FISH studies using LSI bcl-2/IgH probe allowed quantifying the clonal cell population with this rearrangement (4% and 6.6% of cells at diagnosis and RT, respectively).
Southern blot hybridization analysis failed to show evidence of bcl-1, bcl-2, c-myc proto-oncogene or retinoblastoma (Rb) tumor-suppressor gene rearrangements in these six cases of Richter's syndrome.