Development of adult T-cell leukemia in a patient with rheumatoid arthritis treated with tocilizumab.

Tocilizumab (TCZ) was administered from 2004 to 2008 in a 52-year-old woman with rheumatoid arthritis (RA) refractory to methotrexate (MTX) as a clinical trial. TCZ therapy with MTX was resumed in March 2009 due to exacerbation of RA. The patient was an human T-lymphotropic virus type I (HTLV-I) carrier, and, in April 2011, a peripheral blood smear showed many atypical lymphocytes, thus leading to a diagnosis of adult T-cell leukemia (ATL). Complete remission of ATL was achieved with a standard therapeutic regimen.