Interobserver variance in myelodysplastic syndromes with less than 5 % bone marrow blasts: unilineage vs. multilineage dysplasia and reproducibility of the threshold of 2 % blasts.

Previous studies have shown the reproducibility of the 2008 World Health Organization (WHO) classification in myelodysplastic syndromes (MDS), especially when multilineage dysplasia or excess of blasts are present. However, there are few data regarding the reproducibility of MDS with unilineage dysplasia. The revised International Prognostic Scoring System R-IPSS described two new morphological categories, distinguishing bone marrow (BM) blast cell count between 0-2 % and >2- < 5 %. This distinction is critical for establishing prognosis, but the reproducibility of this threshold is still not demonstrated. The objectives of our study were to explore the reliability of the 2008 WHO classification, regarding unilineage vs. multilineage dysplasia, by reviewing 110 cases previously diagnosed with MDS, and to study whether the threshold of ≤2 % BM blasts is reproducible among different observers. We used the same methodology as in our previous paper [Font et al. (2013) Ann Hematol 92:19-24], by encouraging investigators to include patients with <5 % BM blasts. Samples were collected from 11 hospitals and were evaluated by 11 morphologists. Each observer evaluated 20 samples, and each sample was analyzed independently by two morphologists. Discordance was observed in 36/108 suitable cases (33 %, kappa test 0.503). Diagnosis of MDS with unilineage dysplasia (refractory cytopenia with unilineage dysplasia (RCUD), refractory anemia with ring sideroblasts (RARS) or unclassifiable MDS) was assessed in 33 patients, by either of the two observers. We combined this series with the cases with RCUD or RARS included in our 2013 paper, thus obtaining 50 cases with unilineage dysplasia by at least one of the observers. The whole series showed very low agreement regarding RCUD (5/23, 21 %) and RARS (5/28, 18 %). Regarding BM blast count, the threshold of ≤2 % was not reproducible (discordance rate 32/108 cases, kappa test 0.277). Our study shows that among MDS WHO 2008 categories, interobserver discordance seems to be high in cases with unilineage dysplasia. We also illustrate that the threshold of ≤2 % BM blasts as settled by the R-IPSS may be not easy to reproduce by morphologists in real practice.