Folate receptor alpha expression in low-grade serous ovarian cancer: Exploring new therapeutic possibilities.

OBJECTIVE: Mirvetuximab soravtansine may be a potentially effective therapeutic option for ovarian low-grade serous carcinoma (LGSC), but the prevalence of folate receptor alpha (FRα) overexpression in this tumor type is unknown. We sought to characterize FRα expression in LGSC and its association with clinical and molecular features. METHODS: FRα immunohistochemistry was performed on a tissue microarray comprised of 89 LGSCs and 42 ovarian serous borderline tumors (SBTs). Clinical tumor-normal panel-based sequencing was performed on 78 LGSCs. Associations between FRα-high status and clinicopathologic characteristics and survival outcomes were examined. RESULTS: Of 89 LGSCs, 36 (40%) were FRα-high (≥75% of viable tumor cells exhibiting moderate-to-strong membranous expression). Of 9 patients with LGSC and samples from different timepoints, 4 (44%) had discordant results, with conversion from FRα-negative to FRα-high in 3 (33%) cases. There was no association between FRα-high status with age, race, or progression-free/overall survival. A MAPK pathway genetic alteration, most commonly involving KRAS (n = 23), was present in 45 (58%) LGSCs. Those lacking MAPK pathway alterations were more likely to be FRα-high compared to MAPK-altered LGSCs (61% vs 20%, p < 0.001). In SBTs, FRα-high expression was associated with high-risk (micropapillary) histology and/or subsequent LGSC recurrence compared to conventional SBTs without malignant recurrence (53% vs 9%, p = 0.008). CONCLUSIONS: Future studies of FRα-directed therapy in patients with LGSC are warranted. Discordant FRα status at recurrence suggests potential benefit for retesting. A biomarker-driven approach to direct treatment selection in LGSC is recommended. As high FRα expression is more common amongst tumors lacking MAPK pathway genetic alterations, FRα testing to determine eligibility for mirvetuximab soravtansine therapy is particularly recommended for this subgroup.

Molecular profiling of primary endometrioid endometrial cancer and matched lung metastases: CTNNB1 mutation as a potential driver.

•Both primary endometrial cancers (ECs) and matched lung metastases shared a common ancestor with independent evolution at each site.•The two endometrioid ECs studied acquired additional mutations during the distant metastatic process.•Subclonal CTNNB1 hotspot mutations in the two primary ECs studied became clonal in the distant metastases.

Morphologic and Molecular Heterogeneity of High-grade Serous Carcinoma Precursor Lesions.

Serous tubal intraepithelial carcinoma (STIC) is the fallopian tube precursor lesion for most cases of pelvic high-grade serous carcinoma (HGSC). To date, the morphologic, molecular, and clinical heterogeneity of STIC and a less atypical putative precursor lesion, termed serous tubal intraepithelial lesion, has not been well characterized. Better understanding of precursor heterogeneity could impact the clinical management of women with incidental STICs (without concurrent carcinoma) identified in cases of prophylactic or opportunistic salpingectomy. This study analyzed morphologic and molecular features of 171 STICs and 21 serous tubal intraepithelial lesions. We assessed their histologic features, Ki-67 and p53 staining patterns, and genome-wide DNA copy number alterations. We classified all precursor lesions into 2 morphologic subtypes, one with a flat surface (Flat) and the other characterized by budding, loosely adherent, or detached (BLAD) morphology. On the basis of pathology review by a panel of 8 gynecologic pathologists, we found 87 BLAD, 96 Flat, and 9 indeterminate lesions. As compared with Flat lesions, BLAD lesions were more frequently diagnostic of STIC ( P <0.0001) and were found concurrently with HGSC ( P <0.0001). BLAD morphology was also characterized by higher Ki-67 proliferation index ( P <0.0001), presence of epithelial stratification ( P <0.0001), and increased lymphocyte density ( P <0.0001). BLAD lesions also exhibited more frequent DNA copy number gain/amplification at the CCNE1 or CMYC loci canonical to HGSCs ( P <0.0001). Both BLAD morphology and STIC diagnoses are independent risk factors for an elevated Ki-67 proliferation index. No correlation was observed between BLAD and Flat lesions with respect to patient age, presence of germline BRCA1/2 mutation, or p53 staining pattern. These findings suggest that tubal precursor lesions are morphologically and molecularly heterogeneous, laying the foundation for further studies on the pathogenesis of HGSC initiation and identifying histologic features predictive of poor patient outcomes.

