Leukemoid reaction causing arterial thrombus in a patient with lung adenocarcinoma

A leukemoid reaction is typically defined as white blood cell (WBC) count >50×10⁹/L, predominantly neutrophil precursors, that are not due to tumour involvement in the bone marrow and not derived from clones. Leukemoid reactions associated with malignancy, known as paraneoplastic leukemoid reactions, are less common and are most notably seen with non-small cell lung cancer. A 64-year-old woman presented with right leg painful ulceration. On examination, she had multiple venous stasis ulcers more severe on the right, with no palpable pulses in her lower extremities. Her WBC count was 124×10⁹/L and platelets were 517×10⁹/L. Arterial dopplers showed limb-threatening arterial insufficiency which prompted right femoral endarterectomy. Few months earlier she was diagnosed with metastatic lung adenocarcinoma to the bone and she had leukemoid reaction with WBC 43.920× 10⁹/L with 90% neutrophils. Repeat imaging showed progression of her malignancy and she passed shortly after. Inflammation is a key element of carcinogenesis and cancer progression. Among the different tumours, lung cancer is a non-haematologic malignancy that is most closely associated with leucocytosis. Some studies have found that leucocytosis was significantly associated with metastasis and shorter survival irrespective of other factors such as age or sex. The mechanism remains unclear however elevated levels of granulocyte colony-stimulating factor (CSF), granulocyte macrophage-CSF and interleukin 6 have been linked to this phenomena. The degree of leucocytosis seen in our patient is suggestive of CSF production leading to a paraneoplastic leukemoid reaction.