Size Overlap Between Benign Melanocytic Choroidal Nevi and Choroidal Malignant Melanomas

¹ Ophthalmology, University of Cincinnati, Cincinnati, Ohio, United States
² Ophthalmology, University of Cincinnati, 260 Stetson Building, Suite 5300, Cincinnati, Ohio, 45267-0527, United States

^* To whom correspondence should be addressed. E-mail: correazm{at}uc.edu.

	Abstract

Purpose: To estimate size overlap between large choroidal nevi and small choroidal melanomas using plotted frequency distributions of tumor size. Methods: Frequency distributions of largest linear basal diameter (LBD) and thickness (TH) of choroidal nevi and melanomas were plotted from published data and cases in senior author’s private practice. Relative frequencies of choroidal nevi and melanomas were estimated from published data. Relative frequency distributions of the tumors were plotted to illustrate the extent of overlap between them. Results: Comparison of plotted frequency distribution curves for thickness indicated that there are approximately 125 nevi for every melanoma in the TH range 1.5 to 2 mm, approximately 25 nevi for every melanoma in the TH range 2 to 2.5 mm and about 5 nevi for every melanoma in the TH range 2.5 to 3 mm. Similarly, comparison of the plotted frequency distribution curves for largest basal diameter of these tumor types indicated that there are approximately 70 nevi for every choroidal melanoma in the LBD range 5 to 6 mm, approximately 10 nevi for every melanoma in the LBD range 6 to 7 mm, and about 3 nevi for every melanoma in the LBD range 7 to 8 mm. Conclusion: Because of the markedly greater cumulative lifetime incidence of choroidal nevi, this analysis suggests considerable size overlap between larger nevi and smaller melanomas. Attempts to classify small melanocytic choroidal tumors clinically as benign nevi versus malignant melanomas on the basis of tumor size appear likely to result in multiple misclassifications.

Key Words: melanoma, epidemiology, statistics