Of historical interest the tropism of SVV-001 for SCLC cells with low ASCL1 to NEUROD1 ratio was one of the initial observations that prompted further investigation into novel subtypes of SCLC, classified by expression of master transcriptomic regulators that are emerging as an important area of investigation and biomarkers of response to treatment. This evidence concerns the gene ASCL1 and small cell lung carcinoma.