Joint loss of PAX2 and PTEN expression in endometrial precancers and cancer

Abstract

Latent endometrial carcinoma precancers are normal-appearing endometrial glands with sporadic loss of tumor suppressor gene function such as PTEN. Progression to carcinoma is inefficient and requires additional genetic damage that creates a histologic precursor lesion called endometrial intraepithelial neoplasia (EIN). In this study, we examined loss of PAX2 expression, a gene required for embryonic uterine development, during endometrial carcinogenesis. Normal proliferative, EIN, and malignant (endometrial adenocarcinoma) endometrial tissues were immunostained for PTEN and PAX2. Proliferative samples with loss of protein in at least one gland were scored as latent precancers. EIN and cancer lesions were scored by the majority pattern. Overall prevalence and topography of joint PAX2-PTEN expression loss was examined. The prevalence of PAX2 protein loss in the sequence of normal to precancer to cancer was 36%, 71%, and 77%, respectively, and for PTEN, it was 49%, 44%, and 68%, respectively. The normal endometrial prevalence of PAX2- or PTEN-deficient latent precancers was unaffected by biopsy indication, but increased significantly with age. Coincident loss of PAX2 and PTEN expression in an individual normal endometrium was seen in 21% of patients, but usually involved different glands. Coincident loss was more common in precancers (31%) and carcinoma (55%), in which case, both markers were protein null in an overlapping clonal distribution. PAX2 and PTEN protein loss occurs independently and accumulates with increasing age in latent precancers of normal premenopausal endometrium. Loss of function of both genes in an overlapping distribution characterizes the clinical emergence of a premalignant lesion which is carried forward to carcinoma.

Figure 1. Overlapping PAX2 and PTEN protein loss in EIN and adenocarcinoma lesions

Premalignant EIN (top row) and malignant carcinoma (bottom row) lesions are clonal neoplasms offset by background endometrial glands (separated by the dashed line). Routine stains (hematoxylin and eosin, “H&E,” left) of EIN and carcinoma show crowded areas of glands with altered cytology which on immunostaining of adjacent sections with PTEN (center) and PAX2 (right) are seen to be protein deficient. Examples of protein deficient glands are marked with “*”, and examples of protein expressing glands marked with “o”. In expressing tissues, stroma and glands stain for PTEN, whereas PAX2 expression is confined to glandular nuclei. Note overlap of loss of both markers within all glands of the lesion.

Figure 2. Non-Overlapping PTEN (center left circle and left inset) and PAX2 (center right triangle and right inset) protein loss in normal proliferative endometrium of a single patient

PTEN protein null glands are independent of those deficient for PAX2 protein. Adjacent serial sections show the same tissue areas stained with PTEN and PAX2. This case overall would be scored (as in Table 2 and Supplemental Table 1) as containing both PTEN and PAX2 null glands, but the illustrated fragment has no individual glands lacking both PTEN and PAX2 proteins.

Figure 3. Somatically acquired sporadic loss of PAX2 and PTEN protein function is age dependent in normal proliferative endometrial tissues (ANOVA p=0.002)

Notched box plot of patient age at time of endometrial biopsy with the specified PAX2 and PTEN immunostain findings. Each solid circle is one patient, boxes indicate central 50% of values, notches are confidence intervals, and whiskers represent 1.5 times the interquartile range. “wt” = wild type, protein expressed in all glands. “null” = latent precancer with isolated protein deficient glands.