Clinical, Laboratory, and Treatment Outcome Characteristics of Chronic Lymphocytic Leukemia (CLL) Patients with p53 Mutations or del(17p) Enrolled on a Prospective Phase III Clinical Trial: Short Progression Free Survival, Irrespective of Fludarabine-Based Treatment Used.
Authors: Lucas David M. , Dewald Gordon W. , Neuberg Donna S. , Byrd John C. , Lozanski Gerard , Harbison Jennifer , Cunningham Kammy D. , Flinn Ian W. , Tallman Martin S. , Grever Michael R. 
Published: October 2019

Deletions or mutations of the tumor suppressor p53 have been associated with more aggressive disease in many types of cancer including CLL, and are more commonly found in relapsed or refractory patients. We studied symptomatic patients (pts) enrolled on ECOG 2997, a randomized phase III trial of fludarabine monotherapy (F) versus fludarabine plus cyclophosphamide (CF) for previously untreated CLL. A total of 235 pretreatment samples were analyzed for p53 mutations in exons 5–9 using denaturing gradient gel electrophoresis (DGGE), followed by confirmation of mutations using automated sequencing. Cytogenetic analysis was also performed on 243 patient samples by Fluorescence In Situ Hybridization (FISH) using a probe to detect deletions in 17p13.1, the chromosomal location of the p53 gene. In the analysis by DGGE, a total of 25 pts (10.6%) were found to have p53 mutations. In 22 cases there was a single mutation, and in three cases there were two mutations. Mutations in exon 6 were the most common, and in each of the cases with two mutations, one of these was in exon 6. Results by exon are as follows: Exon 5 (1 pt, 0.4%), Exon 6 (15 pts, 6.4%), Exon 7 (5 pts, 2.1%), Exon 8 (3 pts, 1.3%), Exon 9 (4 pts, 1.7%). The interphase cytogenetic analysis included 24 of the 25 pts with a p53 mutation by DGGE. Of the 19 (7.8%) pts with del(17p13.1) as the leading cytogenetic anomaly, seven were cases that also had mutations in p53 by DGGE. The remaining 17 pts with mutations in p53 by DGGE had as leading cytogenetic anomaly: del(11q) (2 pts); trisomy 12 (3 pts), normal cytogenetics (2 pts), and del(13q) (10 pts). Results from both the DGGE and FISH analyses were combined to identify a group of 37 pts with either del(17p) or p53 mutation. This constituted 16% of the 230 pts in which either FISH or p53 mutational analysis was performed.

Immunocytochemistry staining for p53 was performed on all pts, and no correlation was found between over-expression of p53 protein with mutation and/or deletion of this gene. The pts were then assessed by treatment arm for response and progression-free survival (PFS), relative to patients without p53 abnormality either by DGGE or FISH analysis. In the FC group: 13 pts had either a p53 mutation or del(17p), nine (69%) of whom achieved a CR or a PR, versus 56/74 (76%) of those with normal p53 (p=0.73). In the F group: 15 pts had either a p53 mutation or del(17p), of whom four (27%) achieved a CR or a PR, versus 38/70 (54%) of those with normal p53 (p=0.09). Pts with a detectable abnormality in p53 had a significantly reduced PFS, regardless of whether they received fludarabine alone (p=0.02) or fludarabine plus cyclophosphamide (p=0.005). This study suggests that routine immunocytochemistry staining should not be substituted for p53 mutational studies. While some short responses were observed in patients with p53 mutation and/or deletion receiving fludarabine and/or fludarabine cyclophosphamide, the time to progression was significantly shorter, emphasizing the prognostic significance of p53 abnormalities for this disease.