CME
Physicians: Maximum of 1.00 AMA PRA Category 1 Credit™
ABIM MOC: maximum of 1.00 Medical Knowledge MOC point
Released: November 02, 2023
Expiration: November 01, 2024
Overview of Endometrial Cancer
Endometrial cancer is the most common gynecologic malignancy in the United States and other developed nations, with more than 65,000 women being diagnosed annually.1 The average age at diagnosis is 63 years, and the incidence of endometrial cancer has been increasing by 1% per year since the mid-2000s among women 50 years of age and older.1,2
Most patients are diagnosed with early-stage disease, and the 5-year overall survival (OS) rate for International Federation of Gynecology and Obstetrics (FIGO) stage I-II disease is 74.6% to 86.3%.3 Unfortunately, this rate drops to 28.2% to 48.7% for those diagnosed with stage III-IV disease. We also see racial inequities in OS, with Black women having a 2-fold higher likelihood of dying from endometrial cancer compared with White women.1
The principal risk factor for developing endometrial cancer is obesity.2 Other risk factors include Lynch syndrome—a hereditary condition that we will discuss later in this module—along with type 2 diabetes, history of polycystic ovarian syndrome, use of postmenopausal estrogen, late-onset menopause, and prior tamoxifen use for breast cancer.
Numerous genetic and molecular factors influence outcomes among patients with endometrial cancer. This module focuses on current recommendations for biomarker testing and interpretation in advanced endometrial cancer. We will discuss the specifics for testing after reviewing the clinical importance of key biomarkers and The Cancer Genome Atlas (TCGA) molecular profiles.
Clinical Implications of Key Biomarkers
Shown here is a summary of established and key investigational biomarkers with prognostic and/or predictive roles in the setting of advanced endometrial disease.
The first 3 biomarkers—dMMR, MSI-H, and tumor mutational burden (TMB) high—are well established as predictive of response to immunotherapy.4-6 An important development in 2023 was the adoption of carboplatin/paclitaxel plus either dostarlimab or pembrolizumab as standard of care for the treatment of frontline advanced or recurrent endometrial cancer. Phase III data demonstrated that patients with dMMR/MSI-H endometrial cancer gained significant PFS benefit from these immunotherapy-based regimens.7,8 To learn more about the biologic rationale for using immunotherapy in endometrial cancer with these molecular characteristics, please see this module from my colleague, Lauren Prescott, MD, MPH.
One example of an important emerging predictive biomarker is p53. Data from the phase III SIENDO trial suggest that patients with wild-type TP53 may benefit from selinexor treatment.9,10
As mentioned earlier, HER2 expression and/or gene amplification serves as a predictive biomarker for HER2-directed treatment.4,6 Trastuzumab is the current standard of care, with promising data emerging for trastuzumab deruxtecan in endometrial cancer.11 Trastuzumab deruxtecan was recently added to National Comprehensive Cancer Network (NCCN) guidelines as an option for second- and later-line treatment of endometrial cancer that is HER2 positive (immunohistochemistry [IHC] 3+ or 2+).6
Estrogen receptor (ER)/progesterone receptor (PgR) positivity may be predictive for benefit from hormonal treatment.
Although quite rare in endometrial cancer, NTRK gene fusion is an established predictive biomarker for response to a TRK inhibitor, such as larotrectinib or entrectinib.6
The bottom half of this table lists multiple biomarkers that are still under investigation.4
TCGA Molecular Classification and Outcomes
In addition to the roles described above, the p53 and POLE biomarkers are a critical part of clinically significant molecular profiles in endometrial cancer. In 2013, TCGA identified 4 molecular subgroups based on shared genomic features that correlate with clinical outcomes.12,14
I mentioned earlier that Black women have worse survival outcomes compared with White women diagnosed with endometrial cancer. Unfortunately, molecular features conferring poor prognosis are more common among Black women with endometrial cancer.15 These include more aggressive nonendometrioid histology, higher rates of p53 overexpression—which reflects oncogenic gain-of-function missense mutations in TP53—and HER2 overexpression.
