Clinical characteristics and treatment outcome in p16 negative anal cancer

Background: Anal squamous cell carcinoma (ASCC) is linked to human papillomavirus infection with p16 being positive in about 85% of cases. Overall survival (OS) of ASCC is 60%-80%. Prognosis in p16 negative (p16-) ASCC is worse with an OS of 30%-60%. It is important to elucidate differences in p16+ and p16-ASCC characteristics and outcome. Methods: Consecutive ASCC patients (n = 380) treated with curative intent in Uppsala 2017-2022 were reviewed and analyzed retrospectively. A cohort of p16-patients (n = 30) from Gothenburg was included as a validation cohort. Results: Ninety-one per cent (n = 347) were p16+ and 9% (n = 33) p16-. Median follow-up was 33 months (range 4-78). p16-status was associated with higher age (>= 65 years; p = 0.03), comorbidity (p = 0.03), male sex (p = 0.001) and perianal localization (p < 0.001). At 3 years progression free survival was 50% and 81% (p <0.0001) and OS60% and 89% (p < 0.0001) for p16-and p16+ patients, respectively. Male sex, advanced T-stage (T3-4), N+ disease, advance treatment and p16-status were associated with inferior OS (p = 0.01-p < 0.0001). In the p16-subgroup, advanced T-stage and intensive treatment were negative prognostic factors for OS (p = 0.007 and 0.009, respectively) but no clinical characteristic predicted persistent disease. The p16-validation cohort essentially confirmed the findings from the main cohort. Interpretation: p16-ASCC is a disease subset with specific clinical features and poor prognosis in need of improved treatment.