What is the cut off point for determining p16+ by immunohistochemistry regarding nuclear expression?

The cut-off point for determining p16 positivity by immunohistochemistry is indeed characterized by specific criteria regarding intensity and distribution. In the context of p16, which is a tumor suppressor protein commonly used as a biomarker in various cancers, the correct standard is having a staining intensity of +2 or +3, in combination with a distribution threshold of 75%.

The rationale behind this is that +2 or +3 intensity indicates a strong, significant expression of the p16 protein, which is often associated with the presence of high-risk Human Papillomavirus (HPV) types in cervical and other HPV-related cancers. The requirement for 75% distribution signifies that the expression must be widespread across a substantial portion of the tumor cells to be deemed significant for diagnostic purposes.

Using lesser intensity levels (like +1) or different distribution percentages would not meet the established criteria needed to reliably suggest that a tumor is p16 positive and thus may not reflect the same level of association with HPV oncogenic processes. The stringent requirements help ensure that the diagnosis based on immunohistochemistry is robust and clinically relevant.