Clinical and Experimental Dermatology

Interdigital squamous cell carcinoma in situ successfully treated with modified Mohs micrographic surgery and a split-thickness skin graft S.-G. Roh,1 J.-I. Kim,2 D.-W. Kim,2 S.-R. Hwang,2 S.-K. Yun,2,3 H.-U. Kim2,3 and J. Park2,3 Departments of 1Plastic and Reconstructive Surgery and 2Dermatology, Chonbuk National University Medical School, Research Institute of Clinical Medicine of Chonbuk National University, Jeonju, Korea; and 3Biomedical Research Institute of Chonbuk National University Hospital, Jeonju, South Korea doi: 10.1111/ced.12466

Squamous cell carcinoma in situ (SCCIS), or Bowen disease, is a premalignant condition that can progress into invasive squamous cell carcinoma (SCC). The interdigital space of the foot is one of the rarest locations of this tumour, with only six cases reported in the literature.1–3 SCCIS can easily be confused with tinea pedis or eczema, which can delay in diagnosis. In addition, treatment of a tumour in this location is limited by the unique anatomical characteristics. We report a case of interdigital SCCIS of the foot that was successfully treated with modified Mohs micrographic surgery (MMS) and a split-thickness skin graft (STSG). A 64-year-old woman presented with a 5-year history of an asymptomatic, well-demarcated, erythematous scaly patch limited to the left third interdigital space of her foot. She had been receiving topical antifungal treatment at a local clinic for several months, but the lesion had not improved. Although mycological examination results including potassium hydroxide examination and fungus culture were negative, the clinical features of the lesion were highly suspect for webspace infection. Therefore, the patient was initially treated with oral antifungals, antibiotics and potassium permanganate solution for 2 weeks, but no improvement was seen, and she was then lost to follow-up. When the patient returned to us over 1 year since her previous visit, the lesion had extended to the dorsal part of the third and fourth toes, and was painful. Physical examination revealed a sharply delineated, Correspondence: Dr Jin Park, Department of Dermatology, Chonbuk National University Medical School, 20, Geonji-ro (Geumam-dong), Deokjin-gu, Jeonju, 561 712, South Korea E-mail: [email protected] Conflict of interest: the authors declare that they have no conflicts of interest. Accepted for publication 25 April 2014

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scaly, erosive, erythematous plaque with some brownish macules on the third interdigital space, and on the dorsa of the third and fourth toes of the left foot (Fig. 1a). Repeated mycological and bacterial culture test results were negative. Subsequently, we performed a skin biopsy of the lesion, which showed findings compatible with SCCIS. The rapidly growing interdigital tumour was excised with modified MMS, which utilized formalin-fixed, paraffin wax-embedded tissue for an improved interpretation of the histology. The tissue was excised to at least 3 mm depth, maintaining a margin of 2–3 mm from the tumour edge. The depth of the excision was based on the clinical extent of the neoplasm. Following removal, strict orientation and mapping of the specimen was performed, and it was delivered to the pathologist for processing and interpretation. The initial biopsy was diagnosed as SCCIS, but the final histological diagnosis was upstaged to invasive SCC. The skin defect was temporarily covered with synthetic wound dressings until complete excision was proven and the margins were clear of tumour after the first stage of MMS. Reconstruction was then performed by STSG harvested from the right thigh (Fig. 1b). These procedures provided satisfactory cosmetic and functional outcomes. During the 2-year follow-up period, no recurrence or digital deformity was observed (Fig. 1c). Various therapeutic options are available to treat SCCIS, depending on the number, extent and location of the lesions. The interdigital space of the foot has a narrow, concave shape with a lack of abundant skin. Although the optimal therapeutic method for interdigital SCCIS has yet to be determined, MMS has become the recommended treatment for single digital SCCIS, as it allows more immediate margin control than other options, and it has tissue-sparing benefits.4 MMS