In addition to these molecular features, numerous socioeconomic factors are behind this inequity. My colleague, Ebony Hoskins, MD, discusses strategies that healthcare professionals can use to help improve outcomes in our Black patients with endometrial cancer in this module.
Molecular Subtyping of Endometrial Cancer: PORTEC-3 Trial
Although our focus is predominantly on advanced disease, I do want to mention that the molecular profiles identified by TCGA are predictive of benefit from adjuvant treatment. Shown here is a 2020 analysis of available tissue from the phase III PORTEC-3 trial, which reported that only the copy number–high profile significantly benefited from escalating treatment by combining adjuvant chemotherapy and radiation vs radiation therapy alone.16 Those with dMMR—which causes MSI—or copy number–low profiles did not significantly benefit from adjuvant therapy escalation. Furthermore, the POLE-ultramutated profile had an excellent outcome regardless of therapy, suggesting that patients with this profile may do well with therapy de-escalation.
Molecular Profile and Potential Drugs by TCGA Classification
The TCGA molecular profiles exhibit distinct patterns of PD-L1 expression and mutations in other genes.12,13,17-20 By understanding these patterns, we can better tailor treatment options to individual patients. For example, in the copy number–high group, 25% of patients exhibit HER2 overexpression and/or gene amplification, providing an opportunity for HER2-targeted treatment.
NCCN Guidelines on Molecular Testing in Endometrial Cancer
Now that we have reviewed the clinical roles of key biomarkers, we should discuss how to perform molecular testing.
NCCN guidelines recommend that all patients with endometrial cancer be tested for MMR proteins.6 The guidelines strongly encourage using IHC testing for MMR proteins or testing for MSI—a consequence of dMMR. Their other recommendations are more limited. HER2 testing is recommended for all patients with serous or carcinosarcoma disease. ER/PgR testing is recommended for those with stage III/IV or recurrent disease.
Although not as strong as their universal recommendation for MMR protein testing, NCCN guidelines strongly encourage assessing for hotspot mutations in the exonuclease domain of POLE, performing IHC for p53, and performing comprehensive molecular profiling at the initial assessment. At the end of this module, I will share my institution’s experience with implementing a universal program of comprehensive molecular profiling for all patients newly diagnosed with endometrial cancer.
The guidelines also recommend considering testing for NTRK gene fusions among those with metastatic or recurrent endometrial cancer, as well as testing for TMB status.
Molecular testing can be performed on the initial biopsy, dilation and curettage material, or a final hysterectomy specimen.
SGO and NCCN Recommend Universal Testing for MMR Proteins in Patients With Endometrial Cancer
We will now discuss the specifics of testing for these biomarkers. To start, both the Society of Gynecologic Oncology and the NCCN recommend universal testing for MMR proteins in patients with endometrial cancer.4,6 Testing can be done by IHC for loss of the 4 MMR proteins: MLH1, MSH2, MSH6, and PMS2. In dMMR tumors, the most common patterns are loss of either the MLH1/PMS2 or MSH2/MSH6 heterodimer.21 Most instances of dMMR in endometrial cancer are due to acquired hypermethylation of the promoter for MLH1, with the remainder typically due to germline pathogenic variants or double somatic mutations in MMR genes.22
If MLH1 protein loss is observed, then reflex testing for MLH1 promoter methylation should be performed.4,6 This helps differentiate between somatic loss due to promoter methylation vs potential germline loss.
If these testing results are equivocal, it is recommended to perform testing for MSI, the genomic consequence of dMMR. MSI status can be assessed using either next-generation sequencing (NGS) or multiplex polymerase chain reaction to compare the fragment length of 5 specific microsatellite regions in tumor DNA vs normal DNA. Tumors demonstrating instability in ≥2 of these markers are considered MSI-H.
