11. Collision tumour: Amelanotic lentigo maligna and Atypical FibroXanthoma/Pleomorphic Dermal Sarcoma (AFX/PDS): A case report

Abstract

Background and aims: Collision tumours in the skin are unusual neoplastic events. They include carcinosarcoma, Merkel cell carcinoma with squamous cell carcinoma, basal cell carcinoma and Bowen’s disease and squamo-melanocytic tumour. Collision tumours involving lentigo maligna, malignant melanoma and AFX/PDS are extremely rare. Aims: Here we present a case of a collision tumour of lentigo maligna and AFX/PDS. Methods: A 90-year-old male presented with a scaly, erythematous plaque on the vertex of his scalp. The approximate size of the lesion was 15×12 mm. The clinical impression was Bowen’s disease vs basal cell carcinoma. The lesion was curetted followed by cautery. Results: The histological examination of routine H&E sections revealed horizontal proliferation of non-pigmented atypical cells in the basal layer of the epidermis with focal pagetoid infiltration of the suprabasal epidermis. The solar elastotic dermis showed sheets of markedly atypical round, oval epithelioid and spindle shaped cells with enlarged hyperchromatic nuclei and prominent nucleoli. Occasional mitotic figures were present. Immunohistochemically the atypical cells in the basal layer were strongly positive for SOX10 and S100. However, the dermal cells were strongly positive for CD10, CD68 and CD163 and negative for SOX10, S100, CKBS and P63. Morphological features and immunohistochemistry were consistent with a collision tumour composed of lentigo maligna and AFX/PDS. Conclusions: To the best of our knowledge the association between lentigo maligna and AFX/PDS has not been reported previously; however, we are aware of two reports of association between melanoma and AFX/PDS. Collision tumours of the skin can result in misleading clinicopathological presentation and appropriate diagnostic techniques with high index of suspicion and multiple immunohistochemical stains are essential for precise diagnosis and management.