Endometrial Carcinoma: Pathology and Genetics
Moderator: Dr. Michael A. Wells
Section 5 -
Molecular Alterations in Non-Endometrioid Carcinomas of the Endometrium
C. Blake Gilks
Vancouver General Hospital and University of British Columbia
Vancouver BC, Canada
The Simple Version
There are two distinct pathways of endometrial carcinogenesis, leading to clinically and
pathologically distinct subtypes of endometrial carcinoma. The first pathway (Type-1 cancers) is
associated with hyperestrogenic states, leading to the development of atypical endometrial hyperplasia,
which progresses to endometrioid carcinoma. The second pathway occurs independent of the growth
promoting effects of estrogen, with the earliest recognisable pathological alteration being endometrial
intra-epithelial carcinoma, which progresses to uterine serous carcinoma. The following table highlights
the important differences between type-1 and type-2 cancers.
TABLE 1. Endometrioid (Type-1) versus Non-Endometrioid (Type-2) Endometrial Carcinomas
The More Complex Version
| ||Endometrioid ||Non-Endometrioid|
|Hyperestrinism/ER expression ||+ ||-|
|Complex atypical hyperplasia ||+ ||-|
|p53 mutation/loss ||- ||+|
|PTEN mutation/loss ||+ ||-|
|Microsatellite instability ||+/- ||-|
While the epidemiological data supports there being two distinct pathways of endometrial
carcinogenesis, the situation in clinical practice is more complex, and much more interesting.
Hendrickson et al. observed that the designations of type-1 and type-2 carcinoma describe "two loose
clinicopathologic clusters or syndromes"  rather than reproducibly recognizable groups. The
designations of type-1 and type-2, indicating tumours arising as a result of estrogenic stimulation, and
independent of estrogen, respectively, have never come into routine use diagnostically; although they can
be readily applied to many cases of endometrial carcinoma, a significant number of cases defy
classification as either type-1 or type-2 carcinoma. Examples of such cases include uterine serous
carcinoma associated with complex atypical hyperplasia, or mixed endometrioid and serous carcinoma.
Therefore, these designations are useful in a general sense in understanding endometrial carcinogenesis
but are an oversimplification and not clinically relevant for anatomical pathologists in routine
day-to-day practice. In contrast, designation of the histological subtype of an endometrial carcinoma is
routinely done in clinical practice and this cell-type assignment is used to guide patient therapy.
Accordingly, in this presentation the focus will be on molecular abnormalities in the clinically
important group of non-endometrioid carcinomas, rather than a discussion of general pathways of
endometrial carcinogenesis. Before discussing these molecular abnormalities we will first review
background information of relevance to surgical pathologists.
The reproducibility of histopathological assessment of endometrioid vs non-endometrioid cell type.
Meaningful studies on molecular abnormalities in subtypes of
endometrial carcinoma can only be done if we, as diagnostic pathologists, can accurately diagnose those
subtypes. Unless we can reproducibly recognise uterine serous and clear cell carcinoma, there cannot be
progress in understanding the molecular events of importance during oncogenesis, or rational introduction
of new treatments. We recently examined interobserver reproducibility in assignment of cell-type of
endometrial carcinomas, based on three reviewers examining a single representative slide from fifty
consecutive cases . There was substantial but not perfect interobserver reproducibility in assignment
of cell-type (kappa = 0.70). This would undoubtedly be lower if only high-grade tumours were considered,
as in common, low-grade endometrial adenocarcinomas of endometrioid-type distinction from uterine serous
carcinoma is not an issue. It is only within the smaller subset of higher grade tumours where this
becomes problematic and although this group of tumours has not been examined specifically, it is likely
that the reproducibility in assignment of cell-type in high grade endometrial cancer is suboptimal As
patient management may vary depending on whether we diagnose uterine serous carcinoma or not, efforts to
improve reproducibility are desperately needed. In the meantime, for research purposes it is possible to
focus on very typical, pure examples of uterine serous or clear cell carcinoma for molecular studies, to
minimise the effect of inter-observer variation in diagnosis, but it is important to remember that these
cases may not be representative of all cases of uterine serous or clear cell carcinoma encountered in
practice, especially mixed tumours.