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Figure 1 (a) Interdigital squamous cell carcinoma in situ showing a sharply delineated, scaly, erosive, erythematous plaque on the third

interdigital space along with the third and fourth toes of the left foot. (b) Modified Mohs micrographic surgery following reconstruction with a split-thickness skin graft on the third interdigital space of the left foot. (c) The affected area 2 years after the treatment.

has also been shown to result in lower recurrence rates than non-MMS treatments when treating SCCIS. In our case, the solitary interdigital SCCIS was treated by modified MMS, which allows microscopic confirmation of a negative surgical margin while sparing the maximum amount of tumour-free tissue. In this modified MMS, histological examination of the specimen is performed on wax-embedded sections. This has a disadvantage in that it is time-consuming to process compared with classic MMS;5 however, it is more accurate and allows clear surgical margins of the excised tumour. There may be an argument that SCCIS can be treated with less invasive methods, because the disease is relatively benign with a slow-growing nature, and there have been a few case reports showing spontaneous regression. Although no large-scale studies have evaluated the efficacy of less invasive treatments such as topical 5-fluorouracil, imiquimod or photodynamic therapy, the average clearance rate with these was approximately 69–100%, 73–93% and 50–100%, respectively.6 These nonsurgical approaches, therefore, appear to have some efficacy, but they have the disadvantages of prolonged treatment periods, questionable patient compliance, difficulty in histological confirmation, and difficulty in accessing the area. In addition, SCCIS has a rate of progression to invasive SCC of at least 3–5% and up to 10%, although the precise incidence is not known. In our patient’s case, the tumour was rapidly growing and was in fact confirmed as SCC by the final histological diagnosis. Therefore, we believe that modified MMS can be an effective method to treat interdigital SCCIS. In conclusion, physicians should be aware of the development of SCCIS in unusual locations, such as interdigital spaces, and early histopathological confirmation is required. Modified MMS can be an effective method to treat interdigital SCCIS.

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Learning points



SCCIS, or BD, is a premalignant condition with a 3–5% risk of progression to invasive SCC. • SCCIS of the interdigital space of the foot, which is one of the most covered areas of the body, is extremely rare, and diagnosis may be delayed because of its unusual location and benign appearance. • Treatment of interdigital SCCIS is difficult because of this location’s unique anatomical characteristics such as a narrow, concave shape, lack of abundant skin, and potentially poor wound healing. • Physicians should be aware of the development of SCCIS in unusual locations, such as the interdigital space. • Early histopathological confirmation is required. • In addition, MMS with skin grafting is an effective method to treat interdigital SCCIS.

References 1 Kendler M, Maschke J, Simon J et al. Interdigital squamous cell carcinoma in situ (Bowen’s disease): treatment with microscopically controlled surgery. J Eur Acad Dermatol Venereol 2008; 22: 763–5. 2 Masuda T, Hara H, Shimojima H et al. Spontaneous complete regression of multiple Bowen’s disease in the web-spaces of the feet. Int J Dermatol 2006; 45: 783– 5. 3 Liu GT, Lovell MO, Steinberg JS. Digital syndactylization for the treatment of interdigital squamous cell carcinoma in situ (Bowen disease). J Foot Ankle Surg 2004; 43: 419–22.

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4 Cox N, Eedy D, Morton C. Guidelines for management of Bowen’s disease: 2006 update. Br J Dermatol 2006; 156: 11–21. 5 Clayton BD, Leshin B, Hitchcock MG et al. Utility of rush paraffin-embedded tangential sections in the management of cutaneous neoplasms. Dermatol Surg 2000; 26: 671–8.

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6 Shimizu I, Cruz A, Chang KH et al. Treatment of squamous cell carcinoma in situ: a review. Dermatol Surg 2011; 37: 1394–411.

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Interdigital squamous cell carcinoma in situ successfully treated with modified Mohs micrographic surgery and a split-thickness skin graft.

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