Adult T-cell leukemia

Overview
Human T cell leukemia/lymphotropic virus type 1 (HTLV-1) is believed to be the cause of several diseases, including adult T cell leukemia/lymphoma (ATLL), a rare cancer of the immune system's own T-cells.

ATLL is usually a highly aggressive non-Hodgkin's lymphoma with no characteristic histologic appearance except for a diffuse pattern and a mature T-cell phenotype. Circulating lymphocytes with an irregular nuclear contour (leukemic cells) are frequently seen. Several lines of evidence suggest that HTLV-1 causes ATLL. This evidence includes the frequent isolation of HTLV-1 from patients with this disease and the detection of HTLV-1 proviral genome in ATLL leukemic cells. ATLL is frequently accompanied by visceral involvement, hypercalcemia, lytic bone lesions, and skin lesions. Most patients die within one year of diagnosis.

Infection with HTLV-1, like infection with other retroviruses, probably occurs for life and can be inferred when antibody against HTLV-1 is detected in the serum.

Incidence/prevalence
HTLV-1 infection in the United States appears to be rare. Although little serologic data exist, prevalence of infection is thought to be highest among blacks living in the Southeast. A prevalence rate of 30% has been found among black intravenous drug abusers in New Jersey, and a rate of 49% has been found in a similar group in New Orleans. It is possible that prevalence of infection is increasing in this risk group. Studies of HTLV-1 antibody indicate that the virus is endemic in southern Japan, in the Caribbean, and in Africa.

ATLL is relatively uncommon among those infected with HTLV-1. The overall incidence of ATLL is estimated at about 1 per 1,500 adult HTLV-1 carriers per year. Those cases that have been reported have occurred mostly among persons from the Caribbean or blacks from the Southeast (National Institutes of Health, unpublished data). There appears to be a long latent period between HTLV-1 infection and the start of ATLL.

Transmission
Transmission of HTLV-1 is believed to occur from mother to child; by sexual contact; and through exposure to contaminated blood, either through blood transfusion or sharing of contaminated needles.