A phase 2 trial of zanidatamab in HER2-overexpressed advanced endometrial carcinoma and carcinosarcoma (ZW25-IST-2).

OBJECTIVE: HER2 overexpression is associated with decreased overall survival in metastatic endometrial cancer. Trastuzumab with chemotherapy has demonstrated efficacy for first-line management of advanced HER2+ endometrial carcinoma, but HER2-directed therapy in the recurrent setting is limited. Zanidatamab (ZW25), a humanized, bispecific antibody that simultaneously binds the 2 distinct HER2 epitopes bound by trastuzumab and pertuzumab, has demonstrated safety and activity in HER2+ tumors. Here, we report the results of a phase 2, open-label study evaluating the efficacy and safety of zanidatamab in patients with HER2+ metastatic endometrial carcinoma/carcinosarcoma who received prior treatment. METHODS: We enrolled 16 patients with HER2+ endometrial carcinoma/carcinosarcoma after progression on ≤2 lines of therapy on a single-arm phase 2 study of zanidatamab. The primary endpoint was overall response rate (ORR; complete or partial response) by Response Evaluation Criteria in Solid Tumors version 1.1. HER2 immunohistochemistry and fluorescence in situ hybridization (FISH) were performed on pretreatment samples. Intratumor HER2 genetic heterogeneity was assessed. RESULTS: This study did not meet its primary efficacy endpoint. Although a clinical benefit rate of 37.5% was observed by 24 weeks, only 1 patient achieved a partial response (ORR, 6.2%). Eight patients had HER2 intratumor heterogeneity or lacked HER2 amplification by FISH. Decreased HER2 expression on repeat pretreatment samples was observed in 3 (75%) of 4 patients evaluated. CONCLUSIONS: We observed a low response rate to zanidatamab in recurrent HER2+ endometrial carcinoma/carcinosarcoma, which may be driven by downregulation of HER2 expression. Repeat HER2 testing should be considered prior to second-line HER2-directed therapy. CLINICALTRIALS: govidentifier: NCT04513665.

Aneuploidy Landscape in Precursors of Ovarian Cancer.

PURPOSE: Serous tubal intraepithelial carcinoma (STIC) is now recognized as the main precursor of ovarian high-grade serous carcinoma (HGSC). Other potential tubal lesions include p53 signatures and tubal intraepithelial lesions. We aimed to investigate the extent and pattern of aneuploidy in these epithelial lesions and HGSC to define the features that characterize stages of tumor initiation and progression. EXPERIMENTAL DESIGN: We applied RealSeqS to compare genome-wide aneuploidy patterns among the precursors, HGSC (cases, n = 85), and histologically unremarkable fallopian tube epithelium (HU-FTE; control, n = 65). On the basis of a discovery set (n = 67), we developed an aneuploidy-based algorithm, REAL-FAST (Repetitive Element AneupLoidy Sequencing Fallopian Tube Aneuploidy in STIC), to correlate the molecular data with pathology diagnoses. We validated the result in an independent validation set (n = 83) to determine its performance. We correlated the molecularly defined precursor subgroups with proliferative activity and histology. RESULTS: We found that nearly all p53 signatures lost the entire Chr17, offering a "two-hit" mechanism involving both TP53 and BRCA1 in BRCA1 germline mutation carriers. Proliferatively active STICs harbor gains of 19q12 (CCNE1), 19q13.2, 8q24 (MYC), or 8q arm, whereas proliferatively dormant STICs show 22q loss. REAL-FAST classified HU-FTE and STICs into 5 clusters and identified a STIC subgroup harboring unique aneuploidy that is associated with increased proliferation and discohesive growth. On the basis of a validation set, REAL-FAST showed 95.8% sensitivity and 97.1% specificity in detecting STIC/HGSC. CONCLUSIONS: Morphologically similar STICs are molecularly distinct. The REAL-FAST assay identifies a potentially "aggressive" STIC subgroup harboring unique DNA aneuploidy that is associated with increased cellular proliferation and discohesive growth. REAL-FAST offers a highly reproducible adjunct technique to assist the diagnosis of STIC lesions.

