74MO Clinical outcomes for pelvic node-positive vulvar carcinoma in the PET and IMRT era: Reassessing the stage IVb designation

Abstract

Pelvic node-positive (PNP) vulvar carcinoma has historically had poor outcomes; 2-year DFS was 27% in GOG 37. Studies in this cohort were performed prior to widespread PET staging and intensity modulated radiotherapy (IMRT). We assessed clinical outcomes and prognostic factors in FIGO IVb patients in the PET and IMRT era, hypothesizing that PET staging and IMRT treatment may improve outcomes. Following IRB approval, we reviewed all patients with PNP vulvar squamous cell carcinoma (SCC) who received IMRT from 2012-2022. Patients treated palliatively were excluded. Eligible patients met stage IVb criteria and received simultaneous integrated boost (SIB) to radiologically positive lymph nodes (LN). Tumor size, grade, PET primary and LN SUVmax, largest LN size, LN anatomic location, p16 status, chemotherapy (CHT), and RT completion were recorded, as were survival (OS), disease free survival (DFS), local (LRFS)/regional (RRFS) recurrence and distant metastasis (DMFS). Patterns of recurrence and survival were examined via Kaplan Meier, with univariate analysis (UVA) via log-rank t-test. Multivariate analysis (MVA) was performed via Cox regression. 198 patients received RT for vulvar SCC, and 31 met inclusion criteria. Median follow up was 26 months (IQR 9-49) for patients completing RT (n=25) and 3 months (IQR 1-9) for patients not completing RT (n=6). 93.5% (n=29) had PET staging, with avid LN at external iliac (74.2%, n=23), common iliac (16.1%, n=5) and para-aortic (9.7%, n=3) echelons. RT was majority definitive/neoadjuvant (83.9%, n=26); 93.5% (n=29) received concurrent CHT. 22.5% (n=7) underwent LN dissection, with median 3 LN resected and 2 LN positive. With RT completion, 3-year OS and DFS were 64.1% and 69.6%, with 82.6% LRFS, 83.1% RRFS, and 77.5% DMFS. On UVA, LN SUVmax correlated with worse DFS, RRFS, and DMFS, and p16- status with worse OS, RRFS, and DMFS (p<0.05). LN SUVmax retained significance for DFS (p=0.045) and DMFS (p=0.041) on MVA. Clinical outcomes for PNP vulvar SCC have substantially improved in the PET and IMRT era, challenging the FIGO IVb designation. PET LN SUVmax may help predict patients at higher risk of DM, and p16+ status those with more favorable outcomes.