Extreme leucocytosis and splenomegaly in metastasised melanoma

A 63-year-old woman presented to the internist with fatigue, cough, low-grade fever, splenomegaly and leucocytosis up to 130 x 10(9)/l. Although a diagnosis of chronic myelogenous leukaemia was initially entertained, she turned out to have a metastasised melanoma. The differential diagnosis and workup is discussed, as well as potential mechanisms by which the tumour could have induced the leucocytosis, such as the production of G-CSF or similar mediators, and the prognostic significance of this phenomenon.