Paraneoplastic leukemoid reaction in a patient with BRAF V600E-mutated metastatic malignant melanoma.

A paraneoplastic leukemoid reaction is a rare condition of extreme leucocytosis in patients with solid malignancies. The differential diagnosis is often a true challenge. We present a case of a 56-year old woman with a history of stage IIIA malignant melanoma resected in 2004 that was diagnosed in May 2013 with BRAF V600E-mutated metastatic disease (left arm mass, lungs and adrenal glands). The laboratory findings revealed leucocytosis with granulocytosis that increased progressively to values up to 120.0 × 10(9)/L. After a diagnostic work-up, a diagnosis of a paraneoplastic leukemoid reaction was established. We report the response of leucocytosis to radiation and BRAF inhibitor therapy, albeit short-lived. To the best of our knowledge, this is the first case report of a paraneoplastic leukemoid reaction in metastatic melanoma with characterisation of BRAF V600 mutation status. It remains unclear whether the aggressive tumour phenotype is related to the leukemoid reaction and whether this is related to the BRAF mutation. 2015 BMJ Publishing Group Ltd.