Frequency of Clonal Evolution by FISH in Untreated, Early Stage Patients with CLL: A Prospective, Longitudinal Study with Long Clinical Follow-Up.

Background: Using fluorescent in-situ hybridization (FISH), a number of investigators have identified specific cytogenetic abnormalities that identify CLL patients with a more aggressive (17p-, 11q-) or indolent (13q-) disease course. Some have suggested patients who initially have a normal karyotype may acquire new chromosome abnormalities during the course of their disease. Since patients with specific cytogenetic abnormalities (17p-, 11q-) are less likely to respond to purine nucleoside analogues, such clonal evolution has potential implications for treatment as well as prognosis. No study has prospectively investigated the frequency of clonal evolution in a cohort of patients with newly diagnosed untreated CLL.

Methods: Between 1994 and 2000, we enrolled 167 patients with previously untreated CLL seen at Mayo Clinic in a prospective trial evaluating the prognostic importance of cytogenetic abnormalities and clonal evolution detected by FISH. All patients provided a baseline blood specimen for FISH testing and follow-up specimens over the following 24 months. Other research samples from later timepoints were tested where available. Study participants were contacted by mail in 2004 to update vital and treatment status. Of 83 living responders, 70 (84%) indicated they would be willing to provide an additional follow-up sample for cytogenetic analysis of whom 48 have returned a sample to date. Results of clinical FISH testing during the follow-up interval were also abstracted. FISH was performed on interphase nuclei from blood as we have previously described (BJH 121:287).

Results: Median age at diagnosis was 64. Median time from diagnosis to study enrollment was 3.3 months. 94% of patients had early stage disease at enrollment (88 Rai 0; 48 Rai I, 18 Rai II, 2 Rai III; 8 Rai IV). Median follow-up time from diagnosis for all 164 eligible study participants was 8.5 years (range: 0.33–22.9 yrs). As of last follow-up, 48% of patients have received treatment and 57 (35%) have died. 75% of patients had chromosome abnormalities on FISH testing at baseline. The frequency of individual cytogenetic abnormalities on baseline FISH analysis along with overall survival by hierarchical FISH risk category are shown in Table I. 106 patients had sequential samples for FISH analysis at least 2 years apart, 61 had samples at least 5 years apart, and 22 had samples at least 10 years apart. 15 patients had evidence of clonal evolution during follow up as evidenced by a new FISH anomaly not present on the baseline specimen. No clonal evolution was observed in the first 2 years of follow-up (n=106), however of 61 patients with samples at least 5 years apart, 14 (23%) had evidence of clonal evolution. Median time for development of a new cytogenetic abnormality among these patients was 9.3 years.

Conclusions: Clonal evolution occurs during the course of disease for approximately 25% of patients with early stage CLL. Clonal evolution appears to occur at low frequency during the first 2 years of follow-up but increases in frequency after 5 years. This finding has potentially significant implications for prognosis and treatment of patients with CLL.