When to Pursue Germline Testing for Lynch Syndrome
I briefly mentioned that germline pathogenic variants can cause dMMR. Approximately 3% of patients with endometrial cancer have dMMR attributable to Lynch syndrome, a hereditary condition that increases the risk of various cancers through germline variants in the 4 MMR genes (MLH1, MSH2, MSH6, or PMS2).23 Within the subpopulation who have dMMR endometrial cancer, approximately 1 in 10 have Lynch syndrome. Diagnosis of Lynch syndrome is important because it allows for cancer surveillance and cascade testing in relatives of the patient.4,6,24
When should we pursue germline testing for Lynch syndrome? The screening algorithm shown here was developed by the Manchester International Consensus Group in 2019. Based on results of the IHC for MMR proteins and/or MSI testing, the patient should be referred for genetic counseling and germline testing for mutations associated with Lynch syndrome in these scenarios:
Tumor Mutational Burden Testing
Moving on to TMB, this is an important biomarker predictive of response to immunotherapy.4,21,25,26 Currently, TMB can be assessed only as part of a large NGS panel, which comes with the usual limitations regarding slower turnaround and greater cost. That being said, NGS can provide much more information beyond just this biomarker, as we have discussed.
HER2/neu Testing in Serous Endometrial Cancer
HER2-directed therapy is an effective targeted treatment approach for patients with advanced or recurrent HER2-positive endometrial cancer. Among patients with serous endometrial cancer, approximately 25% have HER2 overexpression and/or gene amplification.27,28
Trastuzumab is now part of standard of care for patients with advanced or recurrent HER2-positive serous or carcinosarcoma endometrial cancer.6 This is based on data from a multicenter randomized phase II clinical trial, which demonstrated significantly prolonged PFS and OS with carboplatin and paclitaxel plus trastuzumab vs carboplatin and paclitaxel alone in this setting.28 NCCN guidelines also include trastuzumab deruxtecan as an option for second- and later-line treatment of advanced endometrial cancer that is HER2 positive with an IHC score of 3+ or 2+.6
HER2 testing generally follows the approach used in the phase II trial described above, which was adapted from the criteria used for breast cancer.27,28 Endometrial cancers are considered HER2 positive with an IHC score of 3+, where >30% of the cancer cells exhibit intense complete or lateral/basolateral membranous HER2 immunostaining. The cancer is also considered HER2 positive if it is assigned an equivocal IHC score of 2+ and has fluorescence in situ hybridization (FISH) testing that demonstrates a HER2/CEP17 ratio ≥2.0. An IHC score of 2+ is assigned when ≤30% of the cancer cells exhibit the intense staining described above or when ≥10% exhibit weak to moderate immunostaining.
Despite HER2-directed therapy being standard of care for HER2-positive disease, we still have challenges with HER2 testing.27,28 In contrast to breast cancer, 2 pathology studies have observed that >50% of HER2-positive serous endometrial cancers exhibit very different degrees of HER2 protein expression between tumors in the same patient, correlating with heterogeneous patterns of HER2 gene amplification.29,30
ER/PgR Testing
Turning now to ER/PgR testing, there are no consensus guidelines for reporting the results of ER/PgR IHC testing in endometrial cancer.4 The College of American Pathologists (CAP) recommends using the same approach in reporting as is done with ER/PgR IHC testing in breast cancer.31 Specifically, CAP recommends reporting the proportion of cells with positive staining along with the intensity of nuclear immunostaining. The result is considered positive for ER/PgR if ≥1% of tumor cells exhibit nuclear immunoreactivity, as you can see in these micrographs.
NTRK Gene Fusion Testing
Our final biomarker is NTRK. Tropomyosin kinase receptors (TRKA/B/C) are involved in neural development and encoded by NTRK1/2/3.32,33 NTRK gene fusions can constitutively activate these TRK proteins and their growth pathways, thereby acting as oncogenic drivers in solid cancers.
NTRK gene fusions are quite rare, occurring in only 0.19% of patients with endometrial cancer. In my practice, I have cared for only a couple patients with gynecologic cancers harboring these fusions. Despite their rarity, it is important to discuss testing for NTRK gene fusions, because patients with NTRK fusion–positive tumors benefit from targeted treatment with a TRK inhibitor. In an integrated analysis of clinical trials of entrectinib, the objective response rate was 61% and the median OS was 34 months in patients with NTRK fusion–positive advanced solid tumors.34
NCCN guidelines recommend considering NTRK gene fusion testing in the setting of recurrent or metastatic endometrial cancer. Multiple testing approaches are possible, including IHC, FISH, and DNA or RNA NGS.35 RNA NGS is recommended because it is very sensitive and can directly identify the fusion partner in the transcribed product. Current DNA NGS testing is suboptimal because fusion breakpoints often occur within NTRK introns, which can be very large and highly repetitive—thereby limiting the sensitivity of DNA NGS testing.
