Concordance and Reproducibility of Melanoma Staging According to the 7th vs 8th Edition of the <i>AJCC Cancer Staging Manual</i>.

Abstract

The recently updated American Joint Committee on Cancer (AJCC) classification of cancer staging, the <i>AJCC Cancer Staging Manual</i>, 8th edition (<i>AJCC 8</i>), 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 <i>(AJCC 7</i>) and the new <i>AJCC 8</i>. To compare <i>AJCC 7</i> and <i>AJCC 8</i> 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 <i>AJCC 7</i> and <i>AJCC 8</i> 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 <i>AJCC 7</i> and <i>AJCC 8</i> 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 <i>AJCC 8</i> shows greater reproducibility and higher concordance with a reference standard. Improved classification of invasive melanoma can be expected after implementation of <i>AJCC 8</i>, suggesting a positive impact on patients. However, despite improvement, concordance and reproducibility remain low.