ASXL1 Mutations in Myelodysplastic Syndromes with 1% or More Ring Sideroblasts: Prevalence, Clinical Correlates and Prognostic Relevance

Background: Addition of sex combs-like 1 (ASXL1) is frequently mutated (mutational frequency 14-29%) and is prognostically relevant in myelodysplastic syndromes (MDS) (Bejar, NEJM 2011, Thol, JCO 2011). The prevalence and prognostic impact of ASXL1 mutation in MDS with ring sideroblasts (MDS-RS) is not known. MDS-RS is defined by the presence of ≥15% RS in bone marrow (BM), with refractory anemia with ring sideroblasts (RARS) being the prototype but may also be seen in other categories.

Methods: Our institutional database was reviewed to identify patients with WHO-defined primary MDS with ≥1% BM RS. Pathology slides, including iron stains, were reviewed to accurately quantify BM RS percentage and confirm WHO morphologic categories. All patients were annotated for their mutational status including ASXL1, JAK2, MPL and IDH with a subset for SF3B1 by PCR sequencing performed on BM specimens obtained at diagnosis.

Results:

i) Patient characteristics: A total of 76 MDS patients displayed ≥1% BM RS (median age 72 years; 76% males); 51 (67%) patients had ≥15% BM RS. IPSS-R risk categories for the entire 76 study patients were 30% very low, 37% low, 14% intermediate, 11% high and 8% very high; IPSS-R karyotype was normal in 63%, very good/good risk 17%, intermediate risk 12%, and poor/very poor in 8%; 3% had monosomal karyotype.

ii) Prevalence of ASXL1 mutations: Twenty-one (28%) of the 76 study patients were ASXL1 mutated; ASXL1 mutational frequencies were 25% (16/63 patients) in the absence and 38% (5/13 patients) in the presence of excess blasts (P=0.34). When considering only those patients with ≥15% BM RS (n=51), ASXL1 mutations were detected in 12 (24%) patients with mutational frequencies of 24% (11/46 patients) in the absence and 20% (1/5 patients) in the presence of excess blasts (P=0.84); ASXL1 mutational frequencies were 13% (3/23 patients) in RARS and 37% (7/19 patients) in RCMD-RS (P=0.07).

In terms of other mutations, all 76 study patients were wild-type for JAK2 and MPL, whereas IDH2 R140Q mutations were present in 4 (5%) patients, including 3 with concomitant ASXL1 and IDH2 mutations. IDH1 mutation was seen in only 1 patient. 25 of 43 (58%) patients screened were mutated for SF3B1, including 4 (9%) who were mutated for both ASXL1 and SF3B1. Significant associations were evident between ASXL1 and IDH2 mutations (P=0.02) but not between ASXL1 and SF3B1 mutations (P=0.61).

iii) Clinical correlates of ASXL1 mutations: Among all 76 study patients, presence of ASXL1 mutation did not correlate with age (P=0.30), hemoglobin level (P=0.17), platelet count (P=0.53), BM blast percentage (P=0.17), WHO morphologic category (P=0.34), transfusion dependence (P=0.84), IPSS-R cytogenetic categories (P=0.93), or IPSS-R risk group (P=0.33). The results were unchanged when analyzing the 51 patients with MDS-RS (i.e. ≥15% BM RS). Amongst the ASXL1 mutated patients (n=21) IPSS-R cytogenetic categories were as follows: 13 patients with normal karyotype (62%), 2 patients with trisomy 8 (10%), 1 patient each with –Y, del(11q), del(5q), del(20q), isochromosome 17 and monosomy 7 (5% each).

iv) Prognostic impact of ASXL1 mutations: Median follow-up was 42.5 months, during which time 69 (91%) deaths and 8 (11%) leukemic transformations were documented. ASXL1 mutated patients had a median survival of 29 months, compared to 45 months in ASXL1 wild-type patients (P=0.04). However, the difference in median survival was no longer significant during multivariable analysis, which instead identified only IPSS-R and transfusion need as being independent predictors of inferior survival. Amongst those patients without excess blasts (n=63), presence of ASXL1 mutation predicted inferior survival in univariate analysis (P=.04) and significance was sustained during multivariable analysis that included IPSS-R cytogenetic categories (P=.04) but became borderline when WHO morphologic category was included (P=0.06); ASXL1 mutated patients had a shortened median survival of 43 months compared to 66 months in ASXL1 wild-type patients (P=.04). In the presence of ≥15% BM RS, ASXL1 mutations did not affect survival (P=0.48); the results were the same for RARS (P=0.9) and RCMD-RS (P=0.64).

Conclusions: ASXL1 mutations might not affect survival in MDS patients with ≥15% BM RS, including those with RARS or RCMD-RS. Furthermore, an apparent survival disadvantage seen in ASXL1-mutated MDS patients with ≥1% BM RS was accounted for by IPSS-R.