Geospatial analyses demonstrate variation of cutaneous T-cell lymphomas across Australia, providing insights into possible causes.

Background: Cutaneous T-cell lymphomas (CTCLs) are rare with distinct diagnostic challenges. Equitable access to cancer care is a recognized priority, internationally. To date, the geospatial distribution of CTCL has not been definitively studied. Understanding the incidence and geographical distribution of patients with CTCL are critical first steps towards the ultimate goal of equity of care. Geospatial analyses also allow the opportunity to explore environmental causative factors: for CTCL, the contribution of solar ultraviolet (UV) radiation on causation remains unclear.

Objectives: We investigate geospatial patterns of CTCL incidence across Australia, compare with all rare cancers, and consider solar UV exposure on causality and diagnosis rates.

Methods: All CTCL diagnoses (1 January 2000 to 31 December 2019) were obtained from the nationwide dataset. Areas of residence were collected according to nationally approved definitions. Bayesian spatial incidence models were applied. Geospatial distributions were visually analysed.

Results: The CTCL age-standardised incidence rate was 7.7 (95% confidence interval 7.4-7.9) per million people per year in Australia. Diagnostic disparity was seen between Australian states/territories, with lower diagnosis rates in rural/remote and socioeconomically disadvantaged areas. Incidence exceeded the national average within more densely populated capital cities. Visual comparisons of the geospatial distribution of CTCL revealed marked discordances with the geospatial patterns of all rare cancers and solar UV in Australia.

Conclusions: Geographical heterogeneity in CTCL exists across Australia. Incidence reflects population density. Geospatial patterns of CTCL differ substantially from all rare cancers, with implications for the unique diagnostic challenges and unmet needs of this patient population. The distribution of CTCL across Australia does not support a causative link with UV exposure. Further global evaluation of geospatial patterns is warranted.