MOHS MICROGRAPHIC SURGERY FOR THE TREATMENT OF DERMATOFIBROSARCOMA PROTUBERANS - RESULTS OF A MULTIINSTITUTIONAL SERIES WITH AN ANALYSIS OFTHE EXTENT OF MICROSCOPIC SPREAD

Background: Dermatofibrosarcoma protuberans (DFSP) is an uncommon soft -tissue tumor of the skin; its microscopic extent of invasion beyond t he grossly visible tumor is frequently difficult to appreciate. Althou gh wide local excision has been the standard treatment of DFSP, recurr ence rates range from 11% to 53%. Because Mohs micrographic surgery al lows the extent of excision to be tailored to the microscopic extent o f tumor, we evaluated this technique for the treatment of primary and recurrent DFSP. Objective: Our purpose was to determine the local recu rrence rate and microscopic extent of spread of primary and recurrent DFSP after treatment with Mohs micrographic surgery. Methods: The reco rds of 58 patients with primary and recurrent DFSP treated with Mohs m icrographic surgery at three institutions were reviewed and the macros copic and microscopic extents of tumor were recorded. Results: One pat ient with a twice-recurrent DFSP had another recurrence after Mohs mic rographic surgery, for an overall local recurrence rate of 2% (zero fo r primary tumors and 4.8% for recurrent tumors). There were no cases o f regional or distant metastases. Macroscopic tumor size ranged from 0 .3 x 0.6 cm to 30 x 20 cm, whereas microscopic (postoperative) size ra nged from 1.8 x 1.0 cm to 35 x 40 cm. We calculated the likelihood tha t a given width of excision around the macroscopic tumor would clear t he entire microscopic extent of tumor. Standard wide excision with a w idth of 1 cm around the primary tumor would have left microscopic resi dual tumor in 70.7%; a width of 2 cm, 39.7%; 3 cm, 15.5%; and 5 cm, 5. 2%. Even an excision width of 10 cm would not have cleared the microsc opic extent of some tumors, despite taking a huge excess of normal tis sue. Conclusion: Treatment of primary and recurrent DFSP by Mohs micro graphic surgery results in a low recurrence rate because of the abilit y of the technique to permit the detection and excision of microscopic tumor elements in even the most asymmetric tumors. Whatever type of s urgery is chosen to treat DFSP, it is necessary to assess the entire p erimeter of the tumor for microscopic extension and to achieve tumor-f ree margins in all directions.