Implementing Universal Screening of All Patients Newly Diagnosed With Endometrial Cancer
Now that we have discussed current recommendations for molecular testing in endometrial cancer, I would like to share my institution’s experience in establishing universal comprehensive molecular profiling for every patient newly diagnosed with endometrial cancer, regardless of stage. The H. Lee Moffitt Cancer Center and Research Institute now uses in-house NGS to obtain the molecular profile as the molecular data are included as part of the 2023 FIGO staging report.
When we were developing this initiative, we had a thorough discussion about the patient population whom we should target for molecular profiling. We ultimately decided to go with universal screening, because although tailoring treatment based on molecular characteristics is very important to optimize care of advanced disease, these molecular characteristics also can inform when to de-escalate adjuvant treatment in early-stage disease.
For example, NGS is helpful in a “multicarrier” scenario where p53 testing identifies a TP53 mutation, but NGS reveals POLE ultramutation. Data indicate that the POLE ultramutation usually is the driver, not the TP53 mutation.36,37 As we discussed earlier, patients with POLE-ultramutated disease have an excellent prognosis and are good candidates for adjuvant therapy de-escalation. Thus, comprehensive molecular profiling of a patient with early-stage disease who is a multicarrier would enable healthcare professionals to avoid overtreatment and its risks.
As a second example, a 2023 analysis of the PORTEC-1 and PORTEC-2 studies reported molecular characteristics predictive of benefit from external beam radiation vs vaginal brachytherapy for early-stage endometrial cancer.38 These characteristics are readily obtained with NGS.
As a third example, there is debate around whether patients with stage IB grade 3 disease benefit from chemotherapy.39,40 Molecular profiling can help characterize the aggressiveness of the patient’s disease and inform whether to pursue chemotherapy.
We do face some ongoing technical and logistical challenges in our universal screening initiative. There can be discordance between the NGS results and other molecular tests. For example, the concordance rate between NGS and p53 IHC is more than 90%, but it is not 100%.41 We have encountered situations where the p53 IHC indicates TP53 wild-type but NGS testing indicates TP53 mutation. Similar discrepancies can occur when determining HER2 status and dMMR status by IHC vs MSI testing.
We also must consider insurance and financial issues. In my practice, we are fortunate to have extensive support (eg, grants) to cover some of the costs if the insurance company does not agree with the physician’s decision. Fortunately, since we implemented universal screening at the end of June 2023, I have not had any insurance company deny coverage for our testing.
An outstanding question is whether patients who undergo NGS at diagnosis of early-stage disease should then repeat the NGS at disease recurrence. We need to see more data on the stability of the molecular profile, particularly for somatic mutations. For example, we know that somatic reversion mutations can happen in patients with germline BRCA-mutated disease treated with PARP inhibition.42
Another area for improvement is the development and adoption of NGS assays that can use cell-free circulating tumor DNA. This would allow our patients to avoid undergoing multiple invasive biopsies.
Key Takeaways
Here are the key takeaways from our discussion on molecular testing in endometrial cancer.
First, test all patients with endometrial cancer for MMR proteins by IHC—this has important implications for deciding whether to use an immunotherapy-based regimen.
Second, test patients with serous, carcinosarcoma, or any p53-abnormal disease for HER2 expression by IHC to determine whether they may benefit from anti–HER2-based treatment.
Third, test the patients with advanced or recurrent disease for ER/PgR expression by IHC. Hormonal therapy is an option for those with ER/PgR-positive disease.
Finally, it is ideal to perform a comprehensive molecular profile with NGS at the initial assessment. NGS can help identify actionable biomarkers that are established or under investigation in a clinical trial. To learn more about promising investigational therapies and ongoing clinical trials in endometrial cancer, please see my other module.
Assessment
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