Although the expression of CD19, ERK1/2 or STAT3, known to be the HSP90 non-client proteins, remained unaltered upon HSP90-inhibition (Figure 2C), phosphorylation of ERK1/2 was significantly reduced in CLL cells likely, as a result of interruption of the BCR signal. Here, CD19 is linked to B-cell chronic lymphocytic leukemia.