A 65-year-old man presents to his primary care physician with a 2-month history of increasing fatigue, left upper quadrant discomfort, and a 7-lb unintentional weight loss. Complete blood count reveals a white blood cell (WBC) count of 123,000/µL with a left-shifted differential without any peripheral blasts; hemoglobin is 12.1 g/dL and platelets are elevated at 473 × 10³/µL. The spleen tip is palpated 3 cm below the left costal margin. A bone marrow biopsy is read as markedly hypercellular (95%) with trilineage hematopoiesis, no evidence of dysplasia, marked myeloid hyperplasia without any increase in blasts, and focal areas with 1+ reticulin fibrosis.