Neck dissection in addition to surgery of the primary site is commonly recommended in head and neck cancer treatment. However, there has been no consensus on the number of nodes that need to be removed to constitute a sufficient neck dissection. Lymph node yield (LNY) relates to the number of nodes removed. Lymph node density (LND) is the ratio of positive nodes to LNY. The authors aimed to find out the prognostic value of LNY and LND by summarising and meta-analysing available literature. Out of 350 articles, 23 were included in the final synthesis.
Increased LNY was associated with better survival (hazard ratio 0.833; 95% CI 1.637-2.241). Increased LND was associated with poorer survival (hazard ration 1.916; 95% CI 1.637-2.241). They conclude that LNY can be used as a quality metric for neck dissections but due to limitations, should be adjusted for patient and disease factors, and that pathological procedures be standardised. Individual patient factors like age, weight, tumour size, grade, staging, anatomic location, and previous radiation influence LNY.
Furthermore, the number of nodes identified by pathology differs between pathologists, laboratories and pathology training levels. There remains a discrepancy of what constitutes an adequate LNY value. Most studies have used a cut-off of 18, used in one of the earliest studies by Ebrahimi et al, as he found that individuals with a yield of 1-17 had the poorest outcomes while those above 18 had similar outcomes. LND may help improve the risk-stratification of patients when used in conjunction with AJCC TNM staging post surgery. Because LNY is a denominator in calculating LND, they share common limitations. LND may not be an accurate representation of nodal density in the neck as LNY can be variable depending on the surgery. Cut-off values for high versus low LND varied from 1 to 20%. The most robust study settled on a cut-off of 7%.