Dermatofibrosarcoma Protuberans of the Breast

Dermatofibrosarcoma protuberans (DFSP) is a rare, low-grade, fibroblastic mesenchymal tumor originating from the dermis. It most commonly affects the trunk, followed by the proximal extremities (1). Involvement of the breast is uncommon, with an estimated incidence of 0.8–4.5% among DFSP cases, and an overall DFSP incidence of only 4.2–4.5 per million population (1-3). Surgical excision with 2-3 cm margin is the gold standard treatment (1, 2). Selected cases are subjected to radiotherapy or systemic therapy with Imatinib (2).

Due to its rare presentation, breast DFSPs are often misdiagnosed during clinical examination, commonly mistaken for dermatofibroma, hemangioma or fibroepithelial lesions, as clinicians are often not familiar with its occurrence in the breast (1).

Here, we report a case involving a 42-year-old woman with DFSP of the left breast, which was initially diagnosed as a benign phyllodes tumor based on core needle biopsy. However, the final histopathological evaluation of the wide local excision specimen diagnosed DFSP of the breast.

A 42-year-old woman presented with a discolored protruding lesion on the skin of the left breast which was insidious in onset and gradually progressive over the course of two years from approximately 2x1 cm to around  4x3 cm at presentation. The lesion was painless and non-itchy. She did not have any contributory family history. On clinical examination, a lobulated, exophytic, keloid-like lesion with pink to whitish discoloration was noted on the left breast, located just above the inframammary fold, extending from the 6 to 5 o’clock position. The lesion was well-defined, measured 4.2×3.0 cm, and was fixed to the overlying skin but free from the underlying breast tissue (Figure 1a). The right breast, the remaining left breast and bilateral axillae were unremarkable.

A mammogram with ultrasound correlation was performed. Mammogram (Figure 1b) demonstrated two high-density, lobulated lesions with well-circumscribed margins in the lower outer quadrant of the breast,12 cm away from the nipple measuring 2.6x2.1 cm and 2x1.9 cm respectively. No intramammary lesion or microcalcification were observed. Ultrasound correlation revealed a few well defined, oval shaped, solid hypoechoic lesions, the largest measuring 3x1.3 cm located at 5 o’clock position in the left inframammary fold, about 10 cm away from the nipple/areolar complex. The lesion exhibited cleft-like cystic spaces with posterior acoustic enhancement and significant internal vascularity on color Doppler. Axillae were normal. The findings were suggestive of phyllodes tumor. For histopathological confirmation, a core needle biopsy was done which showed a mesenchymal tumor, favoring benign phyllodes. It had ovoid to spindled shaped cells with no epithelial component. So, as this was a breast lesion with such morphology, phyllodes is the usual diagnosis (Figure 2).

Hence, no immunohistochemistry (IHC) was planned initially. The patient subsequently underwent wide local excision with 2 cm margin.

The perioperative period was uneventful. On histology, the resected specimen showed dermal-based spindle cell tumor with infiltration into the subcutaneous fat, sparing the underlying breast parenchyma. This tumor was composed of uniform, bland, spindle cells arranged in a storiform pattern with areas of whorled fascicles and characteristic entrapment of adnexal structures. No significant mitosis, nuclear atypia or necrosis were seen. On IHC these cells were diffusely positive for CD34 (Figure 3a, b). Features were consistent with DFSP. For confirmation, fluorescence in situ hybridization was done on the paraffin embedded tissue block, which showed PDGFB gene rearrangement (Figure 3c).

It is important to note that diagnosing DFSP with small core biopsy samples can be challenging, particularly in unusual anatomical locations such as the breast. In such limited samples where the representation of tumor is not adequate, the potential misdiagnosis with more common entities like benign phyllodes, solitary fibrous tumor, fibromatosis and cellular fibrous histocytoma is common. Given these challenges, a carefully selected IHC panel including CD34, STAT6, Beta catenin, S100 and Ki-67 is essential to distinguish DFSP from its closest morphological mimics in small biopsy samples. Informed consent was taken from patient.

Follow-up

The patient was planned for close follow-up post surgery. Clinical examination at three months of follow-up showed no evidence of recurrence and the surgical scar was healthy. A follow-up mammogram performed subsequently (post 3-months) showed no residual lesion or new abnormalities, indicating a favorable postoperative course.