Compounds of formula (I)
wherein R
1
to R
8
, A, B, Z
1
, and Z
2
are as defined in the claims and pharmaceutically acceptable salts and esters thereof are disclosed. The compounds of formula (I) possess utility as androgen receptor antagonists (inhibitors) and/or cytochrome P450 monooxygenase 17α-hydroxylase/17,20-lyase (CYP17) inhibitors. The compounds are useful as medicaments in the treatment of cancer, particularly prostate cancer, and other androgen dependent conditions and diseases where androgen antagonism is desired.