Macroscopic and microscopic features indicating serosal invasion of colonic adenocarcinoma

Abstract

Objectives: Colonic adenocarcinoma poses a significant global health burden. Accurate detection of serosal invasion (pT4) is crucial for prognosis, yet inconsistent grossing protocols create diagnostic challenges. We aimed to evaluate macroscopic predictors of serosal invasion, determine the minimum tumor blocks required for accurate staging, and assess pT4 frequency at Siriraj Hospital. Materials and methods: We performed a retrospective review of a cohort comprising 218 patients diagnosed with colonic adenocarcinoma. The assessment was conducted by gastrointestinal pathologists and a trainee, integrating clinical records and macroscopic characteristics. Macroscopic features were categorized, including serosal surface appearance (smooth, irregular, bulging, perforated, adherent), tumor circumferential involvement, and depth of invasion on the cut surface (confined to muscularis propria, into pericolic tissue, or through serosa), correlated with histopathological evaluation according to the AJCC Cancer Staging Manual, 8th edition. Statistical analyses were executed to identify independent predictors of pT4a staging. Results: The pT4 prevalence was 20.2% (pT4a: 14.7%, pT4b: 5.5%). Multivariate analysis confirmed irregular serosa as a strong predictor (aOR: 7.03, 95% CI: 1.99–24.71). Notably, macroscopic observation of tumor penetration through the serosa on the cut surface exhibited the highest predictive value (aOR: 48.76, 95% CI: 9.43–252.15). Data indicated that submitting at least two blocks from the tumor-serosa interface ensured reliable staging. Conclusions: Our pT4 rates align with international benchmarks. Irregular serosa and macroscopic serosal penetration are robust pT4a predictors. We recommend meticulous gross examination and submitting a minimum of two blocks from the deepest invasion point to optimize staging accuracy.