Background: Platinum sensitivity (PS) is a prerequisite for first-line PARP inhibitors (PARPi) in locally advanced and relapsed high grade serous ovarian cancer (HGS-OC). BRCA mutations are predictive of PS and of response to PARPi. Notably, platinum and PARPi cytotoxic action is mainly related to p53-mediated inducted apoptosis. Therefore, the integrity of p53 machinery is crucial for platinum-related activity whereas the presence of p53 mutation is a fairly frequent event in ovarian cancer, especially in HGS-OC and in BRCA mutated. Methods: We prospectively analyzed 208 women with primary ovarian cancer undergoing surgery at the Department of Gynecologic Oncology, ARNAS G. Brotzu, Cagliari, Italy, between 2019 and 2023. Somatic NGS analysis was performed to detect BRCA and HRD mutations. TP53 mutations were classified according to according to hotspot, structural (missense/nonsense) and functional classification as “gain of function” (GOF) or “loss of function” (LOF), based on IARC TP53 database. Comparative testing with Fisher's exact test was used to examine TP53 mutation distribution and associations with clinicopathologic factors and PS. BRCA mutation status was further used to stratify the analysis. Results: Globally, we included 127 adult HGS-OC patients (pts). 84.2% had stage III-IV disease. TP53 mutation was found in 83.4% of pts. Somatic BRCA mutations were found in 28.3%. HGS-OC with somatic BRCA mutations had higher TP53 mutation frequency (88.8%) than BRCA WT (81.3%, p=0.1510). Employing the structural classification scheme, most harbored a missense TP53 mutation (76.5%). LOF TP53 mutations were found in 59.4% while GOF in 31.2%. No significant disparity was observed in the distribution of specific TP53 mutations within each classification scheme between cases with BRCA mutations and those without. As for BRCA mutated pts, TP53 WT were all PS. Among those p53 mutated, GOF mutations were associated with PS in 7 pts and platinum resistance in 3 pts; LOF mutations were associated with PS in 7 pts and platinum resistance in 12 pts. The difference in distribution of PS between functional categories of p53 mutations was significant (p=0.0291). As for BRCA WT pts, TP53 WT were all PS. Among TP53 mutated, GOF mutations were associated with PS in 14 pts and platinum resistance in 10 pts, whereas LOF mutations were associated with PS in 19 pts and platinum resistance in 25 pts, even if these findings were not statistically significant (p=0.2357). Of relevance, in 5 cases where LOF mutations of p53 was associated with null HIC p53 expression, pts were refractory to platinum-based chemotherapy. Conclusions: Even if preliminary, our data show that HGS-OC harboring TP53 null mutations are the poorest prognostic subgroup, especially in terms of PS. Further studies are needed to confirm our findings and the role of TP53 mutation as a biomarker of inherent or acquired platinum resistance.