{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,3]],"date-time":"2026-09-03T12:03:22Z","timestamp":1788437002479,"version":"build-2803163510"},"reference-count":34,"publisher":"MDPI AG","issue":"10","license":[{"start":{"date-parts":[[2026,5,21]],"date-time":"2026-05-21T00:00:00Z","timestamp":1779321600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Cancers"],"abstract":"<jats:p>Background\/Objectives: Body-surface-area-based dosing of continuous-infusion 5-fluorouracil does not account for inter-individual pharmacokinetic variability. This pilot study explored whether patient-level representative plasma 5-fluorouracil exposure within the target area under the concentration\u2013time curve (AUC) range was associated with clinical outcomes. It evaluated a prototype immunochromatographic assay as a preliminary monitoring tool. Methods: Fifteen patients with unresectable advanced or recurrent colorectal cancer who received continuous-infusion 5-fluorouracil-based chemotherapy were prospectively evaluated between 1 January 2017 and 30 April 2018. Plasma 5-fluorouracil levels were measured during eight treatment cycles at three time points in each cycle. Representative AUC values were calculated using median concentrations across cycles and interpreted as exploratory patient-level exposure indices. Tumor response, grade \u22652 adverse events, progression-free survival, and overall survival were assessed descriptively. Results: The median representative AUC was 24.3 mg\u00b7h\/L. Eight patients (53.3%) were within the target range of 20\u201330 mg\u00b7h\/L, whereas seven (46.7%) were outside it. Disease control was observed in 7 of 8 patients (87.5%) within the target range and in 3 of 7 patients (42.9%) outside it. Grade \u22652 adverse events were less frequent in the target-range group (2\/8, 25.0%) than in the outside-range group (6\/7, 85.7%; p = 0.041). Progression-free survival was numerically longer in the target-range group (17.2 vs. 9.2 months, p = 0.36), while overall survival did not differ clearly (p = 0.76); these survival analyses were exploratory. The prototype immunochromatographic assay showed a favorable correlation with the My-5FU assay (R2 = 0.762), but Bland\u2013Altman analysis showed relatively wide limits of agreement. Conclusions: Target plasma 5-fluorouracil exposure was associated with lower clinically relevant toxicity and may support favorable tumor control in this pilot cohort. The prototype immunochromatographic method demonstrated preliminary feasibility for rapid plasma 5-FU monitoring but requires further validation before routine dose adjustment.<\/jats:p>","DOI":"10.3390\/cancers18101673","type":"journal-article","created":{"date-parts":[[2026,5,21]],"date-time":"2026-05-21T15:02:27Z","timestamp":1779375747000},"page":"1673","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Plasma 5-Fluorouracil Exposure, Clinical Outcomes, and Therapeutic Drug Monitoring in Advanced Colorectal Cancer"],"prefix":"10.3390","volume":"18","author":[{"given":"Naoki","family":"Sakuyama","sequence":"first","affiliation":[{"name":"Department of Surgery, The Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kiichi","family":"Nagayasu","sequence":"additional","affiliation":[{"name":"Department of Surgery, Tokyo Metropolitan Tobu Chiiki Hospital, Tokyo 125-8512, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yu","family":"Abe","sequence":"additional","affiliation":[{"name":"Department of Surgery, Tokyo Metropolitan Tobu Chiiki Hospital, Tokyo 125-8512, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Takumi","family":"Ochiai","sequence":"additional","affiliation":[{"name":"Misato Care Center, Aiyukai Medical Corporation, Misato 341-0028, Saitama, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Futoshi","family":"Shibasaki","sequence":"additional","affiliation":[{"name":"Molecular Medical Research Project, Department of Genome Medicine, Tokyo Metropolitan Institute of Medical Science, 2-1-6 Kamikitazawa, Setagaya-ku, Tokyo 156-8506, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,5,21]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"352","DOI":"10.1007\/BF02897292","article-title":"Clinical significance of monitoring serum levels of 5-fluorouracil by continuous infusion in patients with advanced colonic cancer","volume":"26","author":"Yoshida","year":"1990","journal-title":"Cancer Chemother. 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