The sensitivity of chronic lymphocytic leukaemia lymphocytes to irradiation in vitro.

The inhibition of [3H]-thymidine incorporation into the DNA of mitogen-stimulated chronic lymphocytic leukaemia lymphocytes by chlorambucil or gamma-irradiation in vitro was measured in a series of patients, some of whom were untreated, some treated and some who were showing resistance to first-line or second-line treatment. There was evidence of resistance to irradiation developing in parallel with that to chlorambucil. The resistance to chlorambucil in chronic lymphocytic leukaemia (CLL) is not necessarily due to altered drug transport or metabolism but to a more fundamental process affecting DNA damage.