Association of non-endometrioid carcinomas with inherited cancer susceptibility syndromes (HNPCC, BRCA).
Our insight into the molecular events underlying a number of different
carcinomas has been greatly advanced by understanding the genetic basis of inherited susceptibility to
these cancers. For non-endometrioid carcinomas of endometrium there are two relevant cancer
susceptibility syndromes. Familial breast and ovarian cancer, associated with mutations in BRCA1 and
BRCA2, is associated with little or no increase in the likelihood of developing endometrial carcinoma of
either endometrioid or non-endometrioid type. Case reports have documented patients with germ-line
mutations in BRCA genes who have developed uterine serous carcinoma, but, unlike serous carcinoma or
ovary, tube or peritoneum, uterine or cervical serous carcinomas are not a major contributor to cancer
risk in these patients. Although this is perhaps counterintuitive, given the morphological similarities
of serous carcinoma of ovary/peritoneum/fallopian tube vs serous carcinoma of endometrium, there are
other molecular differences (e.g. frequent expression of WT-1 in the former but not the latter, more
frequent Her-2 amplification in the latter than the former) suggesting that there are fundamental
differences between these serous tumours arising at different anatomic sites.
Endometrial carcinoma is a very significant part of the spectrum of disease associated with Hereditary
Non-Polyposis Colon Cancer (HNPCC) syndrome, being the second most common malignancy after colonic
adenocarcinoma. Endometrial carcinomas associated with HNPCC are more frequently higher grade, and
present with higher advanced stage disease, compared to sporadic cases of endometrial cancer. In a
recent study by Carcangiu et al., endometrial carcinomas arising in HNPCC patients were often of
non-endometrioid type (46.3 % of vs. 53.6 % of endometrioid type) . Many of these non-endometrioid
carcinomas were mixed (e.g. 6 of 11 clear cell carcinomas were mixed clear cell and endometrioid
tumours). This indicates that that mismatch repair defects can contribute to development of some
non-endometrioid carcinomas (more about this later).
Specific genetic abnormalities in non-endometrioid carcinomas
- P53: Mutations in P53 are found in most non-endometrioid
carcinomas, and are the most characteristic genetic abnormality in this set of tumours; the precise
percentage of cases with loss of P53 is impossible to state due to differences in case selection and
methods of testing for P53 mutations. For surgical pathologists, p53 immunostaining is an inexpensive
surrogate for P53 mutational testing; p53 immunoreactivity (defined as strong diffuse nuclear
immunoreactivity) is seen in most cases of non-endometrioid carcinoma . It has been suggested that
p53 immunoreactivity can be used diagnostically to support a diagnosis of uterine serous carcinoma but
this requires correlation with morphology as endometrioid carcinomas also can have mutations of p53, and
not all non-endometrioid carcinomas exhibit p53 immunoreactivity. Loss of p53 function leads to genetic
instability, with the result that there is widespread loss of heterozygosity/allelic imbalance in
non-endometrioid carcinomas with mutant p53, and frequent aneuploidy.
- PTEN, microsatellite instability (MSI), k-RAS: Mutations in PTEN
and k-RAS, while common in endometrioid carcinoma, are rarely encountered in non-endometrioid carcinomas.
MSI is more common in endometrioid carcinomas but is also present in occasional cases of non-endometrioid
carcinomas (11% in the study of Catasus et al. ) and, as noted previously, non-endometrioid
carcinomas are encountered with increased frequency in patients with HNPCC.
- Her-2 amplification: Her-2 amplification was identified in 47% of
cases of uterine serous carcinoma by Santin et al. , and Her-2 amplification was associated with a
significantly worse outcome, compared to those patients whose tumours did not show amplification. This
observation is of great potential impact. It may be that gene amplification events are critical in the
genesis of uterine serous carcinoma, an important discovery given how little we know about genetic events
important in the development of these tumours. Interestingly, Slomovitz et al. did not find this high
frequency of Her-2 amplification in their series of cases , however they included mixed tumours, while
the study of Santin et al. included only pure examples of uterine serous carcinoma. It remains to be
seen whether Herceptin therapy will be effective against uterine serous carcinomas with Her-2
amplification; the amplification ratios were relatively low in most cases, and heterogeneity of Her-2
amplification was seen in 4/14 cases.
