Subungual Squamous Cell Carcinoma in a Patient with Psoriasis.

Subungual squamous cell carcinoma (SCC) is a rare malignant tumour with an indolent course and unknown aetiology. It is usually misdiagnosed as a benign lesion, resulting in delayed treatment. Although psoriasis is not a precancerous skin condition, the treatment modalities cyclosporine and psoralen with ultraviolet A (PUVA) might increase the risk of developing cutaneous SCC, although a relationship has not been confirmed. We describe a patient with psoriasis who had been treated with cyclosporine and PUVA 6 years previously. He developed back SCC 2 years later, a subungual skin lesion after another 2 years and presented to us 1 year later, when nail elevation and biopsy revealed SCC. LEARNING POINTS: Subungual squamous cell carcinoma (SCC) is often misdiagnosed as a benign condition so most cases are invasive by the time of diagnosis; nail elevation and biopsy are recommended in all suspicious cases.Although psoriasis is not an independent risk factor for subungual SCC, the cyclosporine and PUVA used to treat psoriasis are risk factors for cutaneous SCC.The aetiology for subungual SCC is still unclear, but it should be suspected in patients with psoriasis and a suspicious presentation. © EFIM 2020.