This is 2 part study: Part A and Part B. Part A of the study consists of a screening period and 3 treatment periods (midazolam alone, capivasertib alone, and midazolam + capivasertib). During Part A, the PK profile of midazolam will be determined with and without capivasertib.All participants will receive capivasertib treatment (4 days on/3 days off); however, at the Investigator's discretion, ER positive breast cancer patients may also receive fulvestrant in addition to capivasertib and midazolam. Participants completing Part A without disease progression or unacceptable toxicity, who are considered likely to continue to benefit from further capivasertib treatment (with or without certain standard of care treatment) in the opinion of the Investigator will enter Part B. Part B of the study consists of an extended treatment period with capivasertib, with or without certain standard of care treatment, followed by a 30-day safety follow-up.~Part A of the study may be extended to allow the administration of midazolam on a rescheduled Cycle 1 Day 8(C1D8) and Cycle 1 Day 12(C1D12 ) visit.
This is an open-label, fixed-sequence study to evaluate the effect of capivasertib on the pharmacokinetics (PK) of midazolam, a sensitive CYP3A substrate. The PK of midazolam will be assessed when administered alone and in combination with repeated doses of capivasertib.