Automated digital volume measurement of melanoma metastases in sentinel nodes predicts disease recurrence and survival

Aims: Total metastatic volume (TMV) is an important prognostic factor in melanoma sentinel lymph nodes (SLNs) that avoids both the interobserver variation and unidirectional upstaging seen when using semi-quantitative size estimates. However, it is somewhat laborious for routine application. Our aim was to investigate whether digital image analysis can estimate TMV accurately in melanoma SLNs. Methods and results: TMV was measured in 147 SLNs from 95 patients both manually and by automated digital image analysis. The results were compared by Bland-Altman plots (numerical data) and kappa statistics (categorical data). In addition, disease-free and melanoma-specific survivals were calculated. Mean metastatic volume per patient was 10.6 mm(3) (median 0.05 mm(3); range 0.0001-621.3 mm(3)) and 9.62 mm(3) (median 0.05 mm(3); range 0.00001-564.3 mm(3)) with manual and digital measurement, respectively. The Bland-Altman plot showed an even distribution of the differences, and the kappa statistic was 0.84. In multivariate analysis, both manual and digital metastasis volume measurements were independent progression markers when corrected for primary tumour thickness [manual: hazard ratio (HR): 1.21, 95% confidence interval (CI): 1.07-1.36, P = 0.002; digital: HR: 1.21, 95% CI: 1.06-1.37, P = 0.004]. Conclusions: Stereology-based, automated digital metastasis volume measurement in melanoma SLNs predicts adisease recurrence and survival.