Rucaparib is primarily used in the treatment of certain types of cancer, particularly ovarian cancer, fallopian tube cancer, and primary peritoneal cancer. It is especially effective for patients with BRCA mutations, as it works by inhibiting the PARP enzyme, which helps repair DNA damage in cancer cells. By blocking PARP, the drug prevents cancer cells from repairing their DNA, leading to their death. It is often prescribed for patients who have already undergone chemotherapy and need maintenance therapy to prevent cancer recurrence. Additionally, rucaparib is being studied for its potential use in treating other cancers, such as prostate and breast cancer, particularly in individuals with specific genetic mutations.