This pictorial essay presents the common radiological (mammography and/or ultrasonography) and pathological findings observed in unusual malignant breast lesions, which include well-differentiated subtypes of invasive ductal carcinoma not otherwise specified (tubular, mucinous, papillary, and medullary carcinomas), metaplastic carcinoma, and metastases. This study also includes unusual ultrasonographic appearances of a plasmacytoma.