The medullary thyroid carcinoma (MTC) is an unusual malignant neoplasm with a high rate of metastasis. It usually appears as a single nodule in more than 70% of the cases, and the main distant metastasis sites are liver, lung, and bone. Breast metastasis is rare because within the mammary tumours only between 0.2% and 1.3% are secondary tumours. MTC is strongly associated with the multiple endocrine neoplasia sub-type 2B (MEN2B), which is a dominant autosomal disorder characterised by the presence of MTC and phaeochromocytoma in the absence of hyperparathyroidism. Metastasis from a MTC to the breast in the context of a MEN2B rarely occurs, which is why this case is being reported.