Comparative analysis of tertiary lymphoid structures for predicting survival of colorectal cancer: a whole-slide images-based study.

Background: Tertiary lymphoid structures (TLS) are major components in the immune microenvironment, correlating with a favorable prognosis in colorectal cancer. However, the methods used to define and characterize TLS were not united, hindering its clinical application. This study aims to seek a more stable method to characterize TLS and clarify their prognostic value in larger multicenter cohorts.

Methods: A total of 1609 patients from four hospitals and The Cancer Genome Atlas database were analyzed. We quantified the number and maximum length of TLS along the invasive margin of tumor using hematoxylin and eosin-stained whole-slide images (WSIs). Additionally, the length of the invasive margin was determined to calculate the TLS density. The prognostic value of TLS for overall survival was evaluated. In addition, we examined the association between TLS density and immune cell infiltration using immunohistochemistry-stained WSIs. The performance for predicting overall survival was measured using hazard ratios (HR) with 95% confidence intervals (CI).

Results: Among the three TLS quantification methods, TLS density has the strongest discriminative performance. Survival analysis indicated that higher TLS density correlated with better overall survival [HR for high vs. low 0.57 (95% CI 0.42-0.78) in the primary cohort; 0.49 (0.35-0.69) in the validation cohort; 0.35 (0.18-0.67) in TCGA cohort]. A high TLS density was associated with a high level of CD3⁺ T cell infiltration.

Conclusions: Based on this comparative multicenter analysis, TLS density was identified as a simple, robust, and effective immune prognostic index for colorectal cancer.