009 Comparing the number needed to biopsy (NNB) ratio for melanoma diagnosis between teledermatology and face-to-face models of care

Abstract

The Elective Recovery Plan, published by NHS England (2022), has advocated that teledermatology (TD) should be available in every service receiving urgent suspected skin cancer referrals. However, evidence supporting the effectiveness of TD for the accurate diagnosis and triage of skin lesions remains limited. A 2018 Cochrane review found variable agreement between TD and face-to-face (FTF) assessment of lesions considered to be of low concern when seen FTF, with remote assessment more likely to recommend intervention (including excision) for low-risk lesions. The number needed to biopsy (NNB) ratio, calculated by dividing the total number of biopsies by the number of biopsied skin cancers, is increasingly used as a metric for the diagnostic accuracy for melanoma detection, with a low ratio suggesting high specificity and vice versa. We undertook a study to compare the NNB ratio for melanoma detection between TD and FTF models for assessing new 2-week-wait (2WW) skin cancer referrals within our service. Over 2019–2020, the service switched over from FTF to a full TD consultant-run model for 2WW referrals. Retrospective analysis of the FTF 2WW model between August and November 2018 identified 53 cases suspicious for melanoma referred for biopsy [30 women and 23 men; median age 44 years (range 27–90)]. Of these, six patients received a histopathological diagnosis of melanoma (NNB 8.8). Retrospective analysis of the TD model between August and November 2022 identified 62 cases suspicious for melanoma triaged directly to a biopsy appointment [37 women and 25 men; median age 49.5 years (range 18–90)]. Of these, three patients received a histopathological diagnosis of melanoma (NNB 20.7). NNB in the TD model was 2.3 times higher than in the FTF model. The NNB of 8.8 in our FTF 2WW model is comparable to a review of 46 studies, which generated an NNB of 7.5 for dermatologists worldwide. The higher NNB of 20.7 for TD indicates poorer diagnostic accuracy for melanoma in this model. The higher NNB in TD is consistent with previous findings that remote assessment is more likely to lead to the excision of low-risk lesions. Further large-scale studies are needed to compare NNB in teledermatology vs. FTF models of skin cancer assessment. TD brings considerable advantages of convenience and increased clinic capacity but may come at a cost of lower specificity for melanoma diagnosis and an increase in the number of biopsies of benign lesions.