Paraneoplastic Hyperleukocytosis Mimicking Hematologic Malignancy Revealing a Localized Lung Cancer.

Paraneoplastic leukemoid reaction is a challenging differential diagnosis when it presents at the time of diagnosis of cancer. Severe hyperleukocytosis with elevation of blood neutrophils and monocytes counts can evoke myeloid hematologic malignancies. We report the case of a patient who presented with blood and bone marrow features highly suggestive of chronic myelomonocytic leukemia. The diagnosis of primary lung sarcomatoid carcinoma was performed. Surgical removal of this tumor which will always remain the priority led to full normalization of blood cell count.