Prospective study of biomarkers in squamous cell carcinoma of the anal canal (SCCAC) and their influence on treatment outcomes: Five-year long-term results

4053 Background: Chemoradiation (CRT) is a curative treatment for SCCAC. However, some patients (pts) present primary CRT resistance. As a rare tumor, there is a lack of prospective studies of prognostic factors in this setting. Methods: This prospective cohort study was aimed to evaluate predictive biomarkers (Ki-67, PD-L1, Human papillomavirus (HPV), HIV status, and tumor DNA mutations) in SCCAC. We published the 6 months (m) response rate (RR) of this cohort showing that HIV- were 5.7 times more likely to achieve response 6m post CRT (OR 5.72, CI 95% 2.5-13.0, P < 0.001). Now we report the long-term follow-up results of 5-year progression-free survival (PFS) and overall survival (OS). Eligible pts had T2-4/N0-3/M0 disease and were candidates to standard CRT. DNA mutations were analyzed by next-generation sequencing (NGS). HPV positivity was tested by PapilloCheck Test. KI-67 and PD-L1 were evaluated by immunohistochemistry. Results: 78 pts were recruited from Jan/2011 to Dec/2015. 75 were evaluable for PFS and OS. The median age was 57 years; 49 (65%) were stage III, and 9 (12%) were HIV+. HPV was evaluated in 67 and found in 47 (70.1%); HPV16 was the most common. PD-L1 was tested in 61; 10 (16.4%) had positive expression > 1%. Ki-67 was performed in 65, with a median of 50% (range 1-90%). The median follow up is 66m. 5-year PFS and OS rates were 63.3% (95% CI 51.2-73.2%) and 76.4% (95% CI 64.8-84.6%), respectively. In a multivariate analysis, age (HR 1.06, P = 0.022, IC 95% 1.01-1.11) and absence of complete response at 6m (HR 3.36, P = 0.007, IC 95% 1.39-8.09) was associated with inferior OS. The OS rate was 62.5% in HIV+ group (95% CI 22.9-86%) in comparison with 78% (95% CI 65.7-86.3%) among HIV- pts, although this difference was not statistically significant (P = 0.400). A tendency to inferior OS was observed among pts with p53 codon 72 polymorphism (HR 2.83, P = 0.181, 95% CI 0.61-13.02). Other tumor mutations, HPV, Ki-67 expression, and PD-L1 expression, were not associated with PFS and OS. Conclusions: HIV- pts were 5.7 times more likely to achieve response 6m post CRT. The absence of complete response at 6m was the main factor associated with poor 5-year OS. New strategies of follow up and complementary treatment should be studied in late responders and HIV+ pts to ensure the success of curative treatment. Clinical trial information: 36211 .