CDKN2A and cervical carcinoma: Furthermore, due to the limited size of the tumour biopsies, we could not assay for HPV E6 and E7 mRNA as marker for active HPV in tumour cells, instead we analysed for p16 INK4a, which has previously been used as a surrogate marker for HPV in cervical cancer [27] and HPV activity in head and neck cancer.