Collision malignant melanoma and medullary carcinoma of the thyroid

This report presents the case of a 54‐year‐old woman with a collision tumour of malignant melanoma and medullary thyroid carcinoma in the thyroid. Twenty four of 25 neck lymph nodes contained metastatic melanoma, with the rest having both metastatic melanoma and medullary carcinoma. Systemic chemotherapy was administered for the malignant melanoma, and a complete response was thus obtained. However, just after having the chemotherapy, multiple lung and brain metastases emerged. The simultaneous occurrence of malignant melanoma and medullary carcinoma in the same thyroid has not been previously reported in the literature. Collision tumour of malignant melanoma and medullary carcinoma of the thyroid might imply bad prognosis.