Facial subcutaneous dermatofibrosarcoma protuberans treated with imatinib and monitored with magnetic resonance: a therapeutic alternative for unresectable cases

Subcutaneous dermatofibrosarcoma protuberans (SC-DFSP) was recently characterized as an uncommon subtype of DFSP.¹ It was initially described by Diaz-Cascajo in 1998 as ‘deep DFSP’.² It appears as a poorly circumscribed tumor or nodule that involves subcutaneous tissue but lacks the visible nodular surface of classic-DFSP. SC-DFSP occurs more commonly on the head and neck and may extend significantly beyond the palpable clinical lesion. Compared to classic DFSP, SC-DFSP requires a greater number of Mohs stages to clear margins and is more likely to extend to deeper structures such as the muscle or periosteum. Therefore, there is a high-risk for large surgical defects, necessity for complex reconstruction, and cosmetic deformity or functional impairment in the head and neck region.¹ Oral tyrosine kinase inhibitor imatinib has been successfully used to treat unresectable or metastatic classic-DFSP and DFSP with fibrosarcomatous change.³ We present a case of locally advanced SC-DFSP on the head and neck that demonstrated clinical and radiographical response to therapy with imatinib.

Case report:

A 33-year-old female was referred for evaluation of an indurated lesion on the left face. On physical exam, there was an ill-defined 7.0 × 2.0 cm subcutaneous plaque extending from the left medial canthus to the medial cheek with no overlying epidermal change (Figure 1A). Biopsy demonstrated a proliferation of atypical spindle cells invading the deep dermis and the subcutaneous tissue without involvement of the epidermis and papillary dermis (Figure 2A). Immunohistochemical examination was strongly positive for CD34 at the subcutaneous level only, confirming the diagnosis of SC-DFSP (Figure 2B). FISH analysis detected PDGFB-COL1A1 gene rearrangement in 74% of cells. To further evaluate tumor extension, a baseline contrast enhanced magnetic resonance (MR) was performed. Imaging showed a low-signal infiltrative tumor in the subcutaneous soft tissue of the left cheek (Figure 1B).

Figure 1:

Subcutaneous dermatofibrosarcoma protuberans. A. Clinical features. The dashed line represents the extension of the tumor by palpation. This patient was not a surgical candidate and therefore imatinib was started. B. Baseline axial T1-weighted pre-contrast magnetic resonance image (MR) showing a low-signal infiltrative tumor in the subcutaneous soft tissues of the left cheek (arrow). C. Clinical features after 48 months of imatinib. The dashed line represents the reduction on the induration by palpation. D. 48-month follow-up axial T2-weighted pre-contrast MR showing a marked reduction on the low-signal tumor on the soft tissues of the left cheek (arrow).

Figure 2:

Subcutaneous dermatofibrosarcoma protuberans. A. Histopathologic examination showed a proliferation of atypical spindle cells at the deep dermis and subcutaneous tissue with storiform pattern (black arrows), sparing the epidermis and papillary dermis (H&E, 4X). B. Immunohistochemical examination was strongly positive for CD34 in spindle cells (black arrows) at the subcutaneous level (20X).

As surgical resection was likely to cause significant cosmetic and functional impairment, without guarantee of achieving tumor-free margins, the decision was made to initiate imatinib 400 mg daily. At 6 months, clinical evaluation demonstrated reduction of width and length of tumor by palpation. MR showed decrease in the tumor area. After 48 months of continuous treatment with imatinib, there was complete radiographic response and partial clinical response (Figure 1C–D). Side effects were mild and included occasional muscle cramps. No laboratory abnormalities were noted. After thorough multidisciplinary discussion, withdrawal of imatinib is being considered due to stable disease. In the absence of set guidelines, patient will be followed clinically using deep palpation every 6 months and with MRI every 6–12 months. If any regrowth is noted, imatinib therapy will be resumed.

Complete surgical excision with negative margins remains the cornerstone of treatment for DFSP.^4,5 However, in certain cases, surgical resection with curative intent can result in significant cosmetic and functional disfiguration. This is especially relevant for SC-DFSP cases, where the most common location is the head and neck and larger defects have been described due to frequent subclinical extension.¹ There is a growing role for imatinib³ and other targeted therapies as neoadjuvant or primary treatment when surgery is not feasible.⁶ NCCN guidelines state that imatinib could be considered in cases where disease is unresectable or unacceptable functional or cosmetic outcomes will occur with resection. This case highlights (1) the importance of recognizing SC-DFSP as a unique DFSP subtype, (2) the use of imatinib for unresectable SC-DFSP, (3) as well as the use of MR to monitor imatinib response and for follow-up after imatinib withdrawal.