Kaplan-Meier estimate of survival in primary myelofibrosis according to DIPSS. Risk factors and corresponding score values are as following: age greater than 65 years (1 point), presence of constitutional symptoms (1 point), hemoglobin level below 10 g/dL (2 points), leukocyte count greater than 25 ×10⁹/L (1 point), and circulating blast cells 1% or greater (1 point). Risk categories are defined according to the sum of points obtained anytime during follow-up. Low risk: score 0, intermediate-1 risk: score 1–2; intermediate-2 risk: score 3–4, and high risk: score 5–6.