Diagnostically challenging case of low‐fat spindle cell lipoma

right calf (Fig. 1a). Histopathology showed hyperkeratosis and marked acanthosis with full-thickness proliferation of dysplastic cells, loss of maturation and lack of cell polarity. Inflammatory cell infiltration of lymphocytes was observed in the upper dermis (Fig. 1b). The patient was diagnosed with BD. Considering the patient’s age and preference for non-surgical treatment, we attempted topical application of ingenol mebutate 0.05% gel with the institutional review board’s approval. We applied ingenol mebutate 0.05% gel on the affected area with a 0.5-cm margin once daily for 3 days consecutively. One day after the first application, we observed multiple vesicles overlying an erythematous background beyond the treated area. Local skin reactions including erythema, vesicles, erosion and ulceration, as well as a moderate degree of pain at the application site peaked between day 3 and 6. The ulceration was managed with daily wet dressing and hydrophilic polyurethane foam, and it healed completely with residual postinflammatory hyperpigmentation by day 12. Ten weeks after the treatment, all the lesions were clinically resolved (Fig. 1a); multiple skin punch biopsies showed no evidence of recurrent BD (Fig. 1b). At the time of writing this report (i.e. 6 months after the treatment), there has been no recurrence. Ingenol mebutate 5% gel is a new topical drug extracted from the latex sap of a plant, Euphorbia peplus, which has been used for centuries as a natural folk remedy for warts, corns and cancerous lesions. Clinical studies have proven it to be safe and efficacious, leading to the US Food and Drug Administration approval of this chemotherapeutic agent for field therapy of actinic keratosis in 2012. Topical ingenol mebutate gel was generally well tolerated in the treatment of patients with actinic keratoses, with the majority of adverse events being of mild to moderate severity including erythema, scaling, crusting, swelling, vesiculation/pustulation and erosion/ ulceration. Ingenol mebutate has a dual mode of action, facilitating cell necrosis, and on the other hand, producing antibodies against the tumor, resulting in the destruction of dysplastic cells. Topical ingenol mebutate gel has begun to show effectiveness against superficial basal cell carcinoma. This is the first histologically proven case of BD successfully treated with ingenol mebutate 0.05% reported in the published work. We suggest that ingenol mebutate 0.05% gel could be a potentially effective and safe treatment option for BD, with a short treatment course, successful efficacy and cosmetic outcomes.