Two cases of lobular breast carcinoma metastatic to an endometrial polyp are described. Both patients had been treated with tamoxifen and presented with abnormal uterine bleeding. Histology of endometrial biopsy in both cases showed typical tamoxifen-associated endometrial polyps with focal subtle stromal infiltration by metastatic lobular breast carcinoma. This was confirmed by positive immunohistochemical staining with cytokeratin epithelial markers. Metastatic breast carcinoma may rarely involve tamoxifen-associated endometrial polyps. Because primary endometrial carcinomas may also arise within tamoxifen polyps, these should be extensively sampled. We briefly review polypoid uterine lesions that may occur secondary to tamoxifen therapy.