Intra-abdominal desmoid tumor following retroperitoneal lymph node dissection for testicular germ cell tumor

In the testicular cancer post-treatment setting a rapidly growing retroperitoneal mass leads to a differential diagnosis including recurrent germ cell tumor, residual mature teratoma, or sarcomatoid degeneration. We report the case of a 27-year-old man with a large abdominal mass occurring in the setting of a mixed germ cell tumor after radical orchiectomy with primary chemotherapy followed by retroperitoneal lymph node dissection. Surgical excision of this mass followed by pathological review revealed an intra-abdominal desmoid tumor. Fluorescence in situ hybridization (FISH) for isochromosome 12p failed to demonstrate a germ cell tumor origin. This is the fourth such case of an intra-abdominal desmoid tumor after retroperitoneal lymph node dissection for testicular cancer in the urologic literature. This case highlights the need for careful consideration of a desmoid tumor when a rapidly growing spindle cell tumor is encountered in a post-treatment testis cancer patient.