Then, we investigated the potential cytotoxic properties via oxidative stress of the natural product 7-hydroxy-3,4-dihydrocadalene and the semi-synthetic cadinanes derivatives 7-(phenylcarbamate)-3,4-dihydrocadalene and 7-(phenylcarbamate)-cadalene against breast cancer cells using (Z)-4-hydroxytamoxifen as a positive cytotoxic control since is a Selective Estrogen Receptor modulator (SERM) that has remained the antihormonal therapy of choice for the treatment of Estrogen Receptor (ER) positive breast cancer. This evidence concerns the gene ESR1 and breast carcinoma.