RESUMEN
Refractory malignant ascites (MA) is a common complication in cancer patients. Renal cell carcinoma (RCC) is rarely present with peritoneal ascites, which is commonly associated with carcinomas of the gastrointestinal and female reproductive tracts; including especially ovarian high-grade serous carcinoma. Currently, chemotherapy and paracentesis represent the most widely used methods to relieve the symptoms. Recently, intraperitoneal therapy with catumaxomab-a trifunctional hybrid antibody-has been introduced for the treatment of MA. The benefit of this treatment has been demonstrated in patients with distinct abdominal malignancies. In this case report, we present the first case of successful catumaxomab treatment against MA in a patient with advanced RCC with sarcomatoid differentiation. After the second administration of catumaxomab, paracentesis became no longer necessary. Catumaxomab might represent a safe treatment option for MA in the course of metastatic RCC with sarcomatoid differentiation.