Human papillomavirus (HPV) positive head and neck squamous cell cancers (HNSCC) are often characterized by low tumour (T) and high regional node (N) stages, indicating a high lymphatic metastatic potential. Although the dissemination pattern is different, the haematogenous metastatic rate is the same for HPV-positive and HPV-negative HNSCC. The biological mechanism behind this paradoxal dissemination pattern remains largely unknown.
We assessed the dissemination pattern in HPV-positive HNSCC combining data of 241 patients with in vitro and in vivo models. More specific, the effect of p16 and HPV on metastasis was assessed by invasion and migration assays. In vivo we focussed on angiogenesis (CD31) and lymphangiogenesis (LYVE-1).
Our study cohort confirmed that HPV-positive patients have significantly lower T stages and higher nodal involvement. HPV-positive cells had significantly lower migration rates and invasion capacities compared to HPV-negative cells. Downregulation of p16 increased migration and invasion capacities. To unravel the metastasis process, we focussed on angiogenesis and lymphangiogenesis, which are indispensable for oxygen and nutrient supply for tumour growth. A negative correlation between HPV and VEGFA was seen in the patient cohort and trend to significance was noted between p16 and VEGFA. Suppression of p16 increased the tumour vascularization. Secondly, HPV-positive tumours showed higher number of lymphatic vessels compared to HPV-negative tumours. P16 suppression in HPV-positive models resulted in lower lymphatic vessel density. This can be related to the α4β1 integrin, an important regulator of lymphangiogenesis, as HPV-negative tumours showed high percentages of this integrin.
These results suggest that p16 inhibits growth and invasiveness through inhibition of angiogenesis but also stimulates local spread by lymphatic vessel formation. This offers therapeutic applications for metastasis in HNSCC by inhibiting lymphangiogenesis in HPV-positive cancers and angiogenesis in HPV-negative cancers.