Are ET and PV Patients Two Similar Populations As Concern Thrombotic Risk Factors?

Thrombotic events are major complications in patients (pts) affected by Essential Thrombocytemia (ET) and Polycytemia Vera (PV). To compare thrombotic risk in these 2 groups, we evaluated retrospectively our database of 1249 ET and 623 PV pts diagnosed and followed in 11 hematological centers in the Latium region between 1/1980 and 12/2010: the diagnosis was done according to PVSG, WHO 2001 and 2008criteria based on the time of first observation. Baseline features of ET pts: 797F/452M,median age 62.9 yrs (range 19-96),median WBC count 8.8 x 10⁹/L (range 1.2-57.7), median PLT count 812 x 10⁹/L (range 457-3582), median Hb level 14.0 g/dl (range 6-20.5), JAK-2 ^V617F positivity 59.7% with a median allele burden of 19,6% (range 0.2- 99.9), spleen enlargement in 18.7% of pts, previous thrombosis223/1239 evaluable pts (17.9%) [arterial 176/223 (14.1%), venous 47/223 (3.8%)]. Baseline features of PV pts: 289F/334M, median age 63.0yrs (range 21-91), median WBC count 10.1 x 10⁹/L (range 3.5-37.6),  median PLT count 457 x 10⁹/L  (range 169-1790),  median Hb level 18.2 g/dl (range 10.5-24.8), JAK-2^V617F positivity 94.3% with a median allele burden of 59.1%  (range 0.3-99.9), spleen enlargement in 42% of patients, previous thrombosis 146/617 evaluable pts (23.7%)[arterial 114/617 (18.5%), venous 32/617 (5,2%)].in the ET cohort, after a median follow-up of 7.7 yrs, thrombotic complications were seen in 107/1141 evaluable pts (9.4%) [arterial60 (5.25%), venous 47 (4.11%)]; in the PV cohort, after a median follow-up of 8.5 yrs, thrombotic complications were seen in 107/623pts (17.2%) [arterial 67 (10.8%),venous 40 (6.4%)].All common risk factors for thrombosis were evaluated in multivariate analysis, searching the cut-off number for continuous variables with ROC curves. The significant variables at multivariate analysis for ET and PV pts are shown in the table; age, previous thromboses and spleen enlargement were risk factors in ET pts, while previous thromboses and JAK-2^V617Fallele burden were risk factors in PV pts. PLT count above ROC value seemed to be a protective factor in both cohorts. In conclusion, in contrast with the tendency to evaluate in a similar manner the thrombotic risk of PV and ET, data from our retrospective database showed that these 2 groups should be considered populations with different risk factors for thrombosis.

Putative prognostic factors			Polycythemia Vera			Essential Thrombocythemia
			HR	95% C.I.	p	HR	95% C.I.	p
Previous thromboses			2,31	1,13 – 4,74	0,02	1,87	1,08 -3,23	0,026
Age ≥ 60 y			1,54	0,79 – 2,99	0,21	1,90	1,18 – 3,06	0,009
JAK2V617F	PV: allelic burden ≥ 81% ET : pos		1,95	1,03 – 3,71	0,04	0,76	0,48 – 1,21	0,25
Plt count	PV ≥ 452.109/L ET ≥ 944.109/L		0,49	0,25 – 0,95	0,04	0,52	0,31 – 0,89	0,017
Spleen enlargement			0,67	0,34 -1,31	0,24	1,71	1,02 – 2,89	0,04
CV risk factors (at least 1)			0,92	0,41 – 2,03	0,83	0,87	0,51 – 1,49	0,62
WBC		PV ≥ 10,175.109/L ET ≥ 9,630.109/L	1,09	0,57 – 2,08	0,80	1,41	0,89 -2,26	0,15