Introduction/Background The prevalence of occult invasive malignancy in biopsy proven VIN3/dVIN has been suggest to be between 9–22%. Traditionally precancerous vulval lesions have been treated with a wide local excision which can significantly alter the vulval anatomy

Aim To determine the prevalence of invasive cancer in biopsy proven VIN3/dVIN. To determine whether clinical suspicion (or not) of invasion in lesions where the biopsy shows precancerous lesion changes can help tailor management allowing less radical treatment.

Methodology Retrospective study of all patients at the Royal Derby Hospital from 2009–2018 who received wide local excision or skinning vulvectomy (WLE/SV) for a biopsy proven VIN3 or dVIN lesion within 6 months from initial diagnosis. Patient, surgeon and pathological data was recorded.

Results 86 patients were identified. 71 patients were diagnosed with VIN3 at the initial biopsy of which 7(9.8%) showed invasive cancer after WLE/SV. When subgrouped by clinical suspicion (if recorded) 4/11 (36%) suspicious VIN3+ve lesions showed cancer compared to 2/46 (4.3%) that did not. Overall the PPV and NPV for clinical assessment in biopsy proven VIN3 was 36% and 96% respectively.

15 patients were diagnosed with dVIN, of which 6 (40%) demonstrated cancer after WLE/SV. Clinical suspicious was recorded in five cases of which four (80%) ultimately had a cancer after WLE/SV. The PPV and NPV for clinical suspicion of invasion in dVIN was therefore 80% and 78% respectively

Conclusion Prevalence of occult carcinoma in biopsy proven VIN3 and dVIN is 9.8% and 40% respectively in this cohort. Clinical suspicion at the time of biopsy alters the subsequent risk of malignancy and may allow less radical surgery in selected women with VIN3 with no clinical suspicion of invasion

Disclosure Nothing to disclose