Abstract
Adult T-cell leukemia-lymphoma (ATL) is an aggressive T-cell malignancy caused by human T-cell leukemia virus type 1 (HTLV-1) infection that often occurs in HTLV-1-endemic areas, such as Japan, the Caribbean islands, Central and South America, Intertropical Africa, and the Middle East. In Japan, the nationwide estimation of the number of HTLV-1 carriers was at least 1.08 million in 2006–2007. Furthermore, in 2016, the nationwide annual incidence of newly infected with HTLV-1 was first estimated to be 3.8 per 100,000 person-years based on the age-specific seroconversion rates of blood donors in almost all areas of Japan. The incidence rate was three times higher in women than in men, and it was estimated that at least 4,000 new HTLV-1 infections occur yearly among adolescents and adults in Japan. As well known that HTLV-1 infection alone is not a sufficient condition for ATL to develop. To date, a variety of molecular abnormalities and host susceptibilities have been reported as candidate progression factors for the development of ATL in HTLV-1-carriers. In particular, quite recently in Japan, a variety of immunosuppressive conditions have been recognized as the most important host susceptibilities associated with the development of ATL from HTLV-1-carrier status. Furthermore, in 2013–2016 in Japan, a new nationwide epidemiological study of ATL was conducted targeting patients newly diagnosed with ATL in 2010–2011, from which the most current knowledge about the epidemiological characteristics of Japanese patients with ATL was updated as follows: (1) continuing regional unevenness of the distribution of people with HTLV-1, (2) further aging, with the mean age at diagnosis being 67.5 years, (3) declining M/F ratio, (4) increase of the lymphoma subtype, (5) sex differences in subtype distribution, (6) age differences in subtype distribution, and (7) comorbidity condition. In particular, 32.2% of ATL patients had comorbid malignancies other than ATL. However, the number of deaths due to ATL in Japan has been relatively stable, at around 1,000 patients annually, without significant decline from 1999 to 2017. Because the current epidemiological evidence about HTLV-1 and ATL is insufficient, further epidemiological studies are required.
Highlights
Adult T-cell leukemia-lymphoma (ATL) is a T-cell malignancy caused by human T-cell leukemia virus type 1 (HTLV-1)
The establishment of the etiological association between HTLV1 infection and ATL was based on the following epidemiological and clinical facts: (1) all patients with ATL have antibodies against HTLV-1 (Hinuma et al, 1981, 1982), (2) geographical areas of high incidence of patients with ATL closely correspond with areas of high incidence of HTLV-1 carriers (The T, and BCell Malignancy Study Group, 1985), (3) HTLV-1 immortalizes human CD4 T cells in vitro (Hattori et al, 1981), and (4) all ATL cells have monoclonal integration of HTLV-1 proviral DNA (Yoshida et al, 1984)
Existing published data regarding predisposing factors and genetic abnormalities are still insufficient to explain the characteristics of ATL oncogenesis
Summary
Adult T-cell leukemia-lymphoma (ATL) is a T-cell malignancy caused by human T-cell leukemia virus type 1 (HTLV-1). Hashimoto et al (1991) investigated the nationwide age-specific prevalence of HTLV-1 by including approximately 610,000 blood donations from the entire area of Japan, confirming that the HTLV-1 seroprevalence was higher in female than male individuals and that the prevalence was higher in older people (Table 1). The most recent age-specific HTLV-1 prevalence and estimated number of HTLV-1-infected people in whole Japan were reported by Satake et al (2012) based on the HTLV1 screening test results from approximately 1,200,000 blood donations during 2006–2007 throughout all of Japan. The positive rate was from 0.12 to 1.59% for male donors and from 0.11 to 2.36% for female donors in age brackets ranging from 16–19 to 90–99 years (Table 1) Based on those age-specific HTLV-1 seroprevalence rates during 2006–2007, Satake et al estimated that the number of HTLV1 carriers was at least 1.08 million in Japan in 2006–2007. Stuver et al (1993) reported that the HTLV-1 seroconversion rate was 4.9 per 100 person-years among seronegative wives with seropositive husbands but 1.2 per 100 person-years among seronegative husbands with seropositive wives in a prospective cohort study of 534 older married couples in Miyazaki Prefecture, Kyushu
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