Decreased HER2 expression in endometrial cancer following anti-HER2 therapy.

Trastuzumab has demonstrated clinical efficacy in the treatment of HER2-positive serous endometrial cancer (EC), which led to its incorporation into standard-of-care management of this aggressive disease. Acquired resistance remains an important challenge, however, and its underlying mechanisms in EC are unknown. To define the molecular changes that occur in response to anti-HER2 therapy in EC, targeted next-generation sequencing (NGS), HER2 immunohistochemistry (IHC), and fluorescence in situ hybridization (FISH) were performed on pre- and post-treatment tumour samples from 14 patients with EC treated with trastuzumab or trastuzumab emtansine. Recurrent tumours after anti-HER2 therapy acquired additional genetic alterations compared with matched pre-treatment ECs and frequently showed decreased HER2 protein expression by IHC (7/14, 50%). Complete/near-complete absence of HER2 protein expression (score 0/1+) observed post-treatment (4/14, 29%) was associated with retained HER2 gene amplification (n = 3) or copy number neutral status (n = 1). Whole-exome sequencing performed on primary and recurrent tumours from the latter case, which exhibited genetic heterogeneity of HER2 amplification in the primary tumour, revealed selection of an early HER2-non-amplified clone following therapy. Our findings demonstrate that loss of target expression, by selection of HER2-non-amplified clones or, more commonly, by downregulation of expression, may constitute a mechanism of resistance to anti-HER2 therapy in HER2-positive EC. © 2023 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

HER2 Genetic Intratumor Heterogeneity Is Associated With Resistance to Trastuzumab and Trastuzumab Emtansine Therapy in Recurrent High-Grade Endometrial Cancer.

Anti-HER2 targeted therapies have recently demonstrated clinical activity in the treatment of high-grade endometrial carcinomas (ECs), particularly serous carcinomas with HER2 amplification and/or overexpression. Intratumor heterogeneity of HER2 amplification or HER2 genetic intratumor heterogeneity (G-ITH) has been associated with resistance to anti-HER2 therapies in breast and gastroesophageal cancers; however, its clinical relevance in EC is unknown. To characterize HER2 G-ITH in EC, archival specimens from a clinically annotated cohort of 57 ECs treated with trastuzumab or trasutuzmab emtansine in the recurrent (n = 38) or adjuvant (n = 19) setting were subjected to central pathology review, HER2 assessment by immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH), and next-generation sequencing. HER2 G-ITH, defined as HER2 amplification in 5% to 50% of tumor cells examined by FISH, was identified in 36% (19/53) of ECs and was associated with lower HER2 copy number and levels of protein expression. HER2 IHC revealed spatially distinct areas of strong expression juxtaposed with areas of low/absent expression in tumors with the "cluster" pattern of G-ITH, whereas the "mosaic" pattern was typically associated with a diffuse admixture of cells with variable levels of HER2 expression. HER2 G-ITH was frequently observed in cases with IHC/FISH or FISH/next-generation sequencing discrepancies and/or with an equivocal/negative FISH result (9/13, 69%). Although the objective response rate to anti-HER2 therapy in recurrent ECs was 52% (13/25) for tumors lacking HER2 G-ITH, none (0%, 0/10) of the patients with HER2 G-ITH achieved a complete or partial response (P = .005). HER2 G-ITH was significantly associated with worse progression-free survival (hazard ratio, 2.88; 95% CI, 1.33-6.27; P = .005) but not overall survival. HER2 IHC score, HER2/CEP17 ratio, HER2 copy number, histologic subtype, and other genetic alterations, including PIK3CA hotspot mutations, were not significantly associated with therapeutic response or survival outcomes. Treatment responses were not restricted to serous carcinomas, supporting consideration of anti-HER2 therapy in patients with HER2-positive high-grade ECs of non-serous histology. Our results demonstrate that HER2 G-ITH is an important determinant of response to trastuzumab and trastuzumab emtansine in EC, providing a rationale for the development of novel therapeutic strategies to target HER2-nonamplified resistant tumor subpopulations, such as HER2 antibody-drug conjugates with bystander effects.

