Two versus four immunostains for Lynch syndrome screening in endometrial carcinoma

Screening and testing practices for Lynch syndrome in Nova Scotians with endometrial cancer: a descriptive study

BACKGROUND

Identifying people with Lynch syndrome, a genetic condition predisposing those affected to colorectal, endometrial and other cancers, allows for implementation of risk-reducing strategies for patients and their families. The goal of this study was to describe screening and testing practices for this condition among people with endometrial cancer in Nova Scotia, Canada, and to determine the prevalence of Lynch syndrome in this population.

METHODS

All patients diagnosed with endometrial cancer in Nova Scotia between May 1, 2017, and Apr. 30, 2020 were identified through a provincial gynecologic oncology database. Patients from out of province were excluded. We collected age, body mass index, tumour mismatch repair protein immunohistochemistry results, personal and family histories, and germline testing information for all patients.

RESULTS

We identified 465 people diagosed with endometrial cancer during the study period. Most were aged 51 years or older, and had obesity and low-grade early-stage endometrioid tumours. Tumour immunohistochemistry testing was performed in 444 cases (95.5%). Based on local criteria, 189 patients were eligible for genetic counselling, of whom 156 (82.5%) were referred to medical genetics. Of the 98 patients who underwent germline testing, 9 (9.2%) were diagnosed with Lynch syndrome.

INTERPRETATION

The prevalence of Lynch syndrome was at least 1.9% (9/465) in this population. Our results illustrate successful implementation of universal tumour testing; however, there remains a gap in access to genetic counselling.

Validity of a two-antibody testing algorithm for mismatch repair deficiency testing in cancer; a systematic literature review and meta-analysis

Reflex mismatch repair immunohistochemistry (MMR IHC) testing for MLH1, PMS2, MSH2 and MSH6 is used to screen for Lynch syndrome. Recently MMR-deficiency (MMRd) has been approved as a pan-cancer predictive biomarker for checkpoint inhibitor therapy, leading to a vast increase in the use of MMR IHC in clinical practice. We explored whether immunohistochemical staining with PMS2 and MSH6 can be used as a reliable substitute. This two-antibody testing algorithm has the benefit of saving tissue, cutting costs and saving time. PubMed, Embase and Cochrane library were systematically searched for articles reporting on MMR IHC. The weighed percentage of cases with isolated MLH1 or MSH2 loss or combined MLH1/MSH2 loss alone was analyzed using a random effects model meta-analysis in R. The search yielded 1704 unique citations, of which 131 studies were included, describing 9014 patients. A weighed percentage of 1.1% (95% CI 0.53-18.87, I = 87%) of cases with isolated MLH1 or MSH2 loss or combined MLH1/MSH2 loss alone was observed. In the six articles with the main aim of investigating the two-antibody testing algorithm all MMRd cases were detected with the two-antibody testing algorithm, there were no cases with isolated MLH1 or MSH2 loss or combined MLH1/MSH2 loss alone. This high detection rate of MMRd of the two-antibody testing algorithm supports its use in clinical practice by specialized pathologists. Staining of all four antibodies should remain the standard in cases with equivocal results of the two-antibody testing algorithm. Finally, educational sessions in which staining pattern pitfalls are discussed will continue to be important.

MSI testing : What's new? What should be considered?

Based on new trial data regarding immune checkpoint inhibitors (ICIs), the detection of high-grade microsatellite instability (MSI-H) or underlying deficient mismatch repair protein (dMMR) is now becoming increasingly important for predicting treatment response. For the first time, a PD‑1 ICI (pembrolizumab) has been approved by the European Medicines Agency (EMA) for first-line treatment of advanced (stage IV) dMMR/MSI‑H colorectal cancer (CRC). Further indications, such as dMMR/MSI‑H endometrial carcinoma (EC), have already succeeded (Dostarlimab, 2nd line treatment) and others are expected to follow before the end of 2021. The question of optimal testing in routine diagnostics should therefore be re-evaluated. Based on a consideration of the strengths and weaknesses of the widely available methods (immunohistochemistry and PCR), a test algorithm is proposed that allows quality assured, reliable, and cost-effective dMMR/MSI‑H testing. For CRC and EC, testing is therefore already possible at the primary diagnosis stage, in line with international recommendations (NICE, NCCN). The clinician is therefore enabled from the outset to consider not only the predictive but also the prognostic and predispositional implications of such a test when counseling patients and formulating treatment recommendations. As a basis for quality assurance, participation in interlaboratory comparisons and continuous documentation of results (e.g., QuIP Monitor) are strongly recommended.

