Dermatofibrosarcoma Protuberans: A Second Primary Tumor Displaying Bednar and Fibrosarcomatous Subtypes

Authors


Dermatofibrosarcoma protuberans (DFSP) is a rare soft tissue tumor that is locally aggressive and has a high rate of local recurrence after inadequate surgical intervention.[1, 2] It accounts for 0.1% of all cancers and has an estimated incidence of 0.8–4.5 cases per million person-years.[1, 3] Complete surgical excision using wide local excision (WLE) or Mohs micrographic surgery (MMS) is the treatment of choice.[1, 2] We present a case of a second primary DFSP occurring in the same patient that exhibited the fibrosarcomatous and Bednar tumor subtypes.

Case Report

A 44-year-old man presented for evaluation and management of a fibrotic, ill-defined subcutaneous nodule on his left chest with a central scar. The lesion had been present for 5 years, and he stated that it had slowly progressed. Previous biopsy showed a deeply penetrating dermatofibroma that had been incompletely excised. His past medical history was significant for DFSP 3 years before on the right thigh that was confirmed using light microscopy and an immunohistochemical profile. There was no mention of a subtype in the pathologist's report. The DFSP was excised with wide margins. After excision, he had whole-body magnetic resonance imaging every 6 months with no abnormal findings.

Incisional biopsy of the left chest nodule showed a neoplasm composed of ovoid to short spindled cells arranged in varying patterns, including short fascicles, storiform pattern, and sheets (Figure 1). The neoplasm extended into and through the subcutaneous adipose tissue in a lace-like fashion and extended for great distances along fibrous septae within the subcutaneous adipose tissue. Neoplastic tissue was present at numerous inked lateral and deep margins. Immunohistochemical CD34 staining (Figure 2) showed a distinctive biphasic pattern with the less cellular areas showing strong, intense, and diffuse staining, whereas the more cellular areas showed weak and patchy staining; CD163 highlighted histiocytes and factor XIIIa highlighted scattered dendritic cells in the tissue. These features are that of a DFSP. One area of the biopsy (Figure 3) was remarkable in that this neoplasm showed much higher cellularity and focally showed a prominent herringbone pattern, suggesting the fibrosarcomatous subtype.

Figure 1.

Hematoxylin and eosin stain showing ovoid to short spindled cells in varying patterns (original magnification ×20).

Figure 2.

CD-34 stain showing biphasic pattern (original magnification ×20).

Figure 3.

Hematoxylin and eosin stain showing the prominent herringbone pattern of the fibrosarcomatous subtype (original magnification ×200).

The patient was referred for MMS and underwent excision of the left chest lesion using frozen-section histopathologic evaluation for marginal clearance. The first Mohs layer was carried to the pectoralis fascia with a 1-cm peripheral clinical margin and found to be positive along the deep margin. In addition to the unusual fibrosarcomatous changes seen on the initial incisional biopsy, the deeper Mohs sections showed spindled, storiform cells interspersed with pigmented cells, consistent with the pigmented variant of DFSP known as a Bednar tumor (Figure 4). An additional subcutaneous layer was carried through the deep pectoralis major muscle and found to be clear histopathologically.

Figure 4.

Mohs frozen section showing spindled cells interspersed with pigment cells, consistent with Bednar tumor subtype (original magnification ×40).

The surgical defect was repaired using a pectoralis muscle imbrication and complex layered primary closure using surgical steel staples given the incisional length and tension. The patient had an uneventful postoperative course, and there was no evidence of recurrence in the 2 years after the procedure.

Discussion

DFSP typically presents as an asymptomatic skin-colored to pink plaque or nodule.[1, 2] Lesions progress slowly over a period of months to years.[1] The trunk is the most commonly affected site, accounting for 50% of cases.[1-3] DFSP typically occurs between 30 and 50 years of age, but congenital and pediatric cases have been reported[1, 3, 4]; 0.5–5% of tumors metastasize, with the lungs being the most common site of metastasis.[1]

On hematoxylin and eosin staining, DFSP shows dermal spindle cells that infiltrate into the subcutaneous fat in a classic storiform or cartwheel pattern.[1, 2, 4] Cells show little pleomorphism and a low mitotic index.[1, 2] CD34 and factor XIIIa are helpful to differentiate DFSP from dermatofibroma. DFSP typically appears to be CD34 positive and factor XIIIa negative, whereas dermatofibroma shows the opposite pattern.[1]

There are several DFSP variants, including the Bednar tumor and tumors with fibrosarcomatous dedifferentiation. Bednar tumors account for 1% of all DFSP.[1] Histologically, the Bednar tumor appears as a spindle cell tumor in a storiform pattern with melanin-containing dendritic cells.[1] Another variant is the fibrosarcomatous DFSP (DFSP-FS). This variant is thought to behave more aggressively and accounts for 7–16% of DFSP.[1, 4]

Complete surgical excision using WLE or MMS is the treatment of choice.[1, 5] The National Comprehensive Cancer Network recommends a 2- to 4-cm margin for WLE.[5] Foroozan and colleagues conducted a comprehensive review of the published data comparing WLE and MMS recurrence rates. They found 23 nonrandomized trials (4 comparative, 19 noncomparative). They concluded that the recurrence rate for MMS was 1.1%, versus 6–32% for WLE. Although WLE and MSS are both acceptable options, MMS is the preferred treatment option for lesions occurring on sites where tissue conservation is of importance, such as the head and neck,[1] and many consider MMS to be the treatment of choice for all lesions given the lower recurrence rate.

Given the remote locations of our patient's tumors (right thigh and left chest wall) and normal whole-body MRI in the interim, a metastatic lesion is unlikely. We conducted an electronic literature search for cases of two primary DFSP lesions occurring in the same patient. We were able to find only one case report of a patient noting two separate DFSP lesions occurring in separate pregnancies.[4] The reason for the rarity of reported second primary tumors is unknown but could be because of the mathematical probability of a second rare acquired disease occurring in the same patient. Furthermore, this case demonstrates features of the Bednar and fibrosarcomatous subtypes, which is an uncommon occurrence that has not been reported in a second primary DFSP.

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