Loss of PTEN function may be scored by mutation or deletions of the DNA coding for the PTEN gene on chromosome 10q23 (Table I), or by non-physiologic absence of the PTEN protein (Tables 2,3). PTEN mutation rates in endometrial tissues are highly dependent on the case selection process, greatest in endometrioid (Type I) cancers compared to non-endometrioid (Type 2, papillary serous, clear cell) cancers (5). Be sure to see the table of PTEN inactivation frequency by histopathologic diagnosis. High prevalence PTEN mutation in otherwise "normal" endometrium suggests that progression efficiency is a major modifier of cancer risk for those women with early premalignant disease.
Greatest PTEN mutational rates of all, 83%(4), are seen in endometrioid adenocarcinomas which are preceded by a premalignant lesion (Table I). This is strong evidence for association of PTEN loss of function with a multi-step progression model in which the premalignant phases(EIN) are already PTEN mutant (1-4).
PTEN null glands are present in Normal, Premalignant, and Malignant Endometrium. Immunohistochemistry has many advantages over DNA sequencing as a method of finding loss of PTEN function. It is technically easier, permitting rapid processing of large series, and allows discovery of rare PTEN protein null glands unaffected by adjacent stroma or PTEN-intact glands. Table 2 shows 43%, 56%, and 63% PTEN null rates, respectively, in 132 endometrial samples diagnosed as (normal) proliferative, unopposed estrogen exposed (Persistent proliferative) and EIN (4). PTEN mutation and/or deletion was confirmed in microdissected PTEN protein null glands of (normal) proliferative endometria, thereby confirming that loss of PTEN protein is caused by changes to the PTEN gene itself. These findings were seen in a variety of clinical settings and specimen types as shown in Table 2. Although the prevalence of PTEN-null glands was high amongst all diagnostic classes, there are dramatic changes in the physical morphology of these clones between diagnostic groups.
Figure 1: PTEN Immunohistochemistry in endometrium. PTEN-null glands (black arrowhead) appear pale green against dark brown staining of surrounding stroma in proliferative (left, Cases 339, 366), persistent proliferative (center, Cases 624, 496), and EIN (right, Cases 847, 593) endometria from six different patients. Brown PTEN-positive glands (white arrowhead) are present in proliferative and persistent proliferative examples for comparison. Scale bar is 500Ám.
Figure 2: Sequence confirmed PTEN mutation in proliferative endometrium. Single-plex PCR and denaturing gradient gel electrophoresis of the exon 5 of PTEN gene. DNA from PTEN-null glands (NULL) have aberrantly migrating species (arrowheads) compared to PTEN expressing (POS) glands. Bidirectional (for, forward; rev, reverse) direct sequence confirmation of mutations is shown in panels below. PTEN immunohistochemistry of these two proliferative endometria is shown in Figure 1, left.
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