Early kinetics of CA19-9 and CEA after 5-FU-based chemotherapy for gastrointestinal cancers

INTRODUCTION: In gastrointestinal oncology, serum tumor markers such as CEA and CA19-9 are typically monitored over several weeks to assess therapeutic efficacy. The immediate impact of cytotoxic therapy on these serum tumor markers, however, remains poorly characterized. METHODS: We analyzed a single-center cohort of patients with advanced gastrointestinal cancers (pancreatic, biliary, colorectal, and esophageal) treated with 5-fluorouracil-based regimens. Paired serum samples were collected immediately before the start of chemotherapy (0 h) and at the removal of the 48-h 5-FU continuous pump (48 h). The primary endpoint was the percentage change of tumor markers during this time window (∆CEA and ∆CA19-9). Secondary endpoints included the association of these acute kinetics with subsequent radiographic response. RESULTS: 78 cycles of 5-FU-based chemotherapy were included (33 patients, median cycles per patient: 2). CA19-9 increased significantly after chemotherapy (median ∆CA19-9 + 4.8% per patient, Wilcoxon p = 0.015; mixed model p = 0.062; cycle-level range - 11% to + 92%), as did LDH (median ∆LDH + 12.8% per patient, both Wilcoxon and mixed model p < 0.001; cycle-level range - 39% to + 72%). CEA levels remained stable (median ∆CEA - 3.6% per patient, Wilcoxon p = 0.09; mixed model p = 0.05; cycle-level range - 20% to + 22%). There was no statistically significant association between early changes in serum tumor markers and radiographic outcome. DISCUSSION: In this hypothesis-generating study, 5-FU-based therapy leads to a statistically significant increase in CA19-9 and LDH levels, but not in CEA, after 48 h. The magnitude of the increase did not predict radiographic response.