CA9 and hereditary clear cell renal cell carcinoma: Several examples of off-tumor responses in clinical trials are as follows: in renal cell carcinoma, targeting carbonic anhydrase IX (CAIX) led to liver toxicity in 4/8 patients in 2/3 cohorts due to basal expression of CAIX on bile duct epithelium even with low doses of CAR T cells (24, 25).