The highs and lows of serous ovarian cancer.

Low-grade serous ovarian cancer was initially described as a distinct type of rare epithelial ovarian cancer 20 years ago; however, only recently have physicians begun to leverage the understanding of the clinical behavior and molecular profile of this disease for treatment. The use of routine next-generation sequencing has allowed a deeper understanding of the molecular drivers of this disease and shown how molecular alterations in mitogen-activated protein kinase pathway genes such as KRAS and BRAF can affect overall prognosis and disease behavior. The use of targeted therapies, including MEK inhibitors, BRAF kinase inhibitors, and other investigational targeted therapies are changing the way this disease is viewed and treated. In addition, endocrine therapy can provide prolonged disease stability with generally mild toxicity, as well as promising response rates in recent studies examining combination therapy with CDK 4/6 inhibitors in the upfront and recurrent setting. Once seen merely as a chemo-resistant form of ovarian cancer, recent studies have worked to harness the unique features of low-grade serous ovarian cancer to provide individualized treatment options for patients with this disease.

Interobserver Reproducibility in Assessing Eosinophilic Cells in Ovarian Serous Borderline Tumors to Predict BRAF Mutational Status.

Ovarian serous borderline tumors (SBTs) harboring the BRAFV600E mutation are associated with decreased risk of progression to low-grade serous carcinoma, and often prominently feature tumor cells with abundant eosinophilic cytoplasm. Since eosinophilic cells (ECs) may be a marker of the underlying genetic driver, we proposed morphologic criteria and evaluated the interobserver reproducibility for assessing this histologic feature. Following the completion of an online training module, representative tumor slides from 40 SBTs ( BRAFV600E -mutated, n=18, BRAF -wildtype, n=22) were independently reviewed by 5 pathologists. For each case, reviewers provided a semiquantitative assessment of the extent of ECs (0: absent, 1: <10%, 2: 10%-50%, or 3: >50%, of tumor area). Interobserver reproducibility for estimating the extent of ECs was moderate (κ=0.41). Applying a cut-off score of ≥2, the median sensitivity and specificity for predicting BRAFV600E mutation were 67% and 95%, respectively. With a cut-off score of ≥1, median sensitivity and specificity were 100% and 82%, respectively. Morphologic mimics of ECs, including tumor cells with tufting or hobnail change and detached cell clusters in micropapillary SBTs, were possible contributing factors for discordant interobserver interpretations. BRAFV600E immunohistochemistry showed diffuse staining in BRAF -mutated tumors, including those with few ECs. In conclusion, the finding of extensive ECs in SBT is highly specific for BRAFV600E mutation. However, in some BRAF -mutated SBTs, ECs may be focal and/or difficult to distinguish from other tumor cells with overlapping cytologic features. The morphologic finding of definitive ECs, even when scarce, should therefore prompt consideration for BRAFV 600E mutation testing.

Chemotherapy response in low-grade serous ovarian carcinoma at a comprehensive cancer center: Readdressing the roles of platinum and cytotoxic therapies.

