TT-702 in Patients With Advanced Solid Tumours.

TT-702 is a 'small molecule prodrug'. TT-702 is converted into TT-478, which then targets and blocks the function of the 'A2B adenosine receptor'. It is hoped that by blocking this receptor the immune system will become more active in recognising and removing tumour cells. This clinical trial has two phases: * Phase I, dose escalation phase - groups of patients will receive increasing doses of TT-702 to find an optimal dose that best targets the tumours. This phase will consist of both monotherapy and combination escalation cohorts. In the combination escalation cohorts, TT-702 will be evaluated in combination with an anti-PD-1/PD-L1 agent to be assessed in patients with Mismatch Repair deficiency (MMRd) tumours or patients with non-MMRd tumours in one of the following subtypes: colorectal cancer (CRC), metastatic castration-resistant prostate cancer (mCRPC), non-small cell lung cancer (NSCLC), pancreatic ductal adenocarcinoma (PDAC), triple-negative breast cancer (TNBC). * Phase II, expansion phase - larger groups of patients will receive the selected dose of TT-702 considered to be optimal in the Phase I, dose escalation phase. This phase will consist of one monotherapy expansion cohort and one combination expansion cohort. In the combination expansion cohorts, TT-702 will be evaluated in combination with an anti-PD-1/PDL1 agent. Potential agents for further combination expansion cohorts have not yet been defined. The main aims of this trial are to: * Find the maximum dose of TT-702 as a monotherapy and in combination with other anti-cancer drugs that can be given safely to patients. * Define the side effects of TT-702 and how these can be managed. * Determine the pharmacokinetics (PK) and elimination kinetics of TT-702.