Clinical, Dermoscopic and Microscopic Features of a “Collision Tumour” Ultimately Confirmed as a Regressing Melanoma – Lessons Learnt from a Chance Diagnosis

Spontaneous regression of malignant melanoma was first reported over a century ago. Clinically, areas of blue or grey colouration in lesions may be indicative of regression. Dermoscopy is a very useful tool for diagnosing regression. An important criterion is the blue-white scar. About 10–35% of excised melanomas show features of regression histopathologically. We present a case of regressing melanoma, with clinical and dermoscopic features suggesting a collision tumour, diagnosed histopathologically. This case might improve our knowledge of the potential clinical manifestations, and the biology, of regressing melanoma.