Profound neutrophilia as the presenting sign of GCSF-secreting, ROS1-mutant squamous cell lung cancer

This is a case of squamous cell cancer (SCC) of the lung masquerading as a haematologic malignancy with marked neutrophilia ultimately found to have a <i>ROS1</i> rearrangement in a non-smoker patient. The patient achieved a near complete response to therapy and prompt resolution of neutrophilia after being started on a c-ros oncogene 1 (ROS1)-targeted tyrosine kinase inhibitor. Profound neutrophilia can be a presenting sign of granulocyte colony-stimulating factor (G-CSF) secreting SCC of the lung. This is significant because G-CSF can potentially masquerade as alternative diagnoses, delaying appropriate treatment. Neutrophilia may also be a potential tool for disease monitoring in such cases. Furthermore, this case describes a rare presentation of a ROS1 alteration in SCC of the lung. This illustrates the importance of routine comprehensive genomic profiling in lung cancer patients regardless of histology and smoking status.