Patients with Unexplained Thrombosis Require a Prompt Investigation to Search a Chronic Myeloproliferative Neoplasm (MPN), Even If Platelet Count Is <600x10⁹/L. Analysis on 129 Patients from Registro Italiano Trombocitemie (RIT)

Background

In patients with Ph-negative MPN, a prior thrombosis (PrTh) occurs in around 1/5 of cases, with variable platelet (PLT) count and variable distance from diagnosis.

Objective

To investigate the influence of PLT count at PrTh on diagnostic and therapeutic approach in MPN patients.

Material and methods

We evaluated 129 MPN patients from RIT, reclassified according to WHO 2008 criteria as ET (n70), initial-primary myelofibrosis (n29), early-PV (n10), and unclassifiable-MPN (n20).

Results

Patients, 60 males and 69 females, showed following PrTh: 91(71%) major arterial (37 AMI, 4 angina, 24 stroke, and 26 TIA); 12(9%) minor arterial; 22(17%) major venous (8 DVT, 7 splanchnic, 4 cerebral sinus, 3 pulmonary embolism); and 4(3%) minor venous events.

PrTh occurred at a median distance of 4.1 months (range 0.1-118) from MPN diagnosis. This distance was >24 months in 21(16%) patients.

At occurrence of PrTh, median age was 58 years. PLT count (x10⁹/L) had a median value of 661 (range 150-2200), and was ≤450, 451-600, 601-700, 701-1000, and >1000 in 15(12%), 35(27%), 26(20%), 43(33%), and 10(8%) patients, respectively. Median white blood cell (WBC) count was 9.0 x 10⁹/L and median hematocrit (HCT) value was 46% in males, and 41% in females.

Median time (months) from PrTh to diagnosis of MPN was higher (p0.004) in patients with lower PLT count (x 10⁹/L): ≤450 (50.2), 451-600 (11.7), 601-700 (2.7), 701-1000 (1.8), and >1000 (1.4).

After occurrence of PrTh, all patients received conventional anti-thrombotic treatment, but in 7(5.4%) patients 9 recurrent thrombosis were reported before MPN diagnosis (11/100 pt-years).

At MPN diagnosis, clonality was documented in 101(78%) patients (JAK2 V617F mutation in 96 cases, 74%). The age was >60 years in 61(47%) patients. PLT count (x10⁹/L) had a median value of 720 (166-2440), and was ≤450 (n 7, 5%), 451-600 (n 21, 16%), 601-700 (n 28, 22%), 701-1000 (n 58, 45%), >1000 (n15, 12%). WBC count (10⁹/L) had a median value of 8.9, and was >10 in 40 (31%) cases. Median HCT level (%) was 45.6 in males and 42.1 in females. Cardiovascular risk factors (CVRF), comorbidities and symptoms were documented in 103(80%), 97(75%), and 57(44%) cases, respectively. Thrombotic risk (IPSET-Th) was high in 97.5%, and intermediate in 2.5% of cases. All 129 patients received anti-thrombotic drugs (low dose aspirin in 95% of cases) and, immediately after the diagnosis, they started a cytoreductive treatment (hydroxycarbamide 89%, anagrelide 8%, interferon-alpha 3%).

Patients with a PLT count (x10⁹/L) at PrTh ≤600(n 50), as compared with those with a PLT count >600(n 79), showed a longer median time to the MPN diagnosis (16.7 vs 2.0 months, p<0.001). No significant difference was found in the rate of: arterial PrTh (80% vs 79.7%, p0.97); recurrence of thrombosis before the diagnosis (8% vs 4%, p0.69); JAK2 V617F mutation (80% vs 71%, p0.29); age >60 years (52% vs 44%, p0.39); CVRF (82%vs79%, p0.63); WBC >10 x10⁹/L (23% vs 39%, p0.07); HCT high level [>47% in males, >44% in females](28% vs 36%, p0.37), and high thrombotic risk [IPSET-Th] (96%vs99%, p0.56). During follow-up (median 7.9 years) they showed a higher incidence of thrombosis recurrence (30%vs15%, p0.04; 4.5 vs 1.7/100 pt-y, p<0.01)

Conclusion

Time to MPN diagnosis was significantly longer in patients with PLT count (x10⁹/L) at PrTh ≤600 vs >600, and this time to diagnosis was characterized by a not negligible thrombosis recurrence. Moreover, during follow-up they showed a higher incidence of thrombosis recurrence.

This analysis strongly suggests that a PLT count <600 or even <450 x10⁹/L, in patients with unexplained thrombosis, deserves the search of a probable MPN, in order to promptly start cytoreductive treatment in addition to a conventional anti-thrombotic therapy.