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J-C. Ianotto et al.
Global analyses of recurrence of thrombotic events are not available here since most of the data were published for entire groups and not for individuals. However, con- sidering only the case reports (n=25), we recorded ten patients with ET who experienced a thrombotic event before or at diagnosis and only one had a recurrence dur- ing the follow up (10%). Among PV cases (n=10), five patients were in the same situation and two of them had a new thrombotic event (40%). Since this only represents a small group there is a risk of bias in these data.
Interestingly, the overall ratio of arterial/venous events (r=0.2) demonstrates a clear predominance of venous events (84.2%). This situation was identical both before and after the diagnosis. Concerning the sites of the events, thromboses of the splanchnic territories were most fre- quent (75% of the venous events), with a large predomi- nance of Budd-Chiari syndrome (62.5% of all venous events). Again, this is very different from the situation in the adult population (Online Supplementary Table S2).
Hemorrhagic events
The number of hemorrhagic episodes seemed very low (1% before and 4.8% after the diagnosis in ET patients and 4% in both situations in PV patients). Importantly, the use of an antithrombotic drug did not seem to increase the risk of hemorrhage. The episodes described in the litera- ture were mostly minor events, but their localization was usually unknown.
Transformation
As one of the most significant complications of MPN, transformation into secondary myelofibrosis and/or acute myeloid leukemia is a major concern. Such transformation frequently provokes a deterioration of the Performance Status and the necessity to change treatment strategy (i.e., to use ruxolitinib, allogeneic transplantation or intensive chemotherapy). Reassuringly, transformation seemed unusual in very young patients with MPN, with only 2% of cases evolving into myelofibrosis and none transform- ing into acute myeloid leukemia. However, this and other information about complications during the follow-up should be interpreted carefully because of the relatively short median follow-up of the cohorts and the case reports (54 and 51.3 months for ET and PV patients, respectively).
Another malignancy and long-term sequelae of therapy
Interestingly, Cario and colleagues observed that three among 36 PV patients (8.3%) were diagnosed with their MPN after having been cured from acute leukemia (2 cases) or lymphoma (1 case).9 There are only two cohorts of patients for which the occurrence of solid cancers in the young ET and PV patients was reported, with only one case of kidney cancer observed (1/97 patients, 1%). There is no information or evidence about the potential implica- tions of previous chemotherapy or cytoreductive drugs on the occurrence of MPN or cancer, despite the possible risk
Table 2. Treatments and outcomes of very young patients with essential thrombocythemia or polycythemia vera.
Antithrombotic drugs, n (%) Not treated
Low dose aspirin Vitamin-K antagonists Subcutaneous heparin
Cytoreductive drugs, n (%) Not-treated Hydroxycarbamide Anagrelide
Interferon
Venesections
Ruxolitinib Busulfan/Melphalan/32P Allogeneic SCT Thrombo/Erythropheresis
Complications before diagnosis, n (%) Thrombosis
Hemorrhage
Complications after diagnosis, n (%) Thrombosis
Hemorrhage
Transformation, n (%) Total
Polycythemia vera Myelofibrosis Acute leukemia
Death (n/%) Follow-up (months)
Essential thrombocythemia
*203 (51.3) 104 (51.2) 88 (43.3) 11 (5.4) 7 (3.4)
*239 (60.3) 112 (46.9) 31 (13) 50 (20.9) 11 (4.6) 0
0
0
0
1 (0.4)
* 307 (77) 16 (4)
4 (1)
* 307 (77) 15 (3.8) 19 (4.8)
*264 (68.7) 7 (1.8)
0
7 (1.8)
0
0
54
Polycythemia vera
*59 (78.7) 37 (62.7) 19 (32) 7 (11.9) 6 (10.2)
* 62 (82.7) 6 (9.7) 16 (25.8) 0
6 (9.7) 28 (45.2) 1 (1.6)
7 (11.3) 3 (4.8)
4 (6.5)
*69 (92) 11 (14.7) 3 (4)
*69 (92) 7 (9.3) 3 (4)
*19 (25.3) 2 (2.7)
-
2 (2.7) 0
3 (4)
51.3
*indicates the number and percent of available data for each category of parameters.32P:radioactive phosphorus;SCT:stem cell transplantation
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