Original ArticlesThe Width of Invasion in Malignant Melanoma Is a Novel Prognostic Feature That Accounts for Outcome Better Than Breslow ThicknessSaldanha, Gerald MBChB, MRCP (UK), FRCPath, PhD*,†; Khanna, Aarushi MSc‡; O’Riordan, Marie BA, MBChB, FRCPath†; Bamford, Mark MBChB, BSc, FRCPath, DipRCPath†Author Information *Leicester Cancer Research Centre ‡Leicester Medical School, University of Leicester †University Hospitals of Leicester NHS Trust, Leicester, UK Conflicts of Interest and Source of Funding: Supported by Small Grant S1212 from the British Skin Foundation (G.S.), a Small Research Grants Programme award from the Hope Foundation (G.S.), and Project Grant C12443/A18370 from Cancer Research UK (G.S.), and an Intercalated Studies student Grant from the Association of Clinical Pathologists (A.K.). The authors have disclosed that they have no significant relationships with, or financial interest in, any commercial companies pertaining to this article. Correspondence: Gerald Saldanha, MBChB, MRCP (UK), FRCPath, PhD, Leicester Cancer Research Centre, University of Leicester, Level 3 Sandringham Building, Leicester Royal Infirmary, Leicester LE1 5WW, UK (e-mail: [email protected]). The American Journal of Surgical Pathology: November 2020 - Volume 44 - Issue 11 - p 1522-1527 doi: 10.1097/PAS.0000000000001529 Buy SDC Metrics Abstract Breslow thickness (BT) is the cornerstone of malignant melanoma staging. However, to our knowledge no-one has ever assessed the horizontal width of invasion, measured microscopically, as a prognostic feature. This was investigated as a prognostic feature in this study. A retrospective cohort of 1329 melanoma cases was collected from patients presenting to a UK teaching hospital from January 1, 2004, to December 31, 2014. The main outcome was overall survival (OS). We found that width was associated with OS in multivariable analysis (hazard ratio=1.05, 95% confidence interval: 1.03-1.07, P<0.001) and was similarly significant for melanoma-specific survival and metastasis-free survival. Its presence rendered BT nonsignificant. The width was significantly associated with OS after adjustment for American Joint Committee on Cancer (AJCC), version 8 clinical tumor stage (hazard ratio=1.05, 95% confidence interval: 1.03-1.07, P<0.001), and bootstrap validation showed only slight model optimism. Similar associations were seen for melanoma-specific survival and metastasis-free survival. However, the combination of invasive width and BT did not account for the outcome as well as another novel histologic feature, tumor area, which was measured using the calculated tumor area method. In conclusion, this study is the first investigation of a novel histologic feature, invasive melanoma width, and demonstrates its strong independent association with outcome. Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.