To further investigate the reverse causality, we next performed bidirectional MR analysis for seven potential plasma proteins in the primary analysis (genetic instruments shown in Supplementary Table S3), which suggests that SCLC caused significant changes in plasma levels of nearly all of them based on MR-IVW, except SHMT1 and CTSB, which had opposite changes between MR-IVW and other methods (Supplementary Figure S1). Here, SHMT1 is linked to small cell lung carcinoma.