IRS4 protein was most highly expressed in four cell lines with high IRS4 mRNA levels, namely NCI-H720 (lung atypical carcinoid), DMS-114 (small cell lung carcinoma), HEK293AAV (HEK293 cells that contain adeno-associated virus) and HEK293T (HEK293 cells harbouring the SV40 virus T-antigen), though not the parental HEK293 cells (Fig. 1B). The gene discussed is IRS4; the disease is small cell lung carcinoma.