Eur Radiol. 2026 Mar 15. doi: 10.1007/s00330-026-12466-y. Online ahead of print.
ABSTRACT
OBJECTIVES: To determine if the apparent diffusion coefficient (ADC) can distinguish acellular mucin from cellular mucin in the treated tumor bed of patients with mucinous rectal adenocarcinoma after neoadjuvant therapy.
MATERIALS AND METHODS: This retrospective study included patients with mucinous rectal adenocarcinoma treated with neoadjuvant therapy, followed by restaging MRI and surgical resection or biopsy. Three radiologists blinded to histopathology results independently segmented volumes of interest on diffusion-weighted imaging and ADC maps. A medical physicist performed histogram analysis of ADC map segmentations, calculating various ADC metrics: mean, standard deviation, median, 1st quartile, 2nd quartile, 3rd quartile, and 4th quartile. The Wilcoxon rank sum test with false discovery rate correction for multiple testing was used to examine associations between ADC metrics and tumor mucin cellularity at histopathology for each reader. Multivariable logistic regression was used to adjust for acquisition parameters and institutions.
RESULTS: Of 150 patients (mean age, 58 ± 14 years; 48/150 (32% female), 25 patients (17%) had acellular mucin and 125 (83%) had cellular mucin at histopathology. At univariable analysis, there was no significant association between any ADC metric and tumor mucin cellularity (q-value = 0.14-0.58). At multivariable analysis, most ADC metrics were significantly associated with tumor mucin cellularity for all readers (q-values = 0.016-0.025) with odds ratios between 0.09 (95% CI: 0.02, 0.42) and 0.49 (95% CI: 0.22, 0.96).
CONCLUSIONS: ADC may be a potential tool for assessing pathologic complete response in mucinous rectal adenocarcinoma after neoadjuvant treatment, after adjusting for acquisition parameters and institutions.
KEY POINTS: QuestionCan the apparent diffusion coefficient (ADC) distinguish between cellular and acellular mucin (i.e., pathologic complete response) in mucinous rectal adenocarcinoma after neoadjuvant therapy? FindingsAfter controlling for acquisition parameters, ADC metrics were significantly associated with tumor mucin cellularity. Clinical relevanceAcellular mucin is equivalent to clinical complete response and can undergo watch-and-wait management, whereas cellular mucin is incomplete response, and its safety for watch-and-wait management is not validated. ADC may be a potential tool to make the distinction to assist treatment decision-making.
PMID:41832931 | DOI:10.1007/s00330-026-12466-y
