Without proper and timely diagnosis and management, SC can cause severe patient morbidity. Although SC rarely metastasizes and can have an indolent course, it can be locally de-structive and lead to potentially disfiguring outcomes.5-7 SC can invade deeply and infiltrate into the dermis, subcutaneous fat tissue, muscle, perichondrium, periosteum, and galea.8 Goto et al9 reported a case of an SC that was initially misdiagnosed as a basal cell carcinoma of the left middle finger. The deeper, characteristic features of SC were not recognized until after the affected finger required amputation due to erosion of the bone. Hoppenreijs et al11 described an aggressive case of an SC arising at a site of previously irradiated squamous cell carcinoma of the lower eyelid. Extensive involvement of the SC in the orbit led to the recommendation of an orbital exenter-ation; however, it was not performed because of the poor clinical condition of the patient. Treatments for SC have included wide local excision and Mohs micrographic surgery (MMS). SC treatment with wide local excision often resulted in incomplete excision of the neoplasm despite having taken an adequate margin around the clinically assessable tumor.5 Cases of SC treated with wide local excision had a recurrence rate of 47%.5 The positive surgical margins following wide local excision may be due to the deep infiltration of SC, which frequently exceeds the clinically predicted size of the tumor.5 Due to the close relationship of MAC and SC, we feel that MMS treatment of SC will reduce recurrences as it has for MAC. Currently, there is strong support for the treatment of MAC with MMS as a gold standard to ensure complete clearance of the neoplasm and to reduce the local recurrence rate.12,13,17,21,22,37,38 In a study of MAC by Chiller et al,37 the authors demonstrated a median 4-fold increase in defect size when they compared the clinically estimated pretreatment size of the lesion with the MMS-determined posttreatment size of the lesion. The authors therefore suggest that, similar to the MMS-treated lesions, the lesions completely treated with wide local excision also would produce a defect size that is at least 4 times greater than the predicted pretreatment size of the lesion. Because wide local excision relies on predicted margins of the lesion, which the authors have shown can be greatly underestimated, Chiller et al37 argue that the use of MMS, which does not rely on predicted margins, is a reasonable first-line therapeutic modality for effectively treating patients with MAC. Furthermore, MMS allows for the examination of the entire peripheral and deep margins of the lesion, which is critical when considering the deep infiltrative nature of MAC. The reported local recurrence rate of MAC treated with MMS is 0% to 5%,12,13,21,26,38 which is much lower than the reported local recurrence rate following treatment with wide local excision. This reduced recurrence rate found in MAC cases treated with MMS is probably due to the ability to confirm complete removal of the neoplasm with MMS.
Conclusion To our knowledge, this case report describes the occurrence of SC, a rare sweat gland neoplasm, in the youngest reported patient and is only the second reported case of SC treated with MMS. Adequate sampling of tissue with an excisional biopsy allowed for appropriate evaluation with histologic and immunohistochemical studies to arrive at the diagnosis that could easily have been missed with a superficial biopsy. In our patient, histopathologic evaluation showed typical nests of basaloid cells, ductal differentiation, and ductal fibrosis seen in SC. However, perineural involvement that is particularly characteristic of SC was not present. This may portend a better prognosis for our patient whose tumor was completely excised after one stage of MMS and has not shown evidence of recurrence at the 18-month follow-up visit. MMS allowed for evaluation of the entire surgical margin and decreased risk of local recurrence resulting from an incomplete excision. In addition, it also allowed for sparing of normal tissue in a cosmetically sensitive area where SC commonly occurs. In summary, this case highlights the importance of including SC in the differential diagnosis of an enlarging cystic lesion in a younger patient and its successful treatment with MMS.