P27 and mib1 expression in actinic keratosis, Bowen disease, and squamous cell carcinoma.

The histologic boundary between actinic keratosis, Bowen disease, and invasive squamous cell carcinoma is not clear in many cases. We determined nuclear expression of p27 (a protein associated with cellular quiescence) and Ki-67 (a marker of proliferation) immunohistochemically in actinic keratosis, Bowen disease, and squamous cell carcinoma to see if differential patterns of expression for p27 exist and how these might correlate with Ki-67 expression. We determined a labeling index for p27-stained nuclei and assessed the pattern of Ki-67 expression. The student's t test was used to evaluate the p27 labeling index. The p27 labeling index was decreased in invasive aggregates of squamous cell carcinoma (76.9+/- 1.1%) when compared with those of normal epidermis (97.2+/- 2.4%), actinic keratosis (95.3 +/- 1.4%), and Bowen disease (98.0+/- 0.5%). Ki-67 was expressed in a scattered to confluent linear pattern in the basal/parabasal cell layer of normal epidermis and actinic keratosis. Keratinocytes in squamous cell carcinoma exhibited Ki-67 in the peripheral layers of the neoplasm and frequently within the tumor aggregates. Ki-67 was observed in nuclei throughout the full thickness of the epidermis in Bowen disease. The staining pattern of Ki-67 in Bowen disease separated this entity from others under study. The combination pattern of p27 and Ki-67 staining can be used to support differentiation of actinic keratosis, Bowen disease, and squamous cell carcinoma.