[Endometrial carcinomas in 2021: What to say and what to do?]

The treatment of endometrial carcinomas relies on histopathological data such as tumor type, grade, stage, and lymphovascular invasion. We herein present the recent advances in the pathological appreciation of these criteria, relying in the last 2020 WHO classification of female genital tumours. Furthermore, molecular typing of endometrial carcinoma has become a rule with strong prognostic and therapeutic implications. The TP53-mutated/serous-like and hypermutated/dMMR groups can be easily identified by the pathologist using immunohistochemistry. The ultramutated/POLE-mutated group identification requires sequencing technologies. We herein explain how easily incorporate this novel histomolecular classification, now included in scholarly society recommendations, in the pathologist routine.

Interlaboratory Concordance of ProMisE Molecular Classification of Endometrial Carcinoma Based on Endometrial Biopsy Specimens

Molecular classifiers improve the consistency of categorization of endometrial carcinoma and provide valuable prognostic information. We aimed to evaluate the interlaboratory agreement in ProMisE assignment across 3 dedicated Canadian gynecologic oncology centers. Fifty cases of endometrial carcinoma diagnosed on biopsy were collected from 3 centers and 3 unstained sections were provided to each participating site so that immunohistochemistry for MSH6, PMS2, and p53 could be performed and interpreted at each center, blinded to the original diagnoses and the results from other centers. A core was taken for DNA extraction and POLE mutation testing. Overall accuracy and κ statistic were assessed. MSH6, PMS2, and p53 could be assessed for all 50 cases, with agreement for 140/150 results. There was a high level of agreement in molecular classification (κ=0.82), overall. Cases with a discordant result for one of the features used in classification (n=10) were reviewed independently and the most common reason for disagreement was attributable to the weak p53 staining in 1 laboratory (n=4). Interpretive error in PMS2 (n=1) and MSH6 (n=2) assessment accounted for 3 of the remaining disagreements. Interpretive error in the assessment of p53 was identified in 2 cases, with very faint p53 nuclear reactivity being misinterpreted as wild-type staining. These results show strong interlaboratory agreement and the potential for greater agreement if technical and interpretive factors are addressed. Several solutions could improve concordance: central quality control to ensure technical consistency in immunohistochemical staining, education to decrease interpretation errors, and the use of secondary molecular testing.

[MSI testing : What is new? What should be considered? German version]

Based on new trial data regarding immune checkpoint inhibitors (ICIs), the detection of high-grade microsatellite instability (MSI-H) or underlying deficient mismatch repair protein (dMMR) is now becoming increasingly important for predicting treatment response. For the first time, a PD‑1 ICI (pembrolizumab) has been approved by the European Medicines Agency (EMA) for first-line treatment of advanced (stage IV) dMMR/MSI‑H colorectal cancer (CRC). Further indications, such as dMMR/MSI‑H endometrial carcinoma (EC), have already succeeded (Dostarlimab, 2nd line treatment) and others are expected to follow before the end of 2021. The question of optimal testing in routine diagnostics should therefore be re-evaluated. Based on a consideration of the strengths and weaknesses of the widely available methods (immunohistochemistry and PCR), a test algorithm is proposed that allows quality assured, reliable, and cost-effective dMMR/MSI‑H testing. For CRC and EC, testing is therefore already possible at the primary diagnosis stage, in line with international recommendations (NICE, NCCN). The clinician is therefore enabled from the outset to consider not only the predictive but also the prognostic and predispositional implications of such a test when counseling patients and formulating treatment recommendations. As a basis for quality assurance, participation in interlaboratory comparisons and continuous documentation of results (e.g., QuIP Monitor) are strongly recommended.

