A 63-year-old woman was referred to our hospital for breast cancer treatment. She had a large HER2-positive breast tumor on her left breast, and received neoadjuvant chemotherapy. After treatment, a shrunk spiculated mass with calcification-like high density was detected on mammography, and MRI revealed a large strong susceptibility artifact. Surgical specimen analysis attributed these imaging features to a large marked hemosiderin deposition. This case is herein reported due to its rarity and to the importance of acknowledging that this large marked hemosiderin depositions can present as a calcification-like high density on mammography and shows large susceptibility artifact on MRI imaging.