Background: Human papillomavirus (HPV) is the major predictor of outcome in oropharyngeal squamous cell carcinoma (OSCC) but the disease is heterogeneous and there is limited understanding of the prognostic significance of other molecular markers in relation to HPV. This multi-institutional, retrospective study examined the prognostic significance of Ki67 expression in association with HPV status in OSCC.
Methods: The 105 patients recruited had a median follow-up of 70 months. Tumor HPV status was determined by HPV E6-targeted multiplex real-time polymerase chain reaction/p16 semiquantitative immunohistochemistry and Ki67 expression by semiquantitative immunohistochemistry. Determinants of recurrence and mortality hazards were modelled using Cox regression with censoring at dates of last follow-up.
Results: HPV and Ki67 positivity rates were 46 and 44 %, respectively. HPV-positive cancers were more likely to be Ki67-positive. On multivariate analysis, both HPV and Ki67 were predictors of outcome. Ki67-positive cancers were associated with a 3.13-fold increased risk of disease-related death compared with Ki67-negative cancers. Among HPV-negative patients, Ki67-positive disease was associated with 5.6-fold increased risk of oropharyngeal cancer-related death (p = 0.002), 5.5-fold increased risk of death from any cause (p = 0.001), and 2.9-fold increased risk of any event (p = 0.013). The risk of locoregional failure was lowest in patients with HPV-positive/Ki67-positive cancers.
Conclusions: Ki67 predicts disease-related death in oropharyngeal cancer independent of HPV status. A combination of Ki67 and HPV status provides improved prognostic information relative to HPV status alone. Our data suggest, for the first time, that Ki67 status has prognostic value, particularly in HPV-negative oropharyngeal cancer.