Case 8 Answer
Hamartoma. This large mass contains mixed fat and glandular tissue with well-defined margins. This is the appearance of a hamartoma (also known as a fibroadenolipoma). Sometimes referred to as a "breast within a breast," sometimes a "slice of salami", this finding is benign, and does not need further workup.
The other fat-containing masses should not be confused, because each has a distinctive appearance on mammography. See the related cases below.