Use of Panels of Immunomarkers in Classification of Endometrial Carcinoma
TABLE 2. Immunomarkers in Endometrial Carcinoma
|Marker ||% expression ||p-value|
|Total ||Grade 1&2 endometrioid ||Grade 3 endometrioid ||USC & Clear cell|
|p53 ||16% (25/155) ||2.8% (3/107) ||38% (13/34) ||64% (9/14) ||<0.0001|
|ER ||89% (139/156) ||97% (106/109) ||79% (27/34) ||46% (6/13) ||<0.0001|
|Her2Neu ||4.5% (7/155) ||0% (0/107) ||3% (1/34) ||43% (6/14) ||<0.0001|
|E2F-1 ||24% (37/153) ||18% (19/106) ||32% (11/34) ||54% (7/13) ||0.008|
Table 2 shows the immunophenotype of different subsets of endometrial adenocarcinoma stained at our
centre. It is clear that no single immunomarker can serve as a discriminator between endometrioid and
non-endometrioid carcinomas. An obvious next step is to use panels of immunomarkers that each,
individually, show differences in staining between endometrioid and non-endometrioid carcinomas. When
such data is generated, either supervised or unsupervised analytical approaches can be applied to the
data. With supervised approaches the cases are assigned to categories (e.g. endometrioid vs
non-endometrioid) based on morphological examination. This approach assumes that our morphological
assessment is accurate. In unsupervised analysis, no assumptions are made based on the clinical or
pathological features of the cases, and the immunostaining results are considered completely
independently. Darvishan et al. used a supervised approach to data analysis to demonstrate that the
combination of p53, PR and PTEN were the most useful in distinguishing between uterine serous carcinoma
and endometrioid carcinoma . Using unsupervised hierarchical clustering analysis, and a panel of 9
immunomarkers, we were able to demonstrate that three subsets of endometrial cancer are identifiable .
There is a large group composed of predominantly low grade endometrioid adenocarcinomas that are
characterized by ER +ve, p53 –ve immunophenotype. These are classic type-1 tumors. Another smaller
group of tumours, consisting predominantly of uterine serous carcinoma, shows an ER -ve, p53 +ve
immunophenotype. These are classic type-2 tumors. The third group is characterised by positivity for ER
but also positivity for p53 and/or other oncogenes not typically seen in low-grade endometrioid
carcinoma. It is likely that these tumours start off as lower grade, hormonally sensitive tumours, and
through accumulation of new mutations become higher grade. I suspect that these cases are
under-represented in many of the studies of molecular events during endometrial carcinogenesis, as more
"typical" examples of pure endometrioid or non-endometrioid carcinoma are selected for study. This third
group would account for the finding of atypical hyperplasia in association with non-endometrioid
carcinoma, the mixed endometrioid/non-endometrioid carcinomas in general, and more specifically those
arising in patients with HNPCC syndrome, and the differences in frequency of Her-2 amplification in
studies with different case characteristics
It also suggests that the definition of mixed
adenocarcinoma of the endometrium as "a tumour composed of an admixture of a type-1……and a type-2
carcinoma"  should be revised, as mixed tumors are more likely to be type-1 tumors with progression
to higher grade malignancy.
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- Alkushi A, Abdul-Rahman ZH, Lim P, et al. Am J Surg Pathol, 2005;29:295-304 .
- Carcangiu ML, Dorji T, Radice P, et al. Mod Pathol 2006;19S1:173A.
- Alkushi A, Lim P, Coldman A, et al. Int J Gynecol Pathol 2004;23: 129-137.
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- Santin AD, Bellone S, Van Stedum S, et al. Cancer 2005;104:1391-7.
- Slomovitz RM, Broaddus RR, Burke TW, et al. J Clin Oncol 2004;22:3126-32.
- Darvishan F, Hummer AJ, Thaler HT, et al. Am J Surg Pathol 2004;28:1568-78.
- Alkushi A, Lim P, Coldman A, et al. manuscript submitted.
- Silverberg SG, Kurman RJ, Nogales F, et al. Epithelial tumours and related lesions. World Health Organization Classification of Tumours: IARC Press, 2003:221-32.