Concordance and Reproducibility of Melanoma Staging According to the 7th vs 8th Edition of the AJCC Cancer Staging Manual

Joann G Elmore,Gary M Longton,Michael W Piepkorn,Heidi D Nelson,Raymond L Barnhill,Linda J Titus,Margaret S Pepe,Andrea C Radick,David E Elder,Martin A Weinstock,Stevan R Knezevich,Lisa M Reisch

doi:10.1001/jamanetworkopen.2018.0083

Abstract

The recently updated American Joint Committee on Cancer (AJCC) classification of cancer staging, the AJCC Cancer Staging Manual, 8th edition (AJCC 8), includes revisions to definitions of T1a vs T1b or greater. The Melanoma Pathology Study database affords a comparison,of pathologists' concordance and reproducibility in the microstaging of melanoma according to both the existing 7th edition (AJCC 7) and the new AJCC 8. To compare AJCC 7 and AJCC 8 to examine whether changes to the definitions of T1a and T1b or greater are associated with changes in concordance and reproducibility. In this diagnostic study conducted as part of the national Melanoma Pathology Study across US states, 187 pathologists interpreting melanocytic skin lesions in practice completed 4342 independent case interpretations of 116 invasive melanoma cases. A consensus reference diagnosis and participating pathologists' interpretations were classified into the Melanocytic Pathology Assessment Tool and Hierarchy for Diagnosis class IV (T1a) or class V ( T1b) using both the AJCC 7 and AJCC 8 criteria. Concordance with consensus reference diagnosis, interobserver reproducibility, and intraobserver reproducibility. For T1a diagnoses, participating pathologists' concordance with the consensus reference diagnosis increased from 44% (95% CI, 41%-48%) to 54% (95% CI, 51%-57%) using AJCC 7 and AJCC 8 criteria, respectively. The concordance for cases of T1b or greater increased from 72% (95% CI, 69%-75%) to 78% (95% CI, 75%-80%). Intraobserver reproducibility of diagnoses also improved, increasing from 59% (95% CI, 56%-63%) to 64% (95% CI, 62%-67%) for T1a invasive melanoma, and from 74% (95% CI, 71%-76%) to 77% (95% CI, 74%-79%) for T1b or greater invasive melanoma cases. Melanoma staging in AJCC 8 shows greater reproducibility and higher concordance with a reference standard. Improved classification of invasive melanoma can be expected after implementation of AJCC 8, suggesting a positive impact on patients. However, despite improvement, concordance and reproducibility remain low.

Highlights

Disease subclassification according to the AJCC Cancer Staging Manual by the American Joint Committee on Cancer (AJCC) is the customary and prevalent mode for stratifying patients with melanoma to estimate prognosis, determine appropriate surgical intervention, and assess eligibility for adjuvant therapies and clinical trials
Intraobserver reproducibility of diagnoses improved, increasing from 59% to 64% for T1a invasive melanoma, and from 74% to 77% for T1b or greater invasive melanoma cases
Improved classification of invasive melanoma can be expected after implementation of AJCC 8, suggesting a positive impact on patients

Summary

Introduction

Disease subclassification according to the AJCC Cancer Staging Manual by the American Joint Committee on Cancer (AJCC) is the customary and prevalent mode for stratifying patients with melanoma to estimate prognosis, determine appropriate surgical intervention, and assess eligibility for adjuvant therapies and clinical trials. The process presupposes that pathologists’ application of the AJCC histopathological criteria to individual cases of melanoma is accurate and reproducible. In the field of melanoma, there are only limited analyses quantifying the degree of reproducibility of AJCC microstaging between pathology observers.[1] Extensive variability has been noted among pathologists in the diagnosis of invasive melanoma.[2,3,4,5,6,7] One of the largest studies,[2] our previously published Melanoma Pathology Study (M-Path) of 187 US pathologists, found less than 50% agreement between pathologists and a consensus-derived reference diagnosis of T1a invasive melanoma, with improvement to 72% concordance for invasive melanoma T1b or greater. M-Path findings revealed only 46% interobserver agreement for T1a invasive melanoma, and 77% agreement for T1b or greater melanomas.[2]

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