As for DS-6157a, it is a conjugate of anti-GPR20 antibody and DNA topoisomerase I inhibitor exatecan derivative (DX-8951 derivative, DXd), which demonstrated strong cell killing activity against GIST in cell lines, cell line-derived xenograft (CDX) and PDX models [251, 252], and a phase I clinical trial examining the antitumor effect of DS-6157a in GIST patients is now ongoing [220]. Here, TOP1 is linked to gastrointestinal stromal tumor.