erythroplasia of Queyrat is also considered an indication for MMS when located in high-risk anatomical areas such as the face or genitalia or in cases where the lesion diameter is greater than 2 cm [4]. Most recently, Hansen et al. reported a 6.3% 5-year recurrence rate for 83 SCC in situ tumors [11]. A similar recurrence rate for 95 patients with SCC in situ who completed 5 years of follow-up also had a 6.3% recurrence rate [12].

Summary: Uncommon Indications

•The uncommon indications include Dermatofibrosarcoma Protuberans (DFSP), Microcystic Adnexal Carcinoma (MAC), Atypical Fibroxanthoma (AFX), Malignant Fibrous Histiocytoma (MFH), Sebaceous Carcinoma (SC), Merkel Cell Carcinoma (MCC), Melanoma, and Superficial Leiomyosarcoma.

•The evidence underlying the indication for these tumors is limited by smaller numbers of subjects when comparing standard surgical excision and Mohs micrographic surgery.

2.3Uncommon Indications

2.3.1Dermatofibrosarcoma Protuberans (DFSP)

DFSP begins as a slow-growing plaque that is often skin colored. It continues to grow forming firm nodules that are red or brown in color and is comprised of spindle cells that are thought to be of fibroblastic origin. A number of small case reports and series have demonstrated recurrence rates when using MMS for DFSP to be 0–10% [13–21].

Only 3 studies in the literature have specifically compared MMS versus WLE for the treatment of DFSP. Gloster and colleagues reported 84 patients with DFSP comparing Wide Local Excision (WLE) versus MMS, with only 15 being treated by MMS [22]. They found a 6.6% recurrence rate for DFSP treated by WLE and a 10% recurrence rate for DFSP treated by MMS after 36 months of follow-up for the WLE group and 40 months of follow-up for the MMS

group. It should also be noted that 56% of the tumors in this study were recurrent.

DuBay and colleagues reported results from 63 cases of DFSP comparing WLE versus MMS with only 11 patients being treated with MMS [23]. A fol- low-up of more than 4 years revealed that none of the tumors in either group had recurred.

Meguerditchian et al. compared MMS to WLE in 48 patients. 28 underwent WLE, while 20 were treated with MMS. At a median follow-up time of 49.9 months for the WLE group, 1/28 (3.6%) recurred, while 0/20 (0%) recurred in the MMS group at a median followup time of 40.4 months [24].

2.3.2Microcystic Adnexal Carcinoma (MAC)

MAC usually develops as a flesh-colored plaque. It is most commonly observed on the head and neck (90% of cases) and more specifically on the cheek (27.3%). Perineural invasion is common and is more prevalent in recurrent tumors [25–27]. MAC is regarded as a locally aggressive tumor with little metastatic potential [28, 29]. The tumor is comprised of epithelial cords within a fibrotic stroma that can invade deeply into the dermis, subcutaneous tissue, and even to skeletal muscle. It is commonly misdiagnosed as BCC and SCC [27].

Standard surgical excision of MAC results in up to a 60% recurrence rate, although considerable variation has been noted [25, 27, 30–32]. MMS has been associated with much lower recurrence rates from 0% to 12% [26, 33–36].

2.3.3Atypical Fibroxanthoma (AFX)

AFX presents as a rapidly growing solitary nodule on the head and neck of elderly males that may be up to 2 cm in diameter [37]. The tumor is composed of pleomorphic spindle, epithelioid, and histiocyte-like cells found in the dermis. There are also rare variants of clear cell, granular, and sclerotic atypical fibroxanthomas. In a review of 91 patients with 93 tumors, Ang and colleagues reported an overall recurrence rate of 0% for MMS (59 tumors) and 8.7% for WLE (23 tumors) with a median follow up of 8.7 years [37]. Hunter et al. found a recurrence rate of 6.9%

for MMS and 16% for other surgical methods [38]. Davis et al. reported 0/25 recurrences using MMS with a mean follow-up of 29.6 months and 3/25 recurrences using WLE with a mean follow-up of 73.6 months [39].

2.3.4Superficial Leiomyosarcoma

Superficial Leiomyosarcoma is a rare cutaneous sarcoma that hardly ever metastasizes [40] but has a predisposition towards recurrence. The prognosis is much better compared to soft-tissue and deep leiomyosarcomas [40]. It presents as a red nodule often located on a nipple or extremity that can sometimes be painful [40]. The tumor is comprised of densely packed smooth muscle cells thought to be derived from the arrectores pilorum muscle [41]. The known recurrence rate following MMS is 14%, and for WLE, it is also 14% [38]. The tumor may act more aggressively in patients who are immunosuppressed, and clearly, more investigation needs to occur to determine the optimum treatment in those circumstances [42].

2.3.5Malignant Fibrous Histiocytoma (MFH)

MFH most commonly presents as a nodule on the lower extremities [43]. When using traditional WLE for MFH, recurrences rates range from 30% to 40% [44, 45]. The sparse amount of literature regarding MMS demonstrated a 43% (3/7) recurrence rate over a mean of 3.8 years [38].

2.3.6Sebaceous Carcinoma (SC)

SC is thought to arise from the Meibomian glands or glands of Zeiss [40, 46]. It most commonly presents as a slow-growing, yellow nodule on the upper eyelid of elderly women [40]. Blepharoconjunctivitis or chalazion are common misdiagnoses [40]. An extraocular form also exists and tends to present as a pink to red nodule that sometimes bleeds [47]. It was once believed that the metastatic potential of extraocular SC was lower than ocular SC; however that concept is currently under debate [48–52]. The tumor is histologically composed of irregular lobules of sebaceous cells with a foamy

cytoplasm. It can histologically be confused with Basal Cell Carcinoma, especially BCC with sebaceous differentiation, and can be differentiated using an oil red O stain or Thomsen-Friedenreich (T) antigen [53, 54]. The current standard surgical excision is 5–6 mm margins with recurrence rates of 9–36% at 5 years with a mortality rate of 18–30% [55–57]. Most of the cases treated by MMS have been reported as case reports and case series. One group found an 11.1% recurrence rate when using MMS with a 3-year follow-up from 18 patients [58]. In rare cases, SC may grow in a noncontinuous fashion [47], and so MMS may not be the best surgical option in that circumstance. Although MMS appears to be promising for SC, more studies are needed to determine the exact feasibility in the treatment of SC.

2.3.7Melanoma

A number of variations on staged surgical excision and MMS have been investigated. Dr. Zitelli and colleagues reported a 5-year recurrence rate of 0.5% using MMS for 553 tumors. This rate is equivalent to and, in some cases, better than the standard surgical excision [59]. Recently, a new 20-min MART-1 immunostaining protocol has been developed which greatly assists in evaluating frozen sections. In addition, a nuclear stain known as MITF may be helpful when used in combination of MART-1 to more closely delineate the surgical borders. There is currently a large amount of debate as to the feasibility of MMS for melanoma given the artifactual changes that occur to atypical melanocytes in frozen sections. MMS with immunohistochemistry is a very promising technique, but its evidence base is mainly limited to case reports and series.

2.3.8Merkel Cell Carcinoma (MCC)

MCC presents as a solitary, purple, dome-like, firm nodule on the head, neck, or extremities up to 4 cm in diameter. Histologically, the tumor is comprised of small round blue cells in a nested or trabecular pattern. These tumors have a high rate of recurrence and metastasis [60]. The prognosis of MCC is considered worse than malignant melanoma [61]. A 62% survival rate over 3 years has been reported [62]. The persistence rates using WLE versus MMS are 31.7% (13/41) and 8.3% (1/12), respectively [63]. The group undergoing