TLCD3A (also known as CT120) is a plasma membrane-associated protein localized to chromosome 17.3 that plays a critical role in lung carcinogenesis. The gene encodes a 257-amino acid protein with seven transmembrane domains and functions as a membrane-associated transporter involved in amino acid transport and glutathione metabolism 1. TLCD3A interacts with SLC3A2 and GGTL3B, suggesting roles in cellular nutrient homeostasis 1. Functionally, TLCD3A promotes cell proliferation through activation of Raf/MEK/Erk and PI3K/Akt signaling cascades 2. The gene is notably absent from normal lung tissue but highly expressed in lung cancer cell lines and primary lung tumors 34. TLCD3A overexpression enhances cell proliferation in vitro and tumorigenicity in vivo, while silencing reduces cyclin D1/Cdk4 expression and increases p53 and caspase-3, suppressing growth and sensitizing cells to apoptosis 54. An alternative splice variant, CT120B, exhibits antagonistic effects, inhibiting cell growth through delayed G1/S phase transition 6. Beyond lung cancer, TLCD3A was identified as a diagnostic biomarker in ulcerative colitis 7. These findings suggest TLCD3A as a potential therapeutic target for lung cancer treatment.