Different types of cervical cell staining with the p16INK4a-specific antibodies. a. Normal epithelium (smear): negative staining. b. CIN I (indicated with a dotted arrow) and cancer in situ (solid arrows): a very poor cytoplasmic staining in separate CIN I cells and sporadic staining in cancer in situ. c. Invasive squamous cell carcinoma. Diffuse cytoplasmic staining with the sole cell expressing p16INK4a in the nucleus (solid arrow). The boundary with adjoining normal tissue is marked with a dotted arrow. d. HT3 cells (smear) with both nuclear and cytoplasmic subcellular location of the positive staining.