TP53 Mutations Are Restricted Predominantly to 5q- Syndrome and Myelodysplastic Syndrome Patients with Complex Cytogenetics, and Correlate with Adverse Prognosis

Abstract 792

Myelodysplastic syndromes are clinically and molecularly heterogeneous group of disorders with variable prognosis and propensity to leukaemic transformation. We analysed the incidence and impact of TP53 gene mutations in a large cohort of MDS patients (n=318) using next generation sequencing (454 FLX).

The median age was 65 years (range 17–72 years) with a male to female ratio of 1.7:1.The median follow-up of this cohort was 18.7 months (range 1–74 months). Forty patients (12%) underwent disease modifying treatments (bone marrow transplant, intensive chemotherapy, 5-azacitidine and Lenalidomide) at the time of sample collection and hence survival analysis was censored at the date of such treatment. Twenty one (7%) has RA, MDS with isolated del 5q–26 (8%), RARS-13 (4%), RCMD/RCMD-RS-105 (32%), RAEB 1/2 −75 (24%), AML secondary to MDS-29 (9%), therapy related MDS (tMDS)-22(7%) and MDS/MPN 27 (9%). IPSS cytogenetic risk groups were; good risk-199(63%), intermediate −35 (11%) and poor risk-67 (21%) and cytogenetics failed in 17 patients (5%). The IPSS categories were, low risk: 71(24%), intermediate-1:101(32%), intermediate-2:58 (18%), high risk: 29 (9%) and 38 patients were not evaluable (proliferative CMML and MPD/MDS). Progression to AML occurred in 68 patients (20%).

TP53mutations were observed in 30 (9.4%) of MDS patients. Twenty of 30 (67%) mutations were detected in int-2/high risk IPSS groups and were associated with complex cytogenetics (73%). Rest of the mutations were detected in low/int-1 IPSS patients with isolated 5q- abnormality [5 of 26, (19%)].Of the 22 cases with t MDS, 6 had TP53 mutations and 17/91 (19%) patients with RAEB and AML with trilineage dysplasia harboured TP53 mutations. Only one patient each with RCMD and MDS/MPD-U had TP53 mutation.

Of the 39 mutations, 9 patients had two mutant P53 clones whereas 21 patients had single mutation. 30 of 36 (83%) mutations were located in the DNA-binding domain. Patients with therapy related MDS had increased likelihood (p<0.001) of having double mutations (5/22), while none of the patients with isolated 5q had double mutations (0/26).All except one patient (8 out of 9) with double mutations had a blast count of <10%.(p<0.001)

The median clone size of TP53 mutations were 42 %( range 2.5–93%) and the median clone size of patients with double mutations was 82%.Nine patients with TP53 mutation had sequential samples tested at variable time intervals post 5-azacitidine treatment to analyze clone size and correlate with clinical responses. Four patients showed a marked decrease in clone size (24 to 3%,25:44% to 4:6%,35; 40% to 8; 17%78% to 15%,) associated with cytogenetic remission, one patient showed a increase in clone size (60% to 93%) at the time of leukaemic evolution and the remaining four patients had stable TP53 clones after 5-azacitidine.

TP53 mutations strongly correlated with worse OS and PFS. The median OS for patients with wild type TP53 was not reached (NR,>66 months) compared with 9.7 months for patients with TP53 mutations (p<0.0001) and median PFS for patients with wild type TP53 was not reached (NR,>66 months) compared with 8.5 months for patients with TP53 mutations (p<0.0001).

A cytogenetic sub-group analysis was performed in patients with complex cytogenetics with or without mutations of TP53, and showed patients with mutation had a worse OS (9.6 vs. 14.1 months, p<0.0001) and PFS (8.3 vs. 13.9 months, p<0.001) compared with those with wild type TP53.

MDS with isolated deletion 5q harbouring a TP53 mutation(med OS 23 months) had significantly worse outcome compared with del5q patients without mutation(med OS 66 months)(p<0.002).

In a multivariate analysis using co-variables: age (>55yr vs <55 yr), sex, WHO subtypes, IPSS risk category, transfusion dependency, presence or absence of mutations, TP53 was found to be the strongest predictor for OS (HR-3.78, p<0.0001, CI 2.37–6.20) and PFS (HR-3.22, p<0.0001, CI 1.97–5.26).

This large single institution study confirms that TP53 mutations are an independent prognosticator of outcome in MDS. The adverse impact of TP53 persists after adjustment for cytogenetic risk and is of practical importance in evaluating the prognosis in patients with MDS. The relatively common occurrence of these mutations in different spectrums of MDS, ie isolated 5q- and complex cytogenetics, possibly implies two different mechanistic roles for p53 protein in disease evolution.