Background: We previously reported from a case-control analysis that T-cell non-Hodgkin's lymphoma (NHL) was strongly associated with human T-lymphotropic virus type I(HTLV-I) infection in Jamaica and Trinidad and that the relative risk for HTLV-I infection was very high in younger patients, Purpose: The objective of this study was to estimate the age-specific incidence rates of NHL among HTLV-I-infected and HTLV-I-uninfected adults in Jamaica and Trinidad, Methods: Population rates of HTLV-I infection were calculated from available census reports and serosurvey data, Incidence rates for NHL were calculated from all incident cases in Jamaica during 1984-1987 (n = 135) and from all incident cases in Trinidad during 1986-1990 (n 117), Using biopsy material, we determined whether the immunophenotype of the tumor cells was T cell, B cell, or other, NHL incidence rates were computed according to HTLV-I status, age, sex, and tumor phenotype for each country separately and for both countries combined by weighting to the relative population size of each country, Results: The age-standardized NHL incidence rate (mean +/- SE) in Jamaica was 1.9 +/- 0.2 per 100000 person-years (PY), In Trinidad, the rate was 2.9 +/- 0.4 per 100000 PY. Overall, the incidence of NHL increased with age and was higher in males than in females, In the HTLV-I-infected population, the incidence of NHL was inversely related to age, and age specific rates were higher in males than in females, The NHL incidence in those estimated to have acquired HTLV-I infection in childhood, however, showed no sex difference, and one in 1300 such carriers (95% confidence interval: one in 1100 to one in 1600) per annum were estimated to be at such risk, For T-cell NHL, as proxy for adult T-cell lymphoma/leukemia, incidence was highest in those patients infected with HTLV-I early in life (perinatally or via breast milk), with high, sustained risk from early adulthood in both sexes, Conclusions: While overall NHL incidence rates reveal that HTLV-I endemicity does not impose an exaggerated lymphoma burden on these populations, the risk for lymphoma among carriers who acquire infection early in life is dramatic and is consistent with the hypothesis that virus exposure early in life is most important for lymphomagenesis, Implications: Studies of HTLVI carriers known to be infected in childhood may provide insight into markers intermediate in the lymphoma-genetic process, Strategies to disrupt early-life transmission of HTLV-I, notably mother-infant transmission, may be critical in reducing the burden of lymphoreticular disease in these populations
