Tumour-to-tumour metastasis is a rare phenomenon, but has been described in the literature in just over 100 cases. It can be particularly puzzling for the reporting pathologists, when encountered unexpectedly in a tumour showing abrupt transition from the usual morphology to another unusual pattern. The literature reports a variety of combinations with carcinoma-to-carcinoma being the most common; and renal cell carcinomas appear to the most common recipient tumours with common donor tumours being breast, lung and renal cell carcinomas. The authors report a case of poorly-differentiated lung carcinoma metastasising into a carotid body paraganglioma. Our case is unique and in our knowledge the first described case of carotid body paraganglioma with metastasis from a lung primary. To the best of our knowledge this is the first report of this interesting biological phenomenon in this combination.
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