- Immunohistochemical staining for p16 must be performed on tissue, and this tissue must be submitted for central review; fine needle aspiration (FNA) biopsy specimens may be used as the sole diagnostic tissue if formalin-fixed paraffin-embedded cell block material is available for p16 immunohistochemistry; FNA specimens prepared with adequate p16 testing in this manner are acceptable to submit for central review; if the p16 preparation is not adequate, additional specimens will be required to establish p16 status; centers are encouraged to contact the pathology chairs for clarification