The present disclosure relates to tricyclic heterocyclic compounds that are inhibitors of BET proteins such as BRD2, BRD3, BRD4, and BRD-t, and are useful in the treatment of diseases such as cancer.本開示は、BRD2、BRD3、BRD4、及びBRD-tなどのBETタンパク質の阻害剤であって、癌などの疾患の治療に有用な三環式複素環化合物に関する。