Concurrent retroperitoneal schwannoma and phyllodes tumor: a rare presentation of synchronous primary tumors: a case report

Retroperitoneal schwannomas represent 0.3–3.2% of schwannomas and 1–5% of retroperitoneal tumors. Phyllodes tumors comprise 0.3–0.5% of breast neoplasms. Both are extremely rare tumors. Their synchronous occurrence has not been reported in the existing literature. A 48-year-old Pakistani woman of Punjabi ethnicity presented with chronic lumbar pain and a right breast lump. Imaging revealed a retroperitoneal mass below the left kidney and a large lobulated breast lesion. Biopsies from both lesions were performed, but did not yield definitive diagnoses, requiring further investigation. Synchronous excision was performed. Histopathology confirmed a benign retroperitoneal schwannoma and a benign phyllodes tumor. The patient recovered well and remained recurrence-free at six months. This is the first reported case of concurrent retroperitoneal schwannoma and phyllodes tumor. Both entities are difficult to diagnose prior to surgery as imaging and core biopsies may be inconclusive, often necessitating excisional histopathology for definitive diagnosis. This case highlights the importance of comprehensive evaluation and multidisciplinary management to facilitate safe single-stage excision, while underscoring the need for long-term surveillance and consideration of potential genetic predisposition.