The prognostic value of lymph node ratio after neoadjuvant chemoradiation and rectal cancer surgery.

BACKGROUND

Neoadjuvant chemotherapy decreases total lymph nodes harvested and possibly affects lymph node staging after total mesorectal excision in patients with rectal cancer.

OBJECTIVE

This study aimed to compare staging by lymph node ratio with staging by absolute number of positive lymph nodes.

DESIGN

This study is a retrospective cohort review.

SETTING

: A tertiary care referral center was the setting for this investigation.

PATIENTS

A total of 281 consecutive patients who underwent neoadjuvant chemoradiation and total mesorectal excision after histologically confirmed rectal cancer between January 1, 1998 and December 31, 2008 were included in this study.

MAIN OUTCOME MEASURES

Lymph node ratio is the number of positive lymph nodes divided by the total number of lymph nodes within one sample. Risk categories of low (0 to < 0.09); medium (0.09 to < 0.36); and high (≥ 0.36) for lymph node ratio were chosen by significance with the use of Cox proportional hazards models. These categories were then used in a reclassification table and compared with positive lymph node stage: low (0 positive nodes), medium (1-3 nodes), and high (> 3) by 5-year mortality rates.

RESULTS

The majority (87%) of patients were concordant in risk assessment. Thirty patients were downstaged to lower risk lymph node ratio categories without showing actual lower mortality rates. Seven patients were upstaged to a high-risk lymph node ratio category with a supporting higher 5-year mortality rate. When limiting the analysis to those with fewer than 12 nodes, 136 (95%) patients were concordant in risk assessment; all 30 incorrectly downstaged patients were removed, but the 7 correctly upstaged patients remained.

CONCLUSIONS

Patients who undergo neoadjuvant chemoradiation before rectal cancer surgery frequently have fewer than 12 lymph nodes harvested despite maintaining vigorous surgical standards. Lymph node ratios may provide excellent prognostic value and are possibly a better independent staging method than absolute positive lymph node counts when less than 12 lymph nodes are harvested after neoadjuvant treatment.