- For oropharyngeal tumors p16 immunohistochemistry (IHC) positivity is sufficient to enroll and initiate treatment (p16 IHC interpretation to follow guidelines by Jordan/Lingen et al 2012); it is recommended that p16 IHC positivity is validated at a later point (during or after treatment) using an E6/E7 based test at the University of Chicago and provided slides will be used