In the present work, we evaluated the in vitro anticancer properties of some particular oxazolidinone derivatives, which are 5-(carbamoylmethylene)-oxazolidin-2-ones (OA-OI) shown in Scheme 1, against estrogen receptor-positive (ER+) breast cancer (MCF-7) and uterin cervix adenocarcinoma (HeLa) cell lines. This evidence concerns the gene ESR1 and breast cancer.