STAT3 and in situ carcinoma: STAT3 is implicated in a plethora of cellular events, and activation of STAT3 also plays a key role in the malignant transformation of urothelial progenitor cells, the formation of carcinoma in situ (CIS) and progression to the muscle-invasive cancer following treatment with the carcinogen N-butyl-N-(4-Hydroxybutyl) nitrosamine (BBN) in an animal model [47].