Impact of microscopic extranodal tumor deposits on the outcome of patients with rectal cancer

Abstract

Purpose: Microscopic mesorectal soft tissue extranodal deposits discontinuous with the primary tumor are identified in many rectal adenocarcinomas. Current guidelines consider them to be involved lymph nodes. We studied the impact of these deposits on the outcome of patients with rectal cancer.

Methods: This was a retrospective study, in which histology slides were reviewed from 55 patients whose resection specimens for rectal cancer were staged as Dukes C or Dukes B with extranodal deposits. Twenty-nine patients had extranodal deposits (19 males), and 26 control patients had lymph node involvement only (14 males). Patient outcome was analyzed in terms of local and systemic control and survival.

Results: Distant metastases were diagnosed earlier in patients with extranodal deposits (mean, 14 months) compared with controls (mean, 37 months; P = 0.001). On follow-up, 31.03 percent (9/29) from the extranodal deposit group developed liver metastases compared with 11.5 percent (3/26) of the control group (P = 0.08). Local recurrence was seen in 17.2 percent of patients from the extranodal deposit group and 3.8 percent of the control group (P = not significant). Cancer-related mortality was higher in the extranodal deposit group (16 vs. 7 patients; P = 0.09). The three-year actuarial survival was 48.27 percent in patients with extranodal deposits and 65.38 percent in those without. A significant association was noted between the number of extranodal deposits and intramural vascular invasion (P = 0.017), extramural vascular invasion (P = 0.039), perineural invasion (P = 0.039), and lymph node involvement (P = 0.008).

Conclusion: These data suggest that extranodal deposit is a distinct form of metastatic disease in patients with rectal cancer. The association with vascular invasion and earlier development of metastases probably infers that a significant proportion of extranodal deposits may represent blood-borne spread. These tumor foci should be considered as indicators of poor prognosis.