Pericolonic tumor deposits in patients with T3N+MO colon adenocarcinomas: markers of reduced disease free survival and intra-abdominal metastases and their implications for TNM classification.

BACKGROUND: A pericolonic tumor deposit (PTD) is a grossly palpated adenocarcinomas within pericolonic adipose tissue not within a lymph node. The source and prognostic significance of PTDs has not been well defined.
METHODS: The authors studied 418 T3N+M0 colon adenocarcinomas to determine the frequency and significance of PTDs. They also step-sectioned 30 PTDs to determine their origin and assist in their optimum TNM classification.
RESULTS: Seventy-one (18%) of 400 consecutively examined cases had PTDs. The actuarial 1-, 2-, and 5-year disease free survival rates were significantly lower among patients with a PTD. PTDs, regardless of size, significantly impacted disease free survival. Increasing numbers of PTDs was associated with shorter disease free survival. Adenocarcinoma grade, a PTD, increasing numbers of PTDs, and number of lymph node metastases were independently associated with shorter disease free survival. The likelihood of extrahepatic abdominal failure was proportionally greater with increasing numbers of PTDs. Adenocarcinoma was observed in perineural, peri-large vessel, or intravascular locations in step-sectioned PTDs.
CONCLUSIONS: A PTD is a perineural, perivascular, or intravascular tumor extension beyond the muscularis propria. They are distinct from lymph node metastases and should not be considered their prognostic equivalent. The disease free survival impact of even small PTDs was significant, suggesting that PTDs of all sizes should be considered a single entity. TNM classification of PTDs as lymph node metastases or discontinuous tumor extension is probably not accurate. The number and greatest dimension of PTDs should be reported separately from lymph node metastases.