Utility of Flow Cytometry (FC) in the Assessment of Therapeutic Efficacy in Myelodysplastic Syndromes (MDS) After Therapeutic Intervention.
Authors: Burbury Kate , Gambell Peter , Came Neil , Lynch Kevin , Seymour John F. , Prince Miles , Westerman David A 
Published: October 2019

Abstract
Abstract 2767
Poster Board II-743

Introduction:
The availability of effective disease-modifying therapies for patients with MDS, means standardised criteria for diagnosis, classification, prognostication and evaluation of treatment response are increasingly important. This has been achieved in part by the 2008 WHO classification. FC is now included as a co-criterion for diagnosis in the MDS consensus statement (Leuk Res 2007). Our aim was to explore the role of FC as a sensitive and objective tool for assessment of therapeutic efficacy.

Patients and Methods:
We prospectively and sequentially assessed the utility of FC during therapy, as part of two phase-II clinical trials incorporating 5-Azacytidine/Thalidomide and Lenalidomide/Stem-cell factor, respectively. Four-color FC analysis was performed on bone marrow samples using a defined antibody panel assessing blast and myelomonocytic populations. Antigen maturation patterns were evaluated by two independent assessors, comparing to healthy volunteers and normal patient controls (n=30), and assigned both a Wells FC score (wFCS) from 0–8 (Blood 2003) and Stachurski-FC score (sFCS) – denoted as positive, intermediate or negative for the presence of antigenic aberrancy and/or asynchrony (Leuk Res 2008).

Results:
31 patients, 20 males, median age 66 (range: 43–89) were included in the analysis. Within this cohort, there have been 112 FC assessments (incorporating both scores for each). There was good correlation of scoring between the 2 independent assessors with concordance of both FCS in 67/112 (61%) of evaluations. With regards to wFCS there was a discrepancy of 1 point between assessors in 38/112 (34%) of evaluations and 2 points in 2 evaluations (1.7%). For sFCS, there was a discrepancy in only 8/112 (7%) assays. WHO categories comprised: RA (n=1), RCMD (7), RAEB-I/II (13), CMML-I/II (4), 5q- (3), MDS-U (1), AML (2). IPSS cytogenetic risk categories: good – 21, intermediate - 4, poor - 4 and 2 non-assessable. According to WHO-Prognostic Scoring System (WPSS), no patient was at very low risk, 8 were low risk, and the majority classified with at least intermediate (n=6), high (n=12) and very high risk (n=6) disease. 30/31 (97%) were transfusion requiring at enrolment (29 red cell, 1 platelet), with median hemoglobin 92g/L (range 61–118), neutrophil count 2.13 (range 0.23–42), platelet count 195 (range 7–606) and marrow blasts 6% (range 1–28). Pre-treatment median wFCS was 6 (range: 3–9); and by sFCS, 24 were positive, 6 intermediate and 1 negative. At trial entry, the WFCS correlated with the percentage of marrow blasts (r=0.483, p=0.006) and the WPSS (r=0.35, p=0.055). 30 patients (97%) have been re-evaluated on therapy; median time to best clinical response (IWG-2008 criteria) was 77 days (range: 27–511), consistent with previous observations (Fenaux et al, Lancet Oncol 2009). Twenty (65%) achieved at least a PR by conventional criteria. Of these, 15 (75%) showed a concordant improvement in FCS (defined as a reduction in points allocated) in either or both of the wFCS and sFCS. Of these 11/15 showed a reduction in the wFCS (median reduction in score 2, range 1–3); 4 showed a concordant improvement in the assigned sFCS (from positive to intermediate, n=2; or intermediate to negative, n=2). Of those who achieved a response by conventional criteria, 2 patients showed no change in either FCS's and 3 patients (CR=1; PR=2) showed an increase in both FCS's, suggestive of early progression, 2 of whom have subsequently progressed clinically by conventional criteria. Of the 20 that achieved a response 18 (90%) have had further assessments. 5/18 (28%) have since progressed, with 80% showing concordant FCS deterioration. Of those who maintained stable disease by conventional criteria (10/31), 7 showed improvement in the either or both of the FCS. Two have since progressed and both showed a concordant deterioration in FCS.

Conclusions:
These data indicate that FC may offer a more subtle and dynamic objective assessment for sequential disease monitoring, and may aid MDS treatment response evaluation. Further large prospective clinical trials utilising immunophenotyping as a co-criterion to measure response are required to validate these findings.

Disclosures:
Lynch: Celgene Pty Ltd: Employment, Equity Ownership. Seymour:Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau.