Collision tumours: our recent experience.

Introduction: Collision skin lesions (CSL) are rare clinical and pathological entities, posing significant diagnostic and therapeutic challenges. These lesions comprise at least two distinct cell populations - benign and/or malignant neoplasms - that are adjacent yet clearly demarcated. CSL were categorized as collision tumours into three types: two benign lesions, one benign and one malignant lesion, and two malignant lesions, with the most common being basal cell carcinoma (BCC) and melanocytic naevus. Aim: To analyse and present cases of collision skin lesions treated surgically in our Dermatosurgical Unit. Material and methods: A retrospective review was conducted on patients treated in our unit in 2021-2022, excluding lesions arising from preexisting conditions or located at the same anatomical site but separable upon examination. Results: Out of 838 patients, 4 cases of collision tumours were identified: one with two benign lesions and three with one benign and one malignant lesion, all histologically confirmed. Conclusions: Collision tumours, due to their rare occurrence and complex nature, represent a diagnostic challenge. Awareness and early detection, aided by dermoscopy, are crucial for effective management. Treatment should prioritize the more aggressive component of the tumour, with excisional biopsy being a favourable approach. Further research is needed to better understand the pathogenesis and optimize diagnostic and therapeutic strategies.