A case of paraneoplastic hyperleukocytosis closely mimicking chronic neutrophilic leukemia

Leukemoid reaction and myeloproliferative syndrome are close mimickers and frequently pose a diagnostic dilemma, particularly when the leukocyte count is very high. Leukocyte alkaline phosphatase score frequently aids in diagnosis but may or may not be contributory, especially in differentiating chronic neutrophilic leukemia. Herein, we document a case of leukemoid reaction with extensive hyperleukocytosis in a 46-year-old female with poorly differentiated carcinoma. The tumor itself as well as the associated leukocytosis portends a poor prognosis.