Being the major cellular component of highly dynamic tissue endometrial stromal cells (EnSC) are exposed to cycles of proliferation upon hormonal stimulation what might pose risks for mutations accumulation and malignization. However, endometrial stromal tumors are rare and unusual types of tumor. The present study aimed to uncover defense mechanisms that might underlie resistance of EnSC against oncogenic transformation. All experiments were performed in vitro using the following methods: FACS, WB, RT-PCR, IF, molecular cloning, lentiviral transduction, and CRISPR/Cas9 genome editing. We revealed that expression of the mutant HRASG12V results in senescence of EnSC. We experimentally confirmed inability of HRASG12V-expressing EnSC to bypass senescence and resume proliferation even upon oestrogen stimulation. At the molecular level, induction of oncogene-induced senescence (OIS) was accompanied by the activation of MEK/ERK, PI3K/AKT, p53/p21WAF/CIP/Rb and p38/p16INK4a/Rb pathways, however inhibiting either pathway did not prevent cell cycle arrest. PTEN loss was established as the additional feature of HRASG12V-induced senescence of EnSC. By using CRISPR-Cas9 mediated PTEN knockout, we distinguished PTEN loss-induced senescence as a reserve molecular mechanism to prevent transformation of HRASG12V-expressing EnSC. The present study highlights oncogene-induced senescence as an antitumor defense mechanism of EnSC controlled by multiple backup molecular pathways.