In this work, we evaluated the efficacy of Rigosertib and the expression of p53 in five different human tumor cell lines in vitro, A549 (lung adenocarcinoma), MCF-7 and MDA-MB231 (breast cancer cells), RPMI 8226 (multiple myeloma), and U87-MG (glioblastoma). The gene discussed is TP53; the disease is breast carcinoma.