In two different tumor lines with similar, low Trop-2 expression levels, the less SG-sensitive cell line (MDA-MB-231) readily up-regulated Rad51 in response to SG exposure, while the SG-sensitive cell line (SK-MES-1) was defective in HRR, as demonstrated by the lack of Rad51 up-regulation. This evidence concerns the gene TACSTD2 and neoplasm.