Prognostic significance of lymph node retrieval in localized rectal cancer (RC): A registry analysis of 8,964 patients (pts).

Abstract

3566 Background: In contrast to colon cancer, the prognostic implications of reduced lymph node retrieval in RC are unclear. We investigated the association between the total number of lymph nodes examined in early stage RC and disease specific survival (DSS) in two cohorts: 1) pts who underwent surgery and adjuvant (ADJ) chemoradiation (chemoXRT), and 2) those who received neoadjuvant (NEO) chemoXRT. Methods: Using the California Cancer Registry, we identified 8,946 pts with stage I – III RC diagnosed from 2000 to 2007. Of these, 4,790 underwent tri-modality therapy: 2,946 patients (61.5%) had NEO chemoXRT and 1,844 patients (38.5%) had ADJ chemoXRT. Multivariate Cox proportional hazards models were constructed for DSS, adjusting for age, sex, race, socioeconomic status, T-stage and lymph node number. DSS was compared between NEO and ADJ cohorts within separate subgroups of pathologic node positive and node negative RC. Results: Although there was no difference in overall DSS between the NEO and ADJ cohorts, the median number of lymph nodes examined was reduced in patients who had undergone NEO chemoXRT (8 vs. 11, p<0.0001). For all pts treated with tri-modality therapy, advancing age and higher T-stage were associated with significantly reduced DSS. Positive lymph nodes were associated with worse DSS regardless of the timing of therapy, although the effect was stronger for residual lymph nodes in the NEO cohort (HR 2.8 vs. 1.8 in ADJ cohort, p<0.001). For node negative pts in the ADJ cohort, increased lymph node retrieval was associated with improved DSS (HR per node 0.952, p=0.017); however, no association between lymph nodes examined and DSS was seen in the NEO cohort (p=0.282). Conclusions: Residual positive lymph nodes in pts treated with NEO chemoXRT are more strongly associated with poorer DSS than in pts treated with surgery and ADJ chemoXRT. NEO chemoXRT dissociates the connection between lymph node retrieval and survival in RC. This finding highlights a key difference between colon and RC and underscores the need for a different interpretation of the pathologic findings after NEO therapy.