Tazemetostat hydrobromide is primarily used in the treatment of certain types of cancer. It is specifically indicated for patients with metastatic or locally advanced epithelioid sarcoma who are not eligible for complete surgical removal. The drug works by inhibiting the EZH2 enzyme, which is often overactive in these cancers, thereby helping to slow down or stop the growth of cancer cells. Additionally, it has shown promise in treating follicular lymphoma, particularly in cases where the cancer has returned or is resistant to other treatments. By targeting the EZH2 mutation, it provides a therapeutic option for patients with limited alternatives. The application of this drug is typically determined by genetic testing to confirm the presence of EZH2 mutations, ensuring that it is used in patients who are most likely to benefit from its mechanism of action. Its use is closely monitored due to potential side effects, and it is often administered under the guidance of a healthcare professional experienced in cancer treatment.