The American Joint Committee on Cancer's Cancer Staging Manual 7th edition defines pericolonic tumor deposits (TDs) as discrete tumor foci in pericolic fat showing no evidence of residual lymph node (LN). This definition relies on subjective features rather than size (5th edition) or shape (6th edition) and introduced the category N1c. Although typically straightforward, metastases are encountered for which the distinction between LNs and TDs is unclear. For data to be meaningful, agreement on distinguishing features between positive LNs and TDs is needed.
To assess agreement among gastrointestinal pathologists evaluating difficult metastases and to report the distinguishing features they found helpful.
Twenty-five tumor metastases from right-sided colonic adenocarcinomas were selected in which the distinction between positive LNs and TDs was challenging. Virtual slides were reviewed by 7 gastrointestinal pathologists. A list of features potentially helpful in differentiating positive LNs and TDs was ranked for usefulness by each pathologist. Every metastasis was diagnosed as positive LN or TD. For each case diagnosed as positive LN, reviewers were asked to list every feature used in diagnosis.
Complete agreement was found for 11 of 25 metastases, 5 positive LNs and 6 TDs (κ statistic, 0.48; 95% confidence interval, 0.28-0.67). Top-ranked features included round shape, peripheral lymphocyte rim, peripheral lymphoid follicles, possible subcapsular sinus, residual LN in surrounding fibroadipose tissue, and thick capsule. The top used features were similar among reviewers.
Significant agreement on positive LNs and TDs in difficult colonic adenocarcinoma metastases was found among evaluators, but inconsistency remains. Round shape, peripheral lymphocyte rim, peripheral lymphoid follicles, possible subcapsular sinus, residual LN in surrounding fibroadipose tissue, and thick capsule were most often used to aid in diagnosis.