Malignant transformation of post-radiation induced erosive lichen planus to squamous cell carcinoma.

Radiation therapy is commonly used to treat various types of malignancies during or after radiation. Approximately 95% percent of patients develop common skin manifestations including dermatitis, atrophy and fibrosis. Rare manifestations, including non-melanoma skin cancers, morphea, cutaneous angiosarcoma and bullous pemphigoid, have been reported post-treatment. The development of lichen planus (LP) from radiation therapy is exceedingly rare, with only 14 previous cases reported. Of these, none were associated with malignant transformation. Malignant transformation from LP is uncommon, with reported cases mainly in oral manifestations of LP at rates of ∼1%-2%. Classic cutaneous manifestations of LP have not been associated with an increased risk of malignancy. We report a unique case of erosive cutaneous LP with malignant transformation in a previously radiated site. Our case highlights a novel cutaneous adverse event to radiation treatment and emphasises the importance of considering erosive LP on the differential when evaluating recalcitrant erosions in a previously radiated area and to monitor closely for transformation to squamous cell carcinoma.