This clinical trial is focused on studying a type of prostate cancer known as Metastatic Castration Resistant Prostate Cancer (mCRPC). This is a form of prostate cancer that continues to grow and spread even when the amount of male hormones in the body is reduced to very low levels. The study is testing a new treatment combination of two drugs: Capivasertib and Docetaxel. Capivasertib, also known by its code name AZD5363, is taken as a film-coated tablet, while Docetaxel is given as a solution for infusion, which means it is administered directly into the bloodstream through a vein.

The purpose of the study is to compare the effectiveness and safety of the combination of Capivasertib and Docetaxel against a combination of a placebo and Docetaxel in treating patients with mCRPC. A placebo is a substance with no active drug, used to compare the effects of the actual drug. Participants in the study will be randomly assigned to receive either the Capivasertib and Docetaxel combination or the placebo and Docetaxel combination. The study will be conducted in a double-blind manner, meaning neither the participants nor the researchers will know who is receiving the actual drug combination or the placebo combination.

Throughout the study, participants will receive regular treatments and will be monitored closely by the research team. The main goal is to assess the overall survival of patients, which refers to the length of time from the start of the study until death from any cause. The study will also look at other factors such as the progression of the cancer, changes in pain levels, and any side effects experienced by the participants. The study is expected to continue until December 2026, with the aim of providing valuable information on the potential benefits of Capivasertib in combination with Docetaxel for treating mCRPC.