SCN9A and cancer: TTX shows very little selectivity across a number of Nav family members, with IC50 values for Nav1.1, 1.2, 1.3, 1.4, 1.6 and 1.7 being in the single nanomolar range.[38] Despite the lack of selectivity, TTX is currently undergoing phase III clinical trials for treatment in cancer-related pain, where it is administered subcutaneously to limit systemic effects.[81] Although the selectivity and therapeutic index of natural toxins may limit their therapeutic use, they hold promise as scaffolds for the development of more specific inhibitors targeting for example, Nav1.7.