Additional Study Information: The main purpose of the study is to find the optimal dose of HRO761 alone or in combination with tislelizumab or irinotecan that can be given to people with certain cancer types called MSI high or dMMR. The new drug being tested in the study, HRO761, is an oral drug that is called a targeted medicine: this means that it targets particular processes which may not be working properly in the cancer cells in a participant's body and causing their disease. This is the first time HRO761 is given to people and the first time HRO761 is used in combination with tislelizumab or irinotecan. Tislelizumab has been used in other cancer studies in the past few years and irinotecan is a drug approved to treat certain types of cancer. Cancer includes: bladder cancer, breast cancer, colon and rectal cancer, esophageal cancer, gynecologic cancers, head and neck/oral cancer, liver cancer, lung cancer, skin cancers, pancreatic cancer, prostate cancer, stomach cancer, testicular cancer, and thyroid cancer.