Latitude gradients for lymphoid neoplasm subtypes in Australia support an association with ultraviolet radiation exposure

Given the uncertainty surrounding solar ultraviolet radiation (UVR) exposure and risk of lymphoid neoplasms, we performed an ecological analysis of national Australian data for incident cases diagnosed between 2002 and 2006. Subtype-specific incidence was examined by latitude band (<29 degrees S, 29-36 degrees S, 37 degrees S), a proxy for ambient UVR exposure, using multiple Poisson regression, adjusted for sex, age-group and calendar year. Incidence increased with distance from the equator for several mature B-cell non-Hodgkin lymphomas, including diffuse large B-cell [incidence rate ratio (IRR)=1.37; 95% confidence interval (CI): 1.16-1.61 for latitude 37 degrees S relative to <29 degrees S], lymphoplasmacytic (IRR=1.34; 95% CI: 1.12-1.61), mucosa-associated lymphoid tissue (IRR=1.32; 95% CI: 0.97-1.80) and mantle cell lymphoma (IRR=1.29; 95% CI: 1.05-1.58), as well as plasmacytoma (IRR=1.52; 95% CI: 1.09-2.11) and plasma cell myeloma (IRR=1.15; 95% CI: 1.03-1.27). A similar pattern was observed for several mature cutaneous T-cell neoplasms, including primary cutaneous anaplastic large cell lymphoma (IRR=4.26; 95% CI: 1.85-9.84), mycosis fungoides/Sezary syndrome (IRR=1.72; 95% CI: 1.20-2.46), and peripheral T-cell lymphoma not otherwise specified (NOS) (IRR=1.53; 95% CI: 1.17-2.00). Incidence of mixed cellularity/lymphocyte-depleted (IRR=1.60; 95% CI: 1.16-2.20) and nodular sclerosis Hodgkin lymphoma (IRR=1.57; 95% CI: 1.33-1.85) also increased with distance from the equator. Many of these subtypes have a known association with infection or immune dysregulation. Our findings support a possible protective effect of UVR exposure on the risk of several lymphoid neoplasms, possibly through vitamin D-related immune modulation critical in lymphomagenesis.