Patent blue staining as a method to improve lymph node detection in rectal cancer following neoadjuvant treatment.

Lymph node involvement is one of the most important prognostic factors in rectal cancer. After neoadjuvant treatment the number of retrieved lymph nodes is often reported to be low which impairs reliable tumour staging. This study examines the effect of patent blue staining on the number of harvested lymph nodes and evaluates whether a higher number of retrieved lymph nodes is of prognostic significance. Between March 2007 and December 2010, 295 consecutive patients with locally advanced rectal cancer following neoadjuvant treatment were included. Specimens were either not stained (NB), injected with patent blue into the mesorectum (MB) or directly into the inferior mesenteric artery (AB). Data were retrieved from a prospective database. The number of evaluated lymph nodes was significantly higher in the stained specimens: mean 6.8 in the NB group (n=89), 11.5 in the MB group (n=86) and 17.4 in the AB group (n=106) (p<0.001). The percentage of patients with a minimum of 12 lymph nodes increased from 15.5% (NB) to 44.2% (MB) to 74.5% (AB) (p<0.001). The three-year cancer specific survival for the lymph node ratio (LNR) was 95% (0), 94.4% (0.01-0.1), 80.1% (0.11-0.4) and 63.7% (0.41-1). The use of patent blue in patients who underwent rectal cancer surgery after neoadjuvant treatment significantly enhanced lymph node harvest. Injection into the inferior mesenteric artery was most effective. This relatively simple and generally applicable method can help to improve lymph node detection which lowers the LNR and allows adequate tumour staging.