Adult T‐cell leukaemia/lymphoma in Brazil: A rare disease or rarely diagnosed?

Adult T-cell leukaemia/lymphoma (ATL), caused by human T-cell lymphotropic virus type 1 (HTLV-1) infection has a median survival of 6–8 months. In Japan the incidence of ATL is about 10 times higher than HTLV-1-associated myelopathy (HAM) whilst in other regions the incidence of these consequences is similar. Brazil has a high prevalence of HTLV-1 with HAM cohorts described, but reports of ATL are sparse, leading to the concept that the incidence of ATL is low. Here, the number of ATL cases in Brazil was estimated and compared with cases in the national registry of cancer (RHC) (Minist erio da Sa ude do Brasil, 2012). Whether the incidence of ATL is genuinely low or ATL is under-diagnosed is discussed. First, using published estimates of HTLV-1 infected individuals in Brazil: 800,000 (Gessain & Cassar, 2012) – 2,500,000 (Carneiro-Proietti et al., 2002) and a life-time ATL risk of 4% (Iwanaga et al., 2012), 32,000–100,000 can be expected to develop ATL. Based on 75 years life expectancy in Brazil, 427–1,333 cases of ATL/year are expected. Second, ATL development is linked with mother-to-child transmission. Only 12 % of infections were considered to be acquired through this route but these 96,000–300,000 infant infections carry as much as 20% life-time ATL risk (Nunes et al., 2017). Thus, 19,200–60,000 carriers would develop ATL resulting in 256–800 cases/year. Third, ATL cases were estimated accounting for differences in HTLV-1 prevalence between Brazil‘s regions, age and gender, resulting in 856 ATL cases/year (Table I and Table S1). However, from 1986–2016 only 369 ATL cases were reported in RHC an average of 12 per year (https://irhc.inca. gov.br/RHCNet/visualizaTabNetExterno.action) (Fig 1). Their age ranged from months to >85 years, with 8 4% of cases in