SCN9A and cancer: In its primary form, it has been linked to an autosomal dominantmutation in the sodium voltage-gated channel alpha subunit 9 (SCN9A) gene.1 Secondary erythromelalgia occurs asa result of a multitude of conditions, including myeloproliferative disorders,connective tissue diseases, infections, and malignancy.2 We postulate that the etiology of erythromelalgiain our patient was secondary to polycythemia.