cases. No significant benefit was observed in active treatments, such as antihormone therapy, chemotherapy, and radiation therapy, compared to patients being observed [6]. Owing to the rarity of cases in the breast, insufficient information is available to compare such cases. A large prospective nationwide study on desmoid tumors revealed primary location as a prognostic factor for event-free survival (EFS) [1]. In this study, DFs were categorized as having unfavorable (such as the chest wall, head and neck, and upper limbs) or favorable locations (such as the abdominal wall, intra-abdominal, breast, digestive viscera, or lower limb). In cases with unfavorable locations, the 2-year EFS was 51.8% with the wait-and-see approach compared to 25.4% with surgery. However, surgery and active surveillance resulted in similar oncological outcomes in patients with favorable tumor locations (EFS: 62.8 vs. 69.6%). DF tends to recur frequently in up to 27% of cases. Two-year EFS was 32% after open biopsy compared to 57% after a core needle biopsy, suggesting that a proliferative wound healing process could be associated with recurrence. However, negative margins cannot exclude the possibility of recurrence.

As only few case reports are available on this disease entity, DF remains poorly understood. Further experience with more cases will help to better understand DF and develop a multidisciplinary approach to its clinical management.