Background: To the authors' knowledge, the literature regarding extreme leukocytosis in solid tumor patients is sparse, consisting of a few case reports and small case series.
Methods: A total of 3770 consecutive solid tumor patients with a white blood cell count>40,000/microL were retrospectively identified over a 3-year period (2005-2008). Those patients without a secondary cause of their leukocytosis were defined as having a paraneoplastic leukemoid reaction.
Results: A total of 758 (20%) patients with solid tumors and extreme leukocytosis were identified. The etiology of the leukocytosis was hematopoietic growth factors in 522 (69%) patients, infection in 112 (15%) patients, high-dose corticosteroids in 38 (5%) patients, newly diagnosed leukemia in 9 (1%) patients, and paraneoplastic leukemoid reaction in 77 (10%) patients. The patients diagnosed with a paraneoplastic leukemoid reaction typically had neutrophil predominance (96%) and radiographic evidence of metastatic disease (78%), were clinically stable, and had a poor prognosis; 78% either died or were discharged to hospice within 12 weeks of their initial extreme leukocyte count. All of the 8 (10%) patients who survived>1 year received effective antineoplastic therapy.
Conclusions: Infection was an uncommon cause of extreme leukocytosis in patients with solid tumors. Patients with paraneoplastic leukemoid reactions typically were clinically stable despite having large tumor burdens. However, clinical outcomes were poor unless effective antineoplastic treatment was received.