# Limited prognostic value of revised tumour deposit definition in tumour node metastasis (TNM)8 in colorectal cancer: national cohort study

## TL;DR

A national study found that the revised definition of tumour deposits in TNM8 did not improve prognosis for colorectal cancer patients compared to the older TNM7 definition.

## Contribution

The study demonstrates that the stricter TNM8 tumour deposit definition lacks improved prognostic value over TNM7.

## Key findings

- The TNM8 tumour deposit definition showed improved distant metastasis-free survival but not overall survival.
- No significant prognostic difference was found between TNM7 and TNM8 tumour deposit classifications.
- The revised TNM8 definition increased complexity without enhancing clinical utility.

## Abstract

Tumour deposits are an important prognostic factor in colorectal cancer. In tumour node metastasis (TNM)8, the definition became stricter as TNM7’s previous requirement for absence of lymphatic tissue was expanded to also include nerve and vascular tissue. TNM8 has been criticised for its limited prognostic value. This study aimed to compare prognostic differences for patients with colorectal cancer with tumour deposits staged with TNM7 and TNM8.

This national retrospective cohort study included patients with colorectal cancer who underwent surgical resection in 2011–2014 and 2017–2019. Exclusion criteria were metastatic stage IV disease, non-radical or non-curative surgery, unstated tumour deposit status, or early (≤ 30 days) mortality. Univariable, multivariable, and interaction term Cox regression analyses examined differences in overall survival and distant metastasis between TNM7 and TNM8 stagings. Multivariable models were adjusted for age, gender, American Society of Anesthesiologists score, number of positive lymph nodes, TNM stage, neoadjuvant, and adjuvant treatment.

Of 19 413 patients operated on during 2011–2014 and 15 027 during 2017–2019, 23 966 were included. The TNM7 cohort had 1225 (9.5%) patients with tumour deposits, and the TNM8 cohort had 1407 (12.7%). There was an improved 5-year distant metastasis-free survival for patients with tumour deposits (hazard ratio 2.35 (95% confidence interval 2.14 to 2.58)) in the TNM8 cohort, but no benefit in overall survival, compared with patients in the TNM7 cohort. Interaction analysis revealed no prognostic difference associated with tumour deposit status between the two TNM editions.

Despite increased complexity, the revised definition of tumour deposits in TNM8 did not enhance prognostic ability compared with TNM7.

This national retrospective cohort study highlights that TNM8’s new definition of tumour deposits has added increased complexity and reduced reproducibility without enhancing prognostic ability compared with TNM7. The definition requires further refinements in future TNM editions.