PTC299 + letrozole

PTC299 + letrozole is a combination therapy consisting of **PTC299**, a novel oral small molecule inhibitor of dihydroorotate dehydrogenase (DHODH), and **letrozole**, an oral aromatase inhibitor used primarily as adjuvant therapy for estrogen receptor (ER)-positive breast cancer. PTC299 inhibits de novo pyrimidine synthesis and reduces vascular endothelial growth factor A (VEGFA) production by blocking DHODH, thereby suppressing tumor cell proliferation and angiogenesis[4]. Letrozole acts by inhibiting aromatase, blocking estrogen biosynthesis, and is highly effective in hormone receptor–positive breast cancer management[5]. The combination of PTC299 and letrozole is not an established or approved therapeutic regimen as of 2025, and there is no publicly available clinical evidence or development record explicitly describing this specific combination in oncology or other diseases. PTC299 has been evaluated for hematologic malignancies and solid tumors, while letrozole is a standard component of hormonal breast cancer therapies.