Fibroadenomas are the most common benign breast tumors, in which carcinoma rarely develop. We report the imaging findings of an invasive ductal carcinoma arising within the existing fibroadenoma in a 34-year-old young lady. It was diagnosed pre-operatively under suspicious mammographic findings and the malignant diagnosis was confirmed by excision biopsy. The mass showed an explosion of large popcorn-like calcifications with nests of fine pleomorphic calcifications therein, a lobular shape and an obscured margin. The calcifications in the mammogram correlated with histology so well to make the definitely pre-operative diagnosis possible. This case also reminds us that radiologists should always pay attention to the associated malignant imaging characteristics whenever a mass demonstrates typical benign looking calcifications.