BACKGROUND: Data on platinum sensitivity of low-grade serous ovarian carcinoma (LGSOC) in the upfront setting is lacking, and there is limited and contradictory information on chemotherapy responses in recurrent disease. METHODS: Patients with LGSOC seen at a comprehensive cancer center from January 1, 1998 to September 30, 2021 were identified from institutional databases. Response to neoadjuvant chemotherapy (NACT) or adjuvant platinum-based chemotherapy and to second- to fifth-line regimens was retrospectively characterized by Response Evaluation Criteria in Solid Tumors (RECIST) v1.1. Wilcoxon rank-sum and two-tailed Fisher exact tests were employed. RESULTS: Of 50 patients, 12 received platinum doublets for suboptimal residual disease and 11 as NACT. Of 12 patients with suboptimal residual disease, seven (58%) achieved objective responses (five partial responses [PRs] and two complete responses); of the 11 patients who underwent NACT, one (9%) achieved a PR (p = .027). The 15 remaining patients had stable disease on first-line platinum chemotherapy. Of 44 patients who recurred, 20 had RECIST-evaluable responses to second-line and 27 to third-line chemotherapy. Objective response rates to platinum-based chemotherapy were 22% (two of nine) in the second line and 10% (one of 10) in the third. In second and third lines, highest response rates were observed with nonplatinum chemotherapy with bevacizumab, at 100% (two of two) and 30% (three of 10), respectively. CONCLUSIONS: Primary platinum-based chemotherapy has moderate activity in LGSOC and minimal activity in the recurrent setting, suggesting standard definitions of platinum sensitivity may not apply in LGSOC. In the second and third lines, nonplatinum chemotherapy/bevacizumab elicited the highest response rates.

Deep Interactive Learning-based ovarian cancer segmentation of H&E-stained whole slide images to study morphological patterns of BRCA mutation.

Deep learning has been widely used to analyze digitized hematoxylin and eosin (H&E)-stained histopathology whole slide images. Automated cancer segmentation using deep learning can be used to diagnose malignancy and to find novel morphological patterns to predict molecular subtypes. To train pixel-wise cancer segmentation models, manual annotation from pathologists is generally a bottleneck due to its time-consuming nature. In this paper, we propose Deep Interactive Learning with a pretrained segmentation model from a different cancer type to reduce manual annotation time. Instead of annotating all pixels from cancer and non-cancer regions on giga-pixel whole slide images, an iterative process of annotating mislabeled regions from a segmentation model and training/finetuning the model with the additional annotation can reduce the time. Especially, employing a pretrained segmentation model can further reduce the time than starting annotation from scratch. We trained an accurate ovarian cancer segmentation model with a pretrained breast segmentation model by 3.5 hours of manual annotation which achieved intersection-over-union of 0.74, recall of 0.86, and precision of 0.84. With automatically extracted high-grade serous ovarian cancer patches, we attempted to train an additional classification deep learning model to predict BRCA mutation. The segmentation model and code have been released at https://github.com/MSKCC-Computational-Pathology/DMMN-ovary.

Mullerian adenosarcoma: clinicopathologic and molecular characterization highlighting recurrent BAP1 loss and distinctive features of high-grade tumors.

Mullerian adenosarcoma is an uncommon mesenchymal tumor of the gynecologic tract. Most cases are low-grade, while high-grade adenosarcomas are rare and not well studied. Herein, we characterize the clinicopathologic and molecular features of 27 adenosarcomas of gynecologic origin, enriched for high-grade tumors subjected to targeted panel sequencing. Sarcomatous overgrowth was more frequently seen in high-grade compared to low-grade tumors (12/17, 71%, vs 1/10, 10%, p = 0.004) and heterologous elements were exclusive to high-grade cases (n = 7, p = 0.03). All deaths were from high-grade disease (advanced primary, n = 2, or recurrence, n = 5). Genetic alterations specific to high-grade adenosarcomas have known associations with chromosome instability, including TP53 mutations (n = 4) and amplifications of MDM2 (n = 2) and CCNE1 (n = 2). Somatic ATRX frameshift mutations were found in 2 patients with high-grade recurrences following a primary low-grade adenosarcoma and ATRX deletion in 1 high-grade adenosarcoma with an adjacent low-grade component. The fraction of genome altered by copy number alterations was significantly higher in high-grade compared to low-grade adenosarcomas (P = 0.001). Other recurrent genetic alterations across the entire cohort included BAP1 homozygous deletions (n = 4), DICER1 mutations (n = 4), ARID1A mutations (n = 3), TERT promoter mutations (n = 2) and amplification (n = 1), as well as alterations involving members of the PI3K and MAPK signaling pathways. One tumor harbored an ESR1-NCOA3 fusion and another had an MLH1 homozygous deletion. Immunohistochemical analysis for BAP1 revealed loss of nuclear expression in 6/24 (25%) cases, including all four tumors with BAP1 deletions. Notably, out of 196 mesenchymal neoplasms of gynecologic origin, BAP1 homozygous deletion was only found in adenosarcomas (P = 0.0003). This study demonstrates that high-grade adenosarcomas are heterogeneous at the molecular level and are characterized by genomic instability and TP53 mutations; ATRX loss may be involved in high-grade transformation of low-grade adenosarcoma; and BAP1 inactivation appears to be a specific pathogenic driver in a subset of adenosarcomas.

