Abstract
According to the World Health Organization (WHO) 2008/2016 criteria for classification of myeloid neoplasms, a platelet (PLT) count ≥ 450X109/l, thus reduced from the previous WHO 2001 level ≥ 600 x 109/l, was considered the new PLT threshold for the diagnosis of Essential Thrombocythemia (ET).
Aim of the study was to validate in a setting of current clinical practice this important diagnostic change and compare clinical and hematological features at diagnosis and during follow-up of patients with PLT ≥600 x 109/l versus patients with PLT < 600 x 109/l.
We retrospectively analyzed data from 264 patients with ET according to WHO 2008/2016 criteria, enrolled in our center from 1/2008 to 12/2017. Patients were divided into Group A (G-A) (PLT ≥600 x 109/l at diagnosis) (199 patients - 75.4%) and Group B (G-B) (PLT ≥ 450 x 109/l < 600 x 109/l at diagnosis) (65 patients - 24.6%) and compared for clinical features at the onset, clinical course and follow-up.
Main features and commonly recognized pro-thrombotic risk factors at diagnosis of the entire cohort as well as of G-A and G-B are reported in the Table 1. Among clinical features, only the median value of leukocytes was significantly higher in G- A [9.1 x 109/l, interquartile range (IQR) 7.8-10.3 vs 7.4 x 109/l, IQR 6.0-9.6; p = 0.001]. Among pro-thrombotic risk factors, only the median cholesterol value was significantly lower in the G-A [187 mg/dl (IQR 164-220) vs 204 mg/dl (RIQ 177-238); p = 0.048]. Cytostatic treatment was administered in 175 patients (71.1%) of entire cohort at different intervals from diagnosis, with a significantly higher rate in patients of G-A (76.9% versus 49.2%, p <0.001). After a median follow-up of 37.5 months (IQR 19.8 - 60.7), 13 thrombotic events (4.9%) were recorded in the entire cohort (7 episodes in the G-A and 6 episodes in the G-B), with a 5-year Cumulative Incidence of Thrombosis (CIT) significantly higher in the G-B [79.6% (95%CI 59.6 - 99.6) versus 95.4% (95%CI 91.8 - 99.0); p=0.047] (Figure 1). No patient evolved in myelofibrotic phase, 2 patients evolved in blastic phase (BP) after 42 and 58 months, respectively [1 patient (0.5%) in the G-A and 1 patient (1.3%) in the G-B; p=0.40). At the last follow-up, 4 patients (1.5%) died (1 from BP, 1 from cerebral hemorrhage, 2 from unavailable cause), 15 (5.7%) were lost to follow-up and 245 (92.8%) are still alive and currently followed at our Institute. The 5-year Overall Survival (OS) of the entire cohort was 96.2% (IC95% 92.2 - 100), without differences between the two groups [96.3% (95% CI 92.0 - 100) in the G-A versus 96.7% (IC95% 91.7 - 100) in the G-B; p=0.898].
Our data indicate a substantial homogeneity among ET patients regardless of the PLT number at diagnosis, thus confirming the usefulness of 2008/2016 WHO diagnostic criteria. Furthermore, the counterintuitive lower CIT observed in G-A, due to a larger use of cytostatic treatments and/or to an acquired Von Willebrand phenomenon when PLT levels > 1.000 x 109/l, highlights how thrombotic risk is unrelated to PLT value and leads to consider the administration of adequate cytostatic therapy even in patients with relatively lower PLT count at diagnosis.
Breccia:Novartis: Honoraria; Pfizer: Honoraria; Incyte: Honoraria; BMS: Honoraria. Foà:INCYTE: Other: ADVISORY BOARD; JANSSEN: Other: ADVISORY BOARD, Speakers Bureau; GILEAD: Speakers Bureau; CELTRION: Other: ADVISORY BOARD; ABBVIE: Other: ADVISORY BOARD, Speakers Bureau; CELGENE: Other: ADVISORY BOARD, Speakers Bureau; AMGEN: Other: ADVISORY BOARD; ROCHE: Other: ADVISORY BOARD, Speakers Bureau; NOVARTIS: Speakers Bureau.
