INTRODUCTION

Dermatofibrosarcoma protuberans is a rare slow- growing fibrohistiocytic, intermediate-to low-grade malignancy. It accounts for approximately 0.1% from all cancers and 1-6% of soft tissue sarcoma (1-3). It usually occurs in young to middle-aged individuals and commonly affects trunk, proximal extremities, head, and neck (1,4). Most cases present with slow- growing bluish or brownish erythematous skin nod- ules. It could also present as a keloid scar (1,5). DFSP typically arises in the dermis, has indolent growth but could be locally aggressive as it spreads into the sub- cutaneous tissue and muscles (1,2). It rarely has dis- tant metastasis with the lung the most common site of metastasis. Intra-abdominal metastasis is rare (1,2,4,5). Treatment for DFSP is either wide local excision or Mohs surgery. It frequently recurs locally in cases of incomplete excision with a recurrence rate of up to 53% being reported (5,6).

Clinical presentation

We report a 41-year-old female with a previous histo- ry of dermatofibrosarcoma protuberans of the left shoulder 1 year before the current presentation. Her initial presentation was a mass over the left shoulder progressively increasing in size over 4 months with core biopsy consistent with DFSP. There were no dis- tant metastases on imaging. She underwent wide local excision of the tumor and histopathology reported tumor margin of less than 3 cm. Adjuvant radiothera- py was planned but she defaulted due to logistic rea- sons. Her current presentation is an intestinal

obstruction for 3 days in December 2018. Exami- nation revealed intra-abdominal mass measuring 15 cm x 15 cm over the left flank. The prior surgi- cal wound over the left shoulder was well-healed with no evidence of local recurrence. Abdominal x -ray showed dilated proximal small bowel.

Contrast-enhanced CT thorax, abdomen, and pel- vis showed a well-defined intra-abdominal mass measuring 15x 17x 20 cm causing intestinal ob- struction and evidence of lung metastasis (Figure A and B). She subsequently underwent laparotomy and tumor debulking. Intraoperative findings showed a multilobulated soft tissue tumor measur- ing 20cm x 20cm along the mesenteric plane with extension into the retroperitoneum. Complete exci- sion of the tumor was achieved. The tumor dis- placed the descending colon and retroperitoneal structure medially and caused external compres- sion on the small bowel. The intestine and its asso- ciated vascular trunks were preserved.

Histopathological examination of the tumour showed a fairly circumscribed and unencapsulated tumour composed of fibroblastic spindle-shaped cells arranged in a herringbone pattern, with a mi- totic index of 6/10 HPF. Immunostaining was posi- tive for CD 34 (Figure E, F, and G). The histo- pathology assessment was consistent with meta- static high-grade fibrosarcoma.

Post-surgery she was started with intravenous chemotherapy ifosfamide and doxorubicin for 4 cycles. Her condition did not improve post chemo- therapy and she developed tumor recurrence.

DISCUSSION

Dermatofibrosarcoma protuberans (DFSP) is a mes- enchymal neoplasm that typically involves both der- mis and subcutaneous tissue (1,7). It commonly oc- curs in the trunk followed by the extremities, head, and neck (3,5). The lesion is usually painless, has in- dolent growth but is locally invasive with invasion into the underlying fascia, muscles, or bones (1,4,7). Even though this tumour is aggressive locally, distant metastasis is not common with less than 5% reported cases in the literature (6). It has hematogenous spread, typically to the lungs. Cases of metastases to the retro- peritoneum, mediastinum, bones, the kidney, brain, omentum, scalp, ovaries, liver, and heart have been reported (4,8).

It is difficult to diagnose DFSP since the early clinical symptoms are non-specific, it is slow growing and mimics another non-malignant tumour such as dermatofibroma. Dermatofibroma appears similar clinically and is distinguished from DFSP by the ab- sence of extension to deeper structure and the size of the lesion (3,5). The standard diagnosis of DFSP is by tissue biopsy with histopathological and immunohisto- chemical assessment. Imaging is for the assessment of extension to the deeper and surrounding structures as well as for operative planning. Computed tomography and MRI are both acceptable options, but MRI pro- vides a better assessment of the tissue infiltration and depth of involvement. It is also useful for preoperative and post-operative evaluation (5).

The histological features in DFSP are characterized by spindled cells arranged in a distinct herringbone or storiform pattern and immunohistochemical staining positive for CD-34 (1,2,4,7). There are several histo- logical variants of DFSP that have been described including myxoid, pigmented, atrophic, giant cell fi- broblastoma (GCF), and DFSP with fibrosarcomatous change (5). Dermatofibrosarcoma protuberans with fibrosarcomatous areas (DFSP-FS) is recognized as a high-grade type of variant, with higher rates of local recurrence and potential for distant metastasis. This case presentation is most consistent with the DFSP-FS subtype (2). The diagnosis of DFSP-FS is based on Enzinger and Weiss’s criteria. It includes the

71

presence of fibrosarcomatous changes of more than 5 mitoses/10 HPF, fascicular growth pattern, increased cellularity, and atypia in at least 5% of the tumor tissue (9).

The standard treatment for DFSP is wide local excision with a margin of more than 3 cm. The alternative approach includes Mohs micrographic surgery (MMS) which requires immediate micro- scopic examination of the margins in order to en- sure a tumor-free margin (1,3,5,7). The recurrence rate associated with MMS is less than 2% with no reports of distant metastasis (2,10).

MMS applies systematic horizontal sectioning compared to the traditional method which applies vertical sections which only assess limited tumor margin. In MMS, all sides of tumour are assessed using a frozen section which allows for a complete evaluation of tumour margins (11).

DFSP is a radiosensitive tumour and indication for radiotherapy includes the margin-positive tumour, unresectable tumour, or recurrent tumour (5). Ty- rosine kinase inhibitor such as Imatinib, Sunitinib, and Sorafenib has been shown to induce regression of DFSP and has been applied clinically in recur- rent, metastatic, or advanced diseases (5,7). The response rate of tyrosine kinase inhibitor in this clinical scenario of distant intra-abdominal metas- tasis is unknown as the efficacy of tyrosine kinase inhibitor in DFSP is only proven in the adjuvant setting after resection of primary high-risk tumors (12). Conventional chemotherapy has a limited role in the treatment of DFSP and is associated with poor response rates and clinical outcomes (5). Doxorubicin and ifosfamide for five or six cycles are the common regimes that are applicable in DFSP (5). In regards to this case, it is one of the rare cases of aggressive DFSP-FS that presents with intestinal obstruction due to intra-abdominal DFSP-FS metastasis. We, therefore, advocate a close follow-up protocol in all cases of DFSP which not only leads to a higher rate of compliance to adjuvant treatment but also provides a platform for early detection of possible tumor recurrence.