Many papers on retinoblastoma open with a statement that it is the most common primary intraocular cancer in children and a rare disease. True enough. After reflecting a little longer on the epidemiology of eye cancer, however, this statement probably should be revised to read: “retinoblastoma is the most frequent primary intraocular cancer and is gaining importance rapidly.” Let us substantiate this claim and evaluate its consequences in some detail.

First, just how frequent is retinoblastoma? Not an easy question to answer because investigators are estimating its incidence in many ways. A recent issue featured two papers on the subject from the Western hemisphere. MacCarthy and coworkers,1 who analysed data from 1601 children with retinoblastoma diagnosed in England, Scotland and Wales between 1963 and 2002, arrive at an annual incidence rate of 3.5 per million children less than 15 years of age. Broaddus and colleagues2 from the USA estimate the rate to be 11.8 per million children below 5 years of age, based on 658 entries in the Surveillance, Epidemiology, and End Results (SEER) programme database from 1975 to 2004.

MacCarthy and coworkers also provide a cumulative incidence estimate of 53 per million for the first 14 years of life, which is useful because by that age, essentially all retinoblastomas have been detected, and they report that 95% of tumours were diagnosed before the age of 5 years.1 Presuming that this percentage is constant, one can calculate the corresponding estimate to be 62 per million for the SEER study. Although they are of the same order of magnitude, the estimates, or any estimate based on the number of children of particular age, will be influenced by differences in child and adolescent mortality between countries, the more so the wider is the age cohort considered.

Because retinoblastoma is …