HPV-negative squamous cell carcinoma of the anal canal is unresponsive to standard treatment and frequently carries disruptive mutations in TP53

BACKGROUND: Human papillomavirus (HPV), p16 expression, and TP53 mutations are known prognostic factors in head and neck squamous cell carcinoma, but their role in squamous cell carcinoma of the anal canal (SCCAC) is less well established. The objective of this study was to determine the prognostic significance of tumour HPV status, p16 and p53 expression, and mutations in TP53 in patients with SCCAC receiving (chemo)radiotherapy. METHODS: Human papillomavirus DNA was determined using an INNO-LiPA-based assay in tumour tissue of 107 patients with locally advanced SCCAC. Patients were treated with radiotherapy, with or without concurrent chemotherapy consisting of a fluoropyrimidine and mitomycin C. Expression of p16 and p53 was determined using immunohistochemistry. Exons 2–11 of TP53 in tumour tissue were sequenced. RESULTS: DNA of high-risk HPV types was detected in 93 out of 107 tumours (87%), all of which overexpressed p16 (HPV+/p16+). Of 14 HPV-negative (HPV−) tumours (13%), 10 (9%) were p16-negative (HPV−/p16−) and 4 (4%) overexpressed p16 (HPV−/p16+). Patients with HPV−/p16− disease had inferior 3-year locoregional control (LRC) (15%) compared with patients with HPV+/p16+ tumours (82%, P<0.001) and HPV−/p16+ tumours (75%, P=0.078). Similarly, 3-year overall survival (OS) was 35% (HPV−/p16−) vs 87% (HPV+/p16+, P<0.001) and 75% (HPV−/p16+, P=0.219). Disruptive mutations in TP53 were found in 80% of HPV−/p16− tumours vs 6% of HPV+/p16+ tumours (P<0.001). In multivariate analysis, HPV−/p16− status was an independent predictor of inferior LRC and OS. CONCLUSIONS: HPV− tumours are frequently TP53 mutated. HPV−/p16− status is a strong predictor for reduced LRC and OS, and alternative treatment strategies for patients with HPV−/p16− disease need to be explored.