First-line carboplatin-paclitaxel (CP) for metastatic anal squamous cell carcinoma (ASCC): An analysis of dosing schedules.

e15501 Background: CP is the backbone of first-line therapy for recurrent or metastatic ASCC. In practice, Q3-week CP has been explored as a potential alternative to the standard (d1,8,15 Q28-day cycle) dosing, though its efficacy is not known. This study evaluated CP scheduling and clinical survival associations in metastatic ASCC. Methods: This multicenter retrospective cohort study included patients with metastatic ASCC treated with first-line CP, identified using the Mayo Data Explorer database. Electronic health records were reviewed to collect baseline clinical characteristics, treatment regimens, responses, progression-free survival (PFS), and overall survival (OS). Descriptive statistics were used to summarize patient demographics. Survival was estimated using Kaplan–Meier methods. Multivariable Cox proportional hazards models were used to compare survival by dosing schedule, adjusting for age, ECOG performance status, HPV (p16) status, liver metastasis, and prior chemoradiation. Results: 54 patients treated between 2020-2025 with first-line CP for metastatic ASCC were included. Baseline patient demographics were balanced between dosing groups (Table 1). Median follow-up time was 26.2 months. For Q3-week CP (n = 21), median PFS and OS were 9.8 (95% CI 8.1, NR) and 27.0 (95% CI 15.7, NR) months, respectively, while median PFS was 6.5 (95% CI 4.5,15.3) months with standard CP (n = 33) and median OS was not reached (95% CI 11.2, NR). Response rate was 76% with Q3-week and 60.6% with standard CP (p = 0.23) dosing. Survival outcomes were similar when comparing Q3-week CP relative to standard CP dosing using multivariable analysis (PFS HR 0.68, 95% CI 0.33–1.41; OS HR 1.67, 95% CI 0.67–4.14). Higher ECOG and liver metastasis were independently associated with inferior outcomes, while HPV was associated with improved survival. Subsequent therapy patterns were similar between CP schedule groups. Ten patients (16.9%) received local therapy, and 24 of 28 patients with progression received further systemic therapy, including 21 (87.5%) treated with immunotherapy. Conclusions: Survival outcomes were similar across dosing schedules, suggesting Q3-week CP may be a reasonable alternative to standard CP, with potential to reduce treatment-related burden in metastatic ASCC. Future analysis will compare toxicity profiles between CP dosing schedules, including in combination with PD1 inhibitors given the results of the POD1UM-303 trial. Patient demographics (n=54). Variable Q3-week CP (n=21) Standard CP (n=33) p-value Sex Female 16 (76.2%) 24 (72.7%) 0.77 Male 5 (23.8%) 9 (27.3%) Age Median (Q1, Q3) 62 (50.5, 69) 64 (55.5, 70) 0.57 BMI Median (Q1, Q3) 27.1 (21.9, 34.4) 27.4 (22.5, 31.7) 0.72 ECOG 0 9 (42.9%) 11 (34.4%) 0.53 ≥ 1 12 (57.1%) 21 (65.6%) Confirmed HPV (p16) Positive 16 (76.2%) 24 (72.7%) 0.77 Prior chemoradiation Yes 17 (81.0%) 21 (63.6%) 0.17