Chromosome instability in preleukemic states of adult T-cell leukemia (pre-ATL).

Chromosome analysis was performed on nine patients with subclinical adult T-cell leukemia (pre-ATL), who were asymptomatic ATL virus carriers. Fewer than 30% of their peripheral blood leukocytes were abnormal T-lymphocytes with nuclear abnormalities. ATL-associated antigen (ATLA) and anti-ATLA antibody were found in all patients. Eight had variable abnormal karyotypes in a fraction (5.0%-25.4%) of peripheral blood leukocytes stimulated with phytohemagglutinin or T-cell growth factor. There were no metaphases when a mitogen was not added. Four patients had a clonal chromosome abnormality. The chromosome abnormality seen in one patient was observed in the first study but not in a second study, when a different abnormality was seen. In five patients, an abnormal chromosome #14 with a break at band 14q11 was found. These findings indicate that unstable, chromosomally abnormal clones are characteristic of pre-ATL.