Cervical Adenoid Basal Carcinoma: Clinicopathologic Features of 9 Cases With Reference to CK17 and Ki-67 Expression.

Objective The aims of this study were to clarify the histological features of adenoid basal carcinoma (ABC) and determine whether cytokeratin 17 (CK17) and Ki-67 can facilitate the differential diagnosis of ABC from squamous cell carcinoma (SCC). Materials and Methods Nine cases of pure ABC were collected from the files of the Division of Pathology at the Zhejiang University Hospital Women's School of Medicine. For comparison, 20 cases of moderately to poorly differentiated cervical SCC, including 2 of basaloid SCC, were also retrieved from the same period. Blocks were recut, reread, and immunostained for CK17 and Ki-67. Results Morphologically, ABCs were mainly composed of small basaloid cell nests and variable squamous differentiation foci. For immunohistochemical staining, 1 of 9 cases showed diffuse CK17 staining, 5 of 9 showed focal positive staining, and 3 of 9 showed negative staining in the basaloid cell area of ABC, whereas no CK17 expression was found in ABC squamous foci. Eighteen of the 20 invasive SCCs showed diffuse CK17 staining, and 2 showed focal staining. The Ki-67 proliferative index varied in different ABC areas, with a relatively high index in squamous differentiation foci and a low index in basaloid cell areas. In contrast, Ki-67 staining was unevenly intense in SCC. Conclusions Adenoid basal carcinoma had characteristic morphological features, and the differential diagnosis of ABC from SCC is usually simple, based on morphology. In select cases, when histological findings are equivocal, the loss of CK17 expression in the squamous differentiation area, and a lower Ki-67 index in basal cell foci support ABC diagnosis.