Collision tumour of the breast composed of Merkel cell carcinoma and invasive ductal carcinoma: a case report.

We report a case of a 71-year-old female with a palpable breast mass. Pathologic evaluation of the breast mass showed a unique collision tumour with a high-grade invasive and in-situ ductal carcinoma component and a high-grade neuroendocrine carcinoma component. The neuroendocrine component turned out to be Merkel cell carcinoma (MCC), with immunohistochemical confirmation. To the best of our knowledge, this is the first case report of a collision tumour with ordinary ductal carcinoma and MCC in the breast.