Lymph node ratio for gastric cancer: useful instrument or just an expedient to retrieve fewer lymph nodes?
Ann Surg. 2014 Apr;259(4):e65.
We read with great interest the article by Wang et al,1 who studied 18,043 patients with gastric cancer who underwent gastrectomy, identified from the US Surveillance, Epidemiology, and End Results (SEER) database. Among them, 7233 patients were used in a training set divided into 5 node ratio (Nr) groups and a TNrM staging system was constructed. Median survival and overall survival, based on the seventh edition of AJCC2 and TNrM staging systems, were compared, and the analysis was repeated in a validation set of 10,810 patients. Misclassification was defined by the authors if the median survival for patients in any subgroup fell out of the 95% confidence interval of the overall group’s median survival.
Comparing the seventh edition of AJCC staging system and the newly developed TNrM staging system, Wang et al demonstrated that the former misclassified 57% of patients and the latter misclassified only 12%. The most important contribution that this article gave to the scientific community is probably the official validation, with a staging system, of the concept of lymph Nr for gastric cancer.
The ratio between positive and examined lymph nodes has been proposed as a simple, convenient, and reproducible system that can be used to better identify subgroup of patients with gastric, breast, and colon cancer with similar prognosis, thus minimizing the “stage migration” phenomenon that can be observed using the current TNM staging system.
During the last decade, several studies evaluated the prognostic impact of the ratio between the number of positive nodes and analyzed nodes (Nr) in gastric cancer and up until now all supported the simplicity, reproducibility, and value of this staging system. The main advantages of the Nr are that it is much less influenced by the extent of lymphadenectomy and that the ‘‘stage migration’’ phenomenon is rarely observed when this classification is adopted. This was also stated to occur when the number of retrieved lymph nodes was fewer than 15. Nonetheless, the vast majority of these studies were carried out in specialized centers where an extended lymphadenectomy was usually performed.
As a consequence, a high number of retrieved lymph nodeswere normally reported and cases with fewer than 15 nodes examined were frequently excluded.
We would like to stress just a few considerations that the authors have brilliantly exposed in their conclusions to stimulate the discussion on this interesting topic. In the study by Wang et al, only 31% of patients in the training data set and 34% in the validation data set had more than 15 lymph nodes examined, according to AJCC recommendations.
The TNrM staging system should be considered as an optimal instrument for medical oncologists to better stratify patientswith limited lymph node dissection and identify those who may benefit from adjuvant therapies.
But, in our opinion, the problem is not that the seventh edition of AJCC staging system overestimates survival. The real issue is whether surgical oncologists start considering the TNrM staging system as a “parachute” in case of inadequate node dissection, because inadequate lymph node dissection means inadequate surgery and inadequate surgery means inadequate cure and consequently a worse survival. The TNrM staging system could be introduced in clinical practice with optimal results without forgetting the basic rules of an adequate surgery.