EP658 - What determines survival in anal cancer? A 10-Year retrospective cohort study

Purpose/Background: Anal squamous cell carcinoma is a rare malignancy with a steadily rising incidence, mainly associated with human papillomavirus (HPV) and human immunodeficiency virus (HIV) infection. Concurrent chemoradiotherapy (CRT) remains the standard of care, offering high sphincter-preservation and local control rates. Nevertheless, survival outcomes depend strongly on tumor stage and treatment response. This study aimed to identify prognostic factors associated with overall survival (OS) in a Mexican cohort with long-term follow-up.

Aim: To identify clinical and therapeutic factors associated with overall survival in patients with anal squamous cell carcinoma treated over a 10-year period.

Methods/Interventions: A retrospective observational study was conducted including 123 patients diagnosed with anal squamous cell carcinoma between 2015 and 2025. Clinical, pathological, and therapeutic variables were analyzed. OS was defined as the time from diagnosis to death from any cause or last follow-up. Kaplan-Meier survival curves were generated, and differences were assessed using the log-rank test, with p< 0.05 considered statistically significant.

Results/Outcomes: The mean overall survival (OS) was 42.6 months, and the median was 29 months. Males accounted for 56.6 % (mean age 51.6 years). HPV infection was present in 97 % of cases and HIV in 42.6 %. The predominant stage was IIB (36.9 %), followed by IIIC and IV (22.1 % each). CRT was administered to 76.2 % of patients, achieving a complete response (CR) in 58.2 %. Patients with CR had significantly longer OS (56.5 months) compared with those without CR (17.3 months; p< 0.001). CRT yielded superior OS compared with palliative chemotherapy (49.6 vs 9.7 months; p< 0.001). Tumor progression and recurrence markedly reduced OS (11.2 and 16.6 months, respectively; p< 0.001). Advanced clinical stages correlated with poorer prognosis, confirming the predictive value of TNM classification. Radical surgery did not improve OS and was associated with higher morbidity and mortality.

A trend toward better OS was observed in female and HIV-negative patients, although differences were not statistically significant. The 3-year OS exceeded 80 % in those achieving CR, compared with < 30 % among non-responders. Progression was the strongest negative predictor (HR 5.8, 95 % CI 3.2-10.4), followed by recurrence (HR 3.4, 95 % CI 1.8-6.5). Most deaths occurred within the first 24 months after diagnosis, emphasizing the importance of early tumor control. Among patients who failed CRT, 40 % underwent salvage surgery, achieving limited benefit in OS. Kaplan-Meier curves demonstrated clear separation between survival trajectories according to response and treatment modality (log-rank < 0.001). The survival plateau observed beyond 60 months in patients with CR supports the durable efficacy of concurrent CRT. Overall, these data highlight complete response as the cornerstone of long-term survival and reaffirm the critical role of early multidisciplinary intervention in optimizing outcomes.

Conclusion/Discussion: Complete response and chemoradiotherapy were the strongest favorable prognostic factors for overall survival. Conversely, progression, recurrence, and advanced stages were associated with increased mortality. These findings underscore the importance of early diagnosis, multidisciplinary treatment, and preventive strategies-including HPV vaccination and anal screening-in high-risk populations.

Figure 1. Kaplan-Meier overall survival curves according to clinical stage.
Overall survival by clinical stage in patients with anal squamous cell carcinoma. The median overall survival decreased progressively with advancing stage. Patients with Stage I and II disease showed excellent long-term survival, while those with Stage III and IV had significantly poorer outcomes. The log-rank test demonstrated a statistically significant difference among stages (p < 0.001).
Table 2. Overall survival according to tumor characteristics
Note: Data are presented as mean ± standard deviation. Comparisons between groups were performed using Student's t-test for independent samples. A p value < 0.05 was considered statistically significant.