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Polycythemia vera (PV) is a rare myeloproliferative neoplasm (MPN) associated with a high risk of vascular events and substantial disease burden that impair the quality of life of patients.1 Hydroxyurea has been the standard of care for PV for a long time, however, a proportion of patients with PV become resistant or are intolerant to hydroxyurea.2,3 There are only few promising first-line treatment alternatives which are mostly consisting of peginterferon alpha compounds (read more here). Nevertheless, together with the fact that in more than 95% of patients the underlying PV etiology is a mutation in the Janus kinase 2 (JAK2; V617P) gene, the JAK inhibitor, ruxolitinib, evolved as a very promising therapeutic target.2
In fact, the primary results from the RESPONSE phase III trial led to the approval of ruxolitinib by the U.S. Food and Drug Administration and European Medicines Agency for PV patients resistant or intolerant to hydroxyurea.3 The long-term efficacy and safety of ruxolitinib in this patient subset was investigated in a 5-year follow-up study of the RESPONSE phase III trial by Jean-Jacques Kiladjian and colleagues.2 The results of the study were published in the Lancet Haematology and are summarized below.
Table 1. Key efficacy and safety results at week 32 of the RESPONSE phase III trial2,3
*Primary composite endpoint, proportion of patients achieving both hematocrit control without phlebotomy and ≥ 35% reduction in spleen size at week 32 In bold, statistically significant values (p < 0.05) |
|||
Ruxolitinib (n = 110) |
Best available therapy (n = 112) |
p value |
|
---|---|---|---|
Patients achieving the primary endpoint* |
20.9% |
0.9% |
< 0.001 |
Patients achieving hematocrit control |
60.0% |
19.6% |
— |
Patients with ≥ 35% spleen size reduction |
38.2% |
0.9% |
— |
Complete hematological remission |
23.6% |
8.9% |
0.003 |
Table 2. Key efficacy results at week 256 of the 5-year follow-up of the RESPONSE phase III trial2
|
Ruxolitinib |
---|---|
Progressing after achieving the primary endpoint at week 32 |
24% |
Median duration of primary response |
Not reached |
Progressing after achieving hematocrit control at week 32 |
24% |
Maintaining hematocrit control (week 32 to week 224) |
73% (95% CI, 60–83) |
Progressing after achieving complete hematological remission at week 32 |
38% |
Maintaining complete hematological control (week 32 to week 224) |
55% (95% CI, 32–73) |
Maintaining at least a 35% reduction in spleen size (week 32 to week 224) |
72% (95% CI, 34–91) |
Progressing after achieving complete clinicohematological response at week 32 |
30% |
Maintaining complete clinicohematological response (week 32 to week 224) |
67% (95% CI, 54–77) |
Median duration of clinicohematological response |
Not reached |
Table 3. Most common all-grade hematological and non-hematological AE rates from the 5-year follow-up of the RESPONSE phase III trial2
AEs, adverse events *Exposure-adjusted rates ≥ 5 per 100 patient-years |
||||
|
Ruxolitinib |
Best available therapy |
Crossover group |
|
---|---|---|---|---|
Hematological AE rates* |
||||
Anemia
|
8.9 |
5.4 |
8.8 |
|
Thrombocytopenia |
4.4 |
16.3 |
1.2 |
|
Non-hematological AE rates* |
||||
Pruritus |
7.0 |
32.6 |
6.1 |
|
Diarrhea |
7.0 |
12.2 |
3.6 |
|
Weight gain |
6.1 |
1.4 |
4.2 |
|
Headache |
5.8 |
28.5 |
5.2 |
|
Arthralgia |
5.6 |
10.9 |
3.3 |
|
All infections Herpes zoster |
18.9 4.7 |
59.8 0.0 |
19.1 3.9 |
Table 4. Most common thromboembolic event rates from the 5-year follow-up of the RESPONSE phase III trial2
*Exposure-adjusted rates ≥ 5 per 100 patient-years $Other thromboembolic events include: for best available therapy, splenic infarction; and for the crossover group, bone infarction, disseminated intravascular coagulation and coronary artery occlusion |
||||
Ruxolitinib (n = 110) |
Best available therapy (n = 111) |
Crossover group (n = 98) |
||
---|---|---|---|---|
Thromboembolic event rates* |
||||
All events |
1.2 |
8.2 |
2.7 |
|
Cerebral infarction |
0.2 |
0 |
0 |
|
Ischemic stroke |
0.2 |
0 |
0.3 |
|
Pulmonary embolism |
0.2 |
1.4 |
0 |
|
Portal vein thrombosis |
0.2 |
0 |
0 |
|
Retinal vascular thrombosis |
0.2 |
0 |
0 |
|
Deep vein thrombosis |
0 |
2.7 |
0.3 |
|
Myocardial infarction |
0 |
0 |
0.6 |
|
Transient ischemic attack |
0 |
0 |
0.6 |
|
Thrombophlebitis |
0 |
1.4 |
0.3 |
|
Thrombosis |
0 |
1.4 |
0.3 |
|
Other$ |
0 |
1.4 |
0.9 |
The results from the 5-year follow-up of the RESPONSE phase III trial indicate that ruxolitinib continues to be superior to best available therapy (including interferons), with a substantial proportion of patients maintaining deep durable responses. Moreover, in the long term, ruxolitinib led to fewer thromboembolic events and lower rates of serious AEs, when compared to best available treatment. All these beneficial effects of ruxolitinib were also observed in the crossover patients despite having a shorter exposure to the treatment. In summary, these results provide strong evidence that ruxolitinib is a safe and effective long-term regimen for patients with PV who cannot be treated with hydroxyurea.
References
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