Valemetostat tosylate is primarily used in the treatment of certain types of cancers, particularly those involving hematologic malignancies. It functions as a dual inhibitor of the EZH2 and EZH1 enzymes, which play critical roles in the regulation of gene expression through histone methylation. By targeting EZH2 and EZH1, this compound helps to suppress the growth and proliferation of cancer cells that rely on this pathway for survival.

One of the key applications of valemetostat tosylate is in the treatment of relapsed or refractory adult T-cell leukemia/lymphoma (ATLL), a rare and aggressive form of non-Hodgkin lymphoma. It has shown promise in clinical trials for its ability to induce tumor regression and improve patient outcomes. Additionally, it is being investigated for its potential use in other cancers where EZH2 or EZH1 overexpression or mutations contribute to disease progression, such as certain subtypes of diffuse large B-cell lymphoma (DLBCL) and solid tumors.

The compound is administered orally, making it a convenient option for patients requiring long-term therapy. Its targeted mechanism of action offers a more precise approach to cancer treatment, potentially reducing the side effects associated with traditional chemotherapy. Ongoing research continues to explore its efficacy and safety in broader cancer indications, as well as its potential in combination therapies with other anticancer agents.