O011/#287 Prognostic significance of ‘p53 signature’ (fields of dysplasia) and in situ margin status in organ-confined HPV-independent p53 abnormal vulvar squamous cell carcinoma

ObjectivesVulvar squamous cell carcinomas (VSCCs) can be stratified by HPV and TP53 mutation status to prognostically significant risk groups using p16 and p53 IHC. Treatment guidelines do not address optimal management of high molecular risk (TP53 mutated) pre-invasive neoplasia found at resection margins. Herein, we used p53 IHC to evaluate margin status in a retrospective cohort of HPV-independent (HPV-I) p53abn VSCCs.MethodsSurgically staged I-II HPV-I p53abn VSCCs from a single institution underwent margin (re)assessment using p53 IHC. Cases were segregated to i) morphologic dVIN at margin ii) vulvar skin with abnormal p53 IHC staining at margin and subtle morphologic features insufficient for dVIN iii) margins clear by morphology & p53 IHC TP53 mutation status was evaluated by next-generation sequencing (group ii). Clinicopathologic and outcome data was collated using a standardized collection tool.Results57 HPV-I p53abn VSCCs, FIGO stage I-II, were evaluated (Table 1). TP53 mutations were identified in 10/11 cases with subtle morphologic abnormalities insufficient for dVIN diagnosis and p53abn IHC extending to margins (synonymous with p53 signature). Positive in situ margins (dVIN and p53 signature) were observed in 27 (47.4%) of cases and significantly associated with disease recurrence (p=0.006).ConclusionsThese findings demonstrate: • p53abn IHC staining at margins, without sufficient morphologic features for dVIN diagnosis, predicts an equivalent or higher recurrence risk compared to morphologic dVIN • p53 IHC is critical for accurate assessment of margin status in HPV-I p53abn VSCC • The need to evaluate biologically-informed treatment approaches for high molecular risk (TP53 mutated) disease in prospective interventional studies