CDK12 and breast neoplasm: Moreover, overexpression of CDK12 promotes breast tumorigenesis by hyperactivating the serine-glycine-one-carbon network.417 Consequently, in vivo treatment of CDK12-overexpressing breast tumors with methotrexate chemotherapy yielded positive responses, underscoring the broader implications of CDK12 not only in DNA damage response mechanisms but also in metabolism.417