Purpose: To describe the baseline characteristics and status of patients enrolled in the Collaborative Ocular Melanoma Study (COMS) randomized clinical trial of pre-enucleation radiation of large choroidal melanoma conducted in the United States and Canada, and to compare characteristics of patients enrolled with those of patients with tumors of eligible size who were not enrolled in order to assess the generalizability of findings from the clinical trial.

Methods: For all patients evaluated for the clinical trial at COMS centers from November 1986 through December 15, 1994, selected data were transmitted to the COMS Coordinating Center. For patients who enrolled in the clinical trial, ophthalmic and medical history, examination findings, and visual acuity measurements were recorded prior to enrollment. Standardized A-scan and contact B-scan echographic examinations were performed prior to enrollment, and photoechograms were submitted for central review for consistency with the diagnosis, independent measurement of the apical height of the tumor, and description of tumor configuration and internal reflectivity for each patient enrolled. Until January 1992, wide-angle fundus photographs and fluorescein angiograms taken prior to enrollment also were submitted for central review to confirm consistency with the diagnosis. All data were integrated and analyzed at the COMS Coordinating Center.

Results: Of 6,078 patients with choroidal melanoma evaluated in COMS centers, 1,860 had tumors of eligible size; of these, 1,302 (70%) were eligible for the clinical trial, and 1,003 (77% of eligible patients) enrolled. The two principal reasons for ineligibility were other primary cancer and predominantly ciliary body melanoma. Ineligible patients were older than eligible patients, had larger choroidal melanoma, and had poorer visual acuity at the time of evaluation for the COMS (P < .01, Wilcoxon rank sum tests). Patients eligible for the clinical trial had a mean age of 60 years; 56% were male; almost all (97%) were non-Hispanic whites. Among eligible patients, mean tumor apical height was 9.5 mm and mean longest basal diameter was 17.2 mm. Eligible patients who enrolled in the trial were similar to eligible patients who did not enroll with respect to most factors considered. Those who enrolled had longer tumor basal diameter and better visual acuity in the fellow eye, more often had their primary residence in Canada, and less often had education beyond high school than did eligible patients who did not enroll (P < .05, Wilcoxon rank sum tests and χ² tests, respectively).

Conclusions: The COMS clinical trial of pre-enucleation radiation was designed to yield internally valid treatment comparisons through random treatment assignment at time of enrollment. Findings also have high external validity because a majority (54%) of all patients with tumors of eligible size, and a large majority (77%) of all eligible patients, were enrolled. Furthermore, patient characteristics are similar to those of patients included in other evaluations of this method of treating large choroidal melanoma. Thus, findings from this clinical trial apply to all patients who have large choroidal melanoma and satisfy COMS eligibility criteria.