POLE, MMR, and MSI Testing in Endometrial Cancer: Proceedings of the ISGyP Companion Society Session at the USCAP 2020 Annual Meeting

Subclassification of endometrial carcinoma (EC) based on morphologic features alone has been shown to have suboptimal reproducibility, both in regard to biopsy versus hysterectomy findings, as well as interobserver agreement. This restricts the role of morphologic classification of EC as a tool for risk prediction and therefore treatment planning. A diagnostic algorithm based on The Cancer Genome Atlas (TCGA) classification of EC holds promise for improving accuracy in risk prediction. This classifies EC into 4 groups: those harbouring mutations in the exonuclease domain of DNA polymerase epsilon, POLE (POLEmut), those showing a mismatch repair defect, those showing mutations in TP53 (p53abn) and a heterogenous group showing none of these 3 abnormalities (currently termed no specific molecular profile). These groups can be accurately and reproducibly diagnosed on biopsy samples using a limited panel of tests, namely immunohistochemistry for mismatch repair proteins and p53, and testing for POLE exonuclease domain pathogenic variants. In this article we briefly review the biology, testing and interpretation of POLE and mismatch repair defects in EC.

Mismatch repair protein loss in breast cancer: clinicopathological associations in a large British Columbia cohort

Purpose

Alterations to mismatch repair (MMR) pathways are a known cause of cancer, particularly colorectal and endometrial carcinomas. Recently, checkpoint inhibitors have been approved for use in MMR-deficient cancers of any type (Prasad et al. in JAMA Oncol 4:157–158, 2018). Functional studies in breast cancer have shown associations between MMR loss, resistance to aromatase inhibitors and sensitivity to palbociclib (Haricharan et al. in Cancer Discov 7:1168–1183, 2017). Herein, we investigate the clinical meaning of MMR deficiency in breast cancer by immunohistochemical assessment of MSH2, MSH6, MLH1 and PMS2 on a large series of breast cancers linked to detailed biomarker and long-term outcome data.

Methods

Cases were classified as MMR intact when all four markers expressed nuclear reactivity, but MMR-deficient when at least one of the four biomarkers displayed loss of nuclear staining in the presence of positive internal stromal controls on the tissue microarray core.

Results

Among the 1635 cases with interpretable staining, we identified 31 (1.9%) as MMR-deficient. In our cohort, MMR deficiency was present across all major breast cancer subtypes, and was associated with high-grade, low-progesterone receptor expression and high tumor-infiltrating lymphocyte counts. MMR deficiency is significantly associated with inferior overall (HR 2.29, 95% CI 1.02–5.17, p = 0.040) and disease-specific survival (HR 2.71, 95% CI 1.00–7.35, p = 0.042) in the 431 estrogen receptor-positive patients who were uniformly treated with tamoxifen as their sole adjuvant systemic therapy.

Conclusion

Overall, this study supports the concept that breast cancer patients with MMR deficiency as assessed by immunohistochemistry may be good candidates for alternative treatment approaches such as immune checkpoint or CDK4 inhibitors.

Electronic supplementary material

The online version of this article (10.1007/s10549-019-05438-y) contains supplementary material, which is available to authorized users.

Granular dot-like staining with MLH1 immunohistochemistry is a clone-dependent artefact

Immunohistochemistry (IHC) for DNA mismatch repair proteins MLH1, PMS2, MSH2, and MSH6 is used for microsatellite instability (MSI) screening in colorectal carcinoma (CRC) and endometrial carcinoma (EC). Loss of PMS2, with retained MLH1 staining occurs in germline mutations of PMS2 gene, and is an indication for genetic testing. We report a pitfall of immunohistochemical interpretation in an EC, initially regarded as MLH1-positive and PMS2-negative. Review of the MLH1-IHC (M1-clone) revealed a granular, dot-like, nuclear staining. On repeating the MLH1-IHC with a different clone (ES05-clone), complete negativity was noted, and on molecular testing, MLH1 promotor methylation was detected. The dot-like pattern was therefore adjudged a clone-dependent artefact. On reviewing the archived MLH1-IHC slides, we observed the same dot-like pattern in two CRCs; in both cases the M1-clone had been used. Awareness of this artefact may prevent reporting errors, and unnecessary referrals for germline mutation testing.