Metaplastic carcinoma of the breast is rare. We report a case in a 53-year-old womanwho presented with a rapidly-growing breast mass. The lesion had a complex echogenicity in ultrasonography and a high signal intensity in a T2-weighted image with rim enhancement in contrast-enhanced MR images. The PET/CT images showed high uptake for the lesion. The lesion was biopsied and found to be a metaplastic carcinoma with an adenomyoepithelioma component. Although metaplstic carcinoma was difficult to differentiate from other common breastcancers, it showed complex echogenicity on ultrasonography and high signal intensity on a T2 weighted image with rim enhancement on contrast-enhanced MR images.