Adenoid basal hyperplasia of the uterine cervix: a lesion of reserve cell type, distinct from adenoid basal carcinoma.

Adenoid basal hyperplasia is an underrecognized cervical lesion, resembling adenoid basal carcinoma, except the absence of deep invasion into the stroma. We report a series of 10 cases, all extending less than 1 mm from the basement membrane. Our results support the hypothesis that adenoid basal hyperplasia arises from reserve cells of the cervix. Lesions were found close to the squamocolumnar junction, in continuity with the nearby subcolumnar reserve cells. They shared the same morphology and immunoprofile using a panel of 4 antibodies (keratin 5/6, keratin 14, keratin 7 and p63) designed to differentiate reserve cells from mature squamous cells and endocervical columnar cells. We detected no human papillomavirus infection by in situ hybridization targeting high-risk human papillomavirus, which was concordant with the absence of immunohistochemical p16 expression. We demonstrated human papillomavirus infection in 4 (80%) of 5 adenoid basal carcinoma, which is in the same range as previous studies (88%). Thus, adenoid basal hyperplasia should be distinguished from adenoid basal carcinoma because they imply different risk of human papillomavirus infection and of subsequent association with high-grade invasive carcinoma. In our series, the most reliable morphological parameters to differentiate adenoid basal hyperplasia from adenoid basal carcinoma were the depth of the lesion and the size of the lesion nests. Furthermore, squamous differentiation was rare in adenoid basal hyperplasia and constant in adenoid basal carcinoma. Finally, any mitotic activity and/or an increase of Ki67 labeling index should raise the hypothesis of adenoid basal carcinoma.