Abstract
Phyllodes tumors (PTs) and Metaplastic Malignant Spindle Cell Carcinoma (MMSCC) are rare and challenging breast malignancies. MMSCC is even rarer and highly aggressive. Surgical excision is the mainstay of treatment for both, but MMSCC generally carries a poorer prognosis. A 46-year-old woman with a history of breast augmentation 4 years ago presented with a rapidly progressing right breast mass. Imaging and core biopsy suggested a malignant PT. A right mastectomy with latissimus dorsi flap reconstruction was done. Initially diagnosed as a malignant PT, the post-operative pathology revealed a co-existence of malignant PT and MMSCC, an extremely rare finding. This case reports the unique challenge of a patient harboring both malignant PT and MMSCC within the same breast tissue. This exceedingly rare co-existence emphasizes the diagnostic complexities associated with uncommon breast malignancies. Our case highlights the challenges of diagnosing and managing uncommon and aggressive breast malignancies.