Nodal distribution, stage migration due to diameter measurement and the prognostic significance of metastasis volume in melanoma sentinel lymph nodes: a validation study

To validate metastasis location, maximum metastasis diameter ( MMD ) measurement induced stage migration and the prognostic significance of total metastatic volume ( TMV ) in melanoma sentinel lymph nodes ( SLN s). A new 227 patient SLN cohort examined by complete step sectioning (250 μm) was tested for TMV and MMD prognostic significance; metastasis location by three different three‐level protocols ( Central vs Peripheral vs Global ); and potential treatment changing down‐staging by two restricted five‐level protocols [ Reduced Central (250 μm) vs Reduced Even (500 μm) sections]. Both TMV and MMD independently predicted recurrence ( TMV , hazard ratio ( HR ): 1.21; 95% confidence interval ( CI ) 1.07–1.37; p = 0.003; and MMD , HR : 1.46; 95% CI 1.08–1.98, p = 0.02) and melanoma‐specific death ( TMV , HR : 1.30; 95% CI 1.11–1.51; p = 0.001; and MMD , HR : 1.82; 95% CI 1.25–2.66, p = 0.002). The Central , Peripheral and Global protocols detected 72%, 76% and 83% of metastases found by complete step sectioning. Based on MMD , using the Reduced Central or Reduced Even protocols, potential treatment changing down‐staging occurred in 20 (20%) or 13 (13%) of SLN ‐positive patients. This validation study establishes that: (i) metastases are globally located in melanoma SLN s; (ii) MMD but not TMV leads to uni‐directional stage migration; and (iii) TMV analysis is of prognostic significance.