Background Factors affecting the risk of ocular non-Hodgkin lymphoma (NHL) are not well understood. A recent article reported a high prevalence of Chlamydia psittaci infection in patients with ocular NHL and complete remission or significant reduction of measurable lesions following C. psittaci-eradicating antibiotic therapy among these patients, thus suggesting a role for C. psittaci infection in the etiology of this rare cancer. Methods In order to search for etiologic clues, we analyzed population-based incidence data from the Surveillance, Epidemiology, and End Results (SEER) Program to assess ocular NHL rates and compare them to other extra-nodal and nodal NHL rates. Results During 1997-2001 in the nine SEER areas, the age-adjusted (2000 US Standard) ocular NHL rates were 0.29 (n=137) and 0.31 (n=179) per 100,000 person-years among white males and females, respectively. Ocular NHL rates showed little gender difference, in contrast to a male predominance among other extra-nodal (7.33 versus 4.94) and nodal (16.92 versus 11.60) NHL rates. Among whites, ocular NHL rates increased rapidly and steadily from the 1970s until 2001, at 6.2% and 6.5% per year among males and females, respectively, with no evidence of peaking. Nodal and non-ocular extra-nodal NHL rates also rose during the 1970s and 1980s, but nodal NHL rates plateaued in the 1990s. Non-ocular extra-nodal NHL rates among males also peaked in the mid-1990s, while rates among females continued to increase. Data from 11 SEER areas during 1992-2001 were used to calculate lymphoma rates among different racial/ethnic groups. Ocular NHL rates for both genders were highest among Asian or Pacific Islanders, followed by white non-Hispanics. Rates were lowest for white Hispanics among women and for blacks among men. Ocular NHL rates increased with age among all ethnic groups studied and rose more rapidly with age among Asian or Pacific Islanders, who had the highest rates at ages 30 to 60 years compared to all other ethnic groups. Among whites, in all age groups, ocular NHL rates were similar for both genders, in contrast to other extra-nodal and nodal NHL rates, which showed a male predominance at all ages. Ocular NHL rates for white males and females were notably lower in Utah, with little geographic variation elsewhere Conclusions Similar rates of ocular NHL among males and females of all racial/ethnic groups, which contrast with the male predominance observed for most other cancers, including other NHLs, cannot be readily explained. Ocular NHL rates continued to increase rapidly through the 1990s, in contrast with AIDS-related NHL rates that peaked in the 1990s. The racial/ethnic distributions of ocular NHL also differ from those of other NHLs. These unique characteristics of ocular NHL incidence suggest a different etiology for this malignancy compared to other lymphomas. Further investigation of the role of infectious agents, such as C. psittaci, is warranted and may help explain these observations.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]