Clone Progression

PTEN Mutant Clone Progression

PTEN mutant cells (pale glands below) appear in the histologically normal endometrium of over 1/3 of premenopausal women, but very few of these make it to carcinoma. This section reviews the Morphologic and Functional evolution of mutant endometrial clones from initiation to formation of carcinoma.

A Morphologic Scenario

"Normal" Proliferative Endometrium: PTEN null glands are a small fraction of all endometrial glands, appearing as isolated tubular glands to small clusters of otherwise undistinguished glands. Cytology, gland density, and gland size, are all identical to PTEN expresssing glands.

Persistent Proliferative Endometrium (anovulatory, unopposed estrogens): PTEN null glands undergo architectural changes exactly in parallel with those seen in PTEN expressing glands exposed to estrogens for a protracted interval. This includes a slightly increased gland density and increased average gland size, without any PTEN-specific alterations in cytology.

EIN, Endometrial Intraepithelial Neoplasia: PTEN null glands are comprised of cells with a cytology clearly distinctive from background PTEN expressing glands ("cytologic demarcation). The architecture also diverges between PTEN-null and expressing glands: sharp increases in density of PTEN-null glands is responsible for the rapid deline in Volume Percentage Stroma that characterizes EIN lesions.

A Functional Scenario

1)Initiation:
Initiation of PTEN-mutant clones is common in endometria of premenopausal women and once acquired is stably maintained by a cell population that is incompletely shed during menses (Table 1). PTEN-null cells are thus represented in the regenerative pool of cells which are the source for regeneration following menses. Although ~40% of premenopausal women acquire mutant PTEN-null glands, only 2.4% of them will ever get endometrial cancer, most following menopause. This suggests that acquiring an initial mutation is not the rate limiting step in endometrial carcinogenesis, but that progression of these clones through expansion and acquisition of additional genetic damage is a strong co-determinant of risk. Hormonal factors are attractive as putative modulators of this process, since mutant clones lose their normal ability to increase PTEN expression in response to estrogens.

2)Persistence:
PTEN null glands in the histologically normal (proliferative) endometrium of cycling premenopausal women persist between menstrual cycles (5) (Table I).
PTEN protein status in repeat biopsies of premenopausal women with endogenously cycling proliferative endometrium. Initial (1st sample) and repeat (2nd sample) endometrial samples scored as PTEN-nonexpressing (null) or having only PTEN-expressing glands (positive).

	2nd Sample PTEN positive	2nd Sample PTEN null	Total
1st Sample PTEN positive	15	7	22
1st Sample PTEN null	2	10	12
Total	17	17	34

3)Progression:
A functional Model of carcinogenesis is based upon the premise that acquired genetic lesions are clonally propagated, and host conditions dynamically define the selective advantage of evolving clones. Image analysis (See Box plot below) of PTEN immunohistochemistry is the basis for the following features which distinguish specific types of endometria.

Normal Proliferative: PTEN-null glands are cytologically and architecturally indistinguishable from PTEN-expressing glands in normal proliferative and anovulatory endometrium.
Persistent Proliferative (anovulatory): PTEN null and normal glands enlarge under the protracted influence of estrogens in the transition from normal to anovulatory endometrium.
EIN: Progression to EIN is accompanied by cytologic demarcation of PTEN null glands, with an increase in PTEN-null gland density (correspondingly, volume percentage stroma decreases).
Carcinoma: Malignant transformation occurs when the neoplastic glands outcompete the stroma. This is seen as one or more of the following: myometrial invasion, large solid areas of neoplastic epithelium, or "rambling" mazelike glands.

Morphometric progression of PTEN-null glands. Box plots of PTEN-null gland morphometric variables measured within a 1 mm round sampling window in slides stained for PTEN protein. Histologic classification as proliferative (n=20, PE), persistent proliferative (n=20,"PPE") or EIN (n=17). In the progression sequence PE > PPE > EIN, PTEN null glands occupy an increasing volume of the tissue sample (VPNULL%). This increase is due to the combined effects of increased density (DENNULL) and size (SZNULL) of PTEN-null glands.