PAX2 and cyclin D1 expression in the distinction between cervical microglandular hyperplasia and endometrial microglandular-like carcinoma: a comparison with p16, vimentin, and Ki67.

Microglandular hyperplasia (MGH) is a common endocervical alteration that in most cases presents no diagnostic difficulty. However, MGH rarely shows atypical features that may mimic endocervical neoplasia, while conversely endometrial carcinomas can show deceptively bland MGH-like appearances. It has been suggested that immunohistochemical analysis is useful in this context, but relatively few studies have specifically investigated microglandular pattern lesions and the results have been conflicting. In this study, we have examined a series of MGH (n=24), atypical MGH (n=2), and endometrial microglandular-like carcinomas (EMC, n=8), with a panel of antibodies including PAX2, cyclin D1, p16, vimentin, and Ki67. Loss of PAX2 staining was identified only in EMC but had relatively poor sensitivity for a malignant diagnosis (3/8 cases). Seven EMCs showed p16 expression and staining was diffuse (≥50% cells) in 6 cases, whereas all conventional MGH lesions were negative. However, 1 case of atypical MGH was also p16-positive. Cyclin D1, vimentin, and Ki67 did not reliably distinguish the benign and malignant microglandular lesions because of considerable overlap in staining patterns. In summary, none of the antibodies examined proved completely sensitive and specific, but a p16-positive/PAX2-negative phenotype favored a diagnosis of EMC. Pathologists should be aware that EMC, like some other types of endometrial carcinoma, are commonly p16-positive to avoid misinterpretation as a primary endocervical neoplasm. In practice, correlation of the histologic, immunohistologic, and clinical findings is necessary for accurate interpretation of microgandular-pattern lesions, particularly in small biopsy samples.