<b>Results:</b> ES-SCLC patients harbored higher percentages of CD8<sup>+</sup> Teffs (<i>p</i> = 0.005) and FOXP3<sup>+</sup> Tregs (<i>p</i> < 0.0001) in circulation before therapy compared with healthy donors. This evidence concerns the gene CD8A and small cell lung carcinoma.