Multicentre Investigation of Prognostic Factors Incorporating p16 and Tumour Infiltrating Lymphocytes for Anal Cancer After Chemoradiotherapy

Aims: Anal squamous cell carcinomas (ASCC) are strongly associated with human papillomaviruses. Standard of care is chemoradiotherapy at uniform doses with no treatment stratification. Immunohistochemical staining for p16INK4A (p16), a surrogate for human papillomaviruses, is prognostic for outcomes. We investigated this alongside clinical-pathological factors, including tumour infiltrating lymphocyte (TIL) scores.

Materials and methods: Using an independent, multicentre cohort of 257 ASCC treated with chemoradiotherapy, pretreatment biopsies were stained and scored for p16 and TIL. Kaplan-Meier curves were derived for outcomes (disease-free survival [DFS], overall survival and cancer-specific survival), by stage, p16 and TIL scores and Log-rank tests were carried out to investigate prognostic effect. A multivariate analysis was carried out using Cox regression.

Results: Stage, sex, p16 and TILs were independently prognostic. Hazard ratios for death (overall survival) were 2.51 (95% confidence interval 1.36-4.63) for p16 negative versus p16 positive, 2.17 (1.34-3.5) for T3/4 versus T1/2, 2.42 (1.52-3.8) for males versus females and 3.30 (1.52-7.14) for TIL1 versus TIL3 (all P < 0.05).

Conclusions: We have refined prognostic factors in ASCC. p16 adds to stratification by stage with respect to DFS in early disease and overall survival/DFS in locally advanced cancers. Our data support the role of the host immune response in mediating outcomes. These factors will be prospectively evaluated in PLATO (ISRCTN88455282).