A Distinct Immunophenotypic Profile Of Del(5q) MDS Allows For Fast Monitoring Of Response To Treatment With Lenalidomide Or Azacitidine

Patients with MDS harboring a del(5q) often display characteristic morphological features in the bone marrow. For the first time we have recently demonstrated a strong association of the presence of a cytogenetic abnormality - del(5q) - with a specific 5-parameter immunophenotypic profile measured by flow cytometry (FCM). The aim of this prospective study was to test, if this FCM profile could also be applied for monitoring response to treatment with disease-modifying drugs like lenalidomide and azacitidine.

Overall, 137 FCM investigations were performed in 52 well-characterized patients with MDS and a del(5q) (IPSS low/int-1: n=30, int-2/high: n=22) including 34 patients with isolated del(5q): 53 measurements before treatment and 84 during treatment (lenalidomide=47 and/or azacitidine=35; chemotherapy and/or allogeneic transplantation=6). Nineteen of 41 thereupon evaluated patients showed a concomitant TP53 mutation. An 8-color/5-tube FCM diagnostic procedure (lyse-stain-wash) was performed on a FACS-Canto II cytometer. Thus, the typical del(5q) FCM profile includes the following 5 parameters: percentage of myeloid progenitors (myPC > 2%) = 3 points, CD45 MFI ratio (lymphocytes : myPC ≤ 7.0) = 10 points, SSC ratio (granulocytes : lymphocytes < 6.0) = 2 points, CD71 (≤ 20%) on granulocytes = 1.5 points, and female gender = 1.5 points. The weighting of these parameters has been done using a logistic regression model.

In 48/53 (92%, mean score=16.5±2.0) of the FCM measurements before therapy del(5q) was predictable with the 5-parameter FCM score. In the few FCM inconclusive cases the mutational analysis showed a TP53 mutation. Remarkably, in all 18 cases being in cytogenetic complete remission (CCR) in response to therapy the disappearance of del(5q) by conventional cytogenetic analyses was accompanied by the disappearance of the del(5q) FCM profile (specificity=100%; mean score=13.0±1.0). On the other hand, in patients without CCR during treatment the presence of del(5q) could be predicted by the FCM-score (≥ 15) with a sensitivity of 65% (43/66; mean score=15.5±3.0). Of note, in most of those inconclusive measurements (85%) a mutation of the TP53 gene and/or a deletion of chromosome (17p) could be detected suggesting a modification of the immunophenotype mediated by these molecular changes. Interestingly, the complexity of karyotypic abnormalities appeared to play a minor role in modifying the immunophenotype because in two-thirds of the FCM inconclusive cases del(5q) was present as a single abnormality.

The proposed 5-parameter del(5q) FCM profile can serve as a surrogate for the presence of a del(5q) and could therefore be used as a rapid tool for response monitoring during treatment with disease-modifying drugs. The role of TP53 mutations in modifying the FCM-profile in this context should be the purpose of further investigations.

No relevant conflicts of interest to declare.