Validation Of The Newly Proposed Who Classification System For Conjunctival Melanocytic Intraepithelial Lesions: A Comparison With The 'C-Min' And 'Pam' Classification Schemes.

Abstract Purpose To compare the sensitivity, specificity, accuracy, and inter-observer agreement of the two most commonly used classification systems for conjunctival melanocytic intraepithelial lesions with the new WHO classification. Design Retrospective case series and evaluation of classification systems. Methods Pathology and medical records of all patients, who underwent primary biopsy for conjunctival primary acquired melanosis (PAM) at Wills Eye Hospital between 1974 and 2002, with at least 36 months follow-up were reviewed. Data collected included age, sex, clinical findings, recurrence, and progression to melanoma. Twelve ophthalmic pathologists analyzed scanned hematoxylin-and-eosin stained virtual microscopic slides using three classification systems: PAM, conjunctival melanocytic intraepithelial neoplasia (C-MIN) and the World Health Organization (WHO) 4th edition classification of conjunctival melanocytic intraepithelial lesions (CMIL). Observer agreement, sensitivity, specificity, and diagnostic accuracy of each classification system were assessed. Results There were 64 patients who underwent 83 primary excisions with cryotherapy for conjunctival PAM, with adequate tissue for histopathologic evaluation. The inter-observer percent agreement in distinction between the low-grade and high-grade lesions was 76% for PAM, 67% for C-MIN, and 81% for WHO classification system. Low-grade lesions provided the greatest interpretative challenge with all three classification systems. The three classification systems had comparable accuracy of 81%-83% in their ability to identify lesions with potential for recurrence. Conclusions This study highlights the comparable strengths and limitations of the three classification systems for conjunctival melanocytic intraepithelial lesions and suggests that the simplified WHO classification scheme is appropriate for evaluation of these lesions.