Introduction. Protein O-glycosylation abnormalities are found in most carcinomas. Several clinically useful biomarkers detecting these changes have been developed. The initial step of synthesis of mucin-type O-glycans is catalyzed by a complex enzyme family (UDP-N-acetyl-D-galactosamine:polypeptide N-acetylgalactosaminyltransferases; GalNAc-Ts). We previously found that GalNAc-T13 isoenzyme is a strong predictor of poor clinical outcomes in neuroblastoma1 and breast cancer patients2. As shown in ISLB congress 2023, given that GalNAc-T13 is also expressed in non-small cell lung cancer (NSCLC)3, we evaluated GALNT13 expression in blood by nested RT-PCR in 119 NSCLC patients from Maciel Hospital, Montevideo, finding a possible correlation with clinical outcomes. In this work, we quantified GALNT13 expression by RT-Digital-PCR in serial samples of peripheral blood of NSCLC patients, to evaluate GALNT13 as a new potential liquid biopsy follow-up biomarker. Methods. GALNT13 expression was evaluated by an RT-Digital-PCR method (QIAcuity, Qiagen®) in peripheral blood of 39 NSCLC patients and 48 normal donors from Maciel Hospital, Montevideo. Results were correlated with clinical-pathologic data, treatment response and patients’ survival. Results. Cut-off was defined by analyzing GALNT13 expression in 48 healthy individuals. 39 NSCLC patients with 1-9 follow-up samples were studied. The median age was 64 years old (ranging from 44 to 78); 56.4% corresponded to males and 43.6% to females. GALNT13 expression was detected in 64% of NSCLC patients. Concerning histological types, GALNT13 expression was detected in 56% of adenocarcinoma patients, 75% of squamous cell carcinoma patients, and 83% of other histologic types. Relating to stages, the enzyme was found in 28.6% of stage I/II patients, 73.3% of stage III, and 73.7% of stage IV patients. GALNT13 expression in the initial samples was significantly correlated with clinical outcomes. When analyzing serial samples, we noticed that in those patients in remission, the expression of the enzyme decreased significantly. In contrast, patients experiencing disease progression showed elevated GALNT13 expression, sometimes even prior to imaging detection. Conclusion. In this study, we suggest that monitoring GALNT13 expression in blood of non–small cell lung cancer by digital RT-PCR could be a potential new follow-up biomarker in liquid biopsy for lung cancer patients.