An apparent small cluster of choroidal melanoma cases.

Three choroidal melanomas were detected in a 2.5-year period in a small community of 3,592 persons. This small cluster represented an incidence about 20 times that expected (P = .0006). The community has an isolated water supply and very little industry. We determined the incidence of cancer in this and two adjacent communities and found no other unexpectedly high incidence. The three patients had no common exposures. Analyses of air and water from the involved community by mass spectroscopy, chromatography, and Ames (mutagenicity) tests were noncontributory. Nine of 60 mice given community water after weaning developed lens opacities eight to 16 months later; electron microscopy showed an abnormal monolayer of cells on the outer surface of the anterior lens capsule. The genesis of this monolayer was not clear. None of the 30 controls showed such lesions.