Validation of a nomogram predicting sentinel lymph node status in melanoma in an Irish population

Abstract

Background: Sentinel lymph node (SLN) positivity is an important prognostic factor in cutaneous melanoma. A nomogram has been developed at Memorial Sloan-Kettering Cancer Centre (MSKCC) to predict SLN positivity and this may be useful to select patients for SLN biopsy.

Aims: We aimed to determine whether this nomogram would be of clinical use in an Irish population.

Methods: Age, Breslow thickness, Clark's level, presence of ulceration and tumour location indices were used to calculate the probability of SLN positivity with the MSKCC nomogram in 124 patients who underwent SLN biopsy in Beaumont Hospital between 2006 and 2012. Discrimination and calibration of the nomogram were evaluated. Negative predictive value (NPV) of the nomogram was calculated, using a cut-off of nomogram predicted probability of <9%.

Results: SLN biopsy was positive in 25 patients (20.16%). Overall predictive accuracy of the nomogram was found to be significant with an area under the curve of 0.805 (95% confidence interval 0.710-0.899). The mean predicted probability correlated well with observed risk (r = 0.887). The NPV was 92.86% with an error rate of 3.23%. This would lead to a reduction in SLN biopsy rate of 45.16%.

Conclusions: This nomogram is valid and accurate at predicting SLN positivity in an Irish population. This may facilitate the clinical decision to perform a SLN biopsy in malignant melanoma.

Keywords: Irish/Ireland; Melanoma; Nomogram; Predictive value of tests; ROC curve; Sentinel lymph node biopsy.