Retroperitoneal Metastasis from Lobular Carcinoma of the Breast: A Case Report

This is a case report of a 50-year-old woman with bilateral lobular breast carcinoma. Staging imaging revealed diffuse thickening of the retroperitoneal fasciae, involving both renal hila and resulting in bilateral hydronephrosis, as seen in MRI. along with metastatic bone involvement. Notably, FDG-PET-CT showed no increased metabolic activity in the retroperitoneum. Because of the indeterminate nature of the retroperitoneal thickening, an ultrasound-guided biopsy of the retroperitoneal thickening was performed, which confirmed metastatic involvement by invasive lobular carcinoma. The literature demonstrates that lobular carcinoma has a higher propensity to metastasize to the peritoneum, retroperitoneum and gastrointestinal tract, compared to invasive ductal carcinoma. This case report highlights the importance of the clinical manifestations and subtle radiological findings of peritoneal and retroperitoneal spread of ILC.