Epidermal cysts are common skin tumors. In order to achieve cost-effectiveness, routine biopsy is not recommended in the setting of plastic surgery [
1]. We report a case of squamous cell carcinoma (SCC) confirmed in a residual wound after resection of a cutaneous cyst. A 46-year-old male patient underwent local resection of a cystic lesion in the left nasal alar region 3 weeks before at a local medical center without biopsy. He developed tenderness, fever, and erythema over the wound, and visited our hospital (
Fig. 1A). While the planned excision was performed, a 0.8×0.9-cm-thick white capsule was observed (
Fig. 2). Therefore, a biopsy including skin tissue was performed. A SCC was then diagnosed (
Fig. 3), and additional resection with a 5-mm safety margin was performed. During the 18-month follow-up period, no recurrence was observed (
Fig. 1B). Owing to the rarity of SCC arising from epidermal cysts, the nature and mechanism of this phenomenon remains uncertain. Malignant change of an epidermal cyst is suspected when a chronic wound shows a sudden increase in size and ulceration. In such cases, other authors have suggested that biopsy and complete excision with a pathological examination should be performed [
2]. According to a recent study, reported cases of SCC from epidermal cysts have increased [
3]. Thus, to exclude malignant tumors, a biopsy is recommended when epidermal cysts with recurrent ulcers show wall thickening.