Late breast recurrence of plasmablastic lymphoma with apparent partial spontaneous regression.

Plasmablastic lymphoma (PBL) is an uncommon, highly aggressive lymphoma with a predilection for extranodal involvement. Secondary breast involvement is exceedingly rare and can closely resemble primary breast malignancy on imaging. We present a 60-year-old woman with a remote history of sinonasal PBL in long-term remission who developed a rapidly enlarging right breast lump nearly two decades later. Initial breast imaging identified a highly suspicious lesion suggestive of malignancy, and ultrasound-guided core needle biopsy confirmed disease recurrence. Follow-up imaging performed one month later unexpectedly showed apparent partial spontaneous regression of the lesion. However, subsequent metabolic imaging identified widespread disease. This case highlights the diagnostic complexity of breast involvement by PBL and the importance of accurate histopathological subtyping for prognostic assessment. It also emphasizes the value of integrating functional and morphologic imaging for accurate disease evaluation and optimal management.