Advancements in Low-Grade Serous Carcinoma of the Ovary and Peritoneum.

PURPOSE OF REVIEW: Low-grade serous ovarian cancer (LGSOC) is a rare form of epithelial ovarian cancer that generally exhibits a protracted course and is less sensitive to chemotherapy than high-grade serous ovarian cancer. Over the past decade, it has become clear that patients with LGSOC have a clinically distinct course and are molecularly and histologically unique from patients with high-grade serous ovarian cancer. RECENT FINDINGS: Endocrine therapy is frequently used for the treatment of patients with recurrent LGSOC and is now also part of the standard upfront treatment of this disease, with an ongoing phase III clinical trial seeking to determine if chemotherapy can be eliminated altogether from the initial treatment of LGSOC. Tumors are frequently found to exhibit alterations affecting the mitogen-activated protein kinase (MAPK) pathway, recently leading to developments in the use of targeted treatments for those patients with recurrent disease. LGSOC is a clinically, histologically, and molecularly unique form of epithelial ovarian cancer. Recent advances in the understanding of endocrine and molecular drivers of this disease have led to changes in both the treatment of newly diagnosed and recurrent disease, with ongoing studies focused on refining upfront therapy and seeking novel targeted combinations for those patients with recurrent disease.

MAPK Pathway Genetic Alterations Are Associated with Prolonged Overall Survival in Low-Grade Serous Ovarian Carcinoma.

PURPOSE: To characterize the somatic mutational landscape, investigate associations between genetic alterations and clinical outcomes, and determine the prevalence of pathogenic germline mutations in low-grade serous ovarian carcinomas (LGSC). EXPERIMENTAL DESIGN: Patients with LGSC tumors who underwent panel-based sequencing of up to 505 genes were identified. Data on somatic and germline mutations; copy-number alterations; and clinicopathologic features, including age at diagnosis, platinum sensitivity, and overall survival (OS), were collected. RESULTS: Following central pathology rereview, 119 patients with LGSC were identified for analysis. Of these, 110 (92%) had advanced-stage disease (stages III/IV). Somatic KRAS (33%), NRAS (11%), EIF1AX (10%), and BRAF (11%) alterations were the most common; MAPK pathway alterations were found in 60% (n = 71) of LGSCs. KRAS mutations were significantly associated with age at diagnosis more than 50 years (P = 0.02) and platinum-sensitive disease (P = 0.03). On multivariate analysis, MAPK pathway alterations (P = 0.02) and platinum sensitivity (P = 0.005) were significantly associated with improved OS. Seventy-nine patients (66%) underwent germline genetic testing; seven pathogenic germline mutations were identified: MUTYH (n = 2), BAP1 (n = 1), RB1 (n = 1), CHEK2 (n = 1), APC (n = 1), and FANCA (n = 1). There were no germline BRCA1/2 mutations. One germline MUTYH-associated LGSC harbored loss-of-heterozygosity at the MUTYH locus, and the patient with the germline BAP1 mutation also harbored a somatic BAP1 frameshift mutation. CONCLUSIONS: This study showed that MAPK pathway alterations in LGSC, including KRAS mutations, are independently associated with platinum sensitivity and prolonged survival. Germline data, which were limited, identified few pathogenic germline mutations in patients with LGSC. See related commentary by Veneziani and Oza, p. 4357.

Pre-clinical activity of the oral DNA-PK inhibitor, peposertib (M3814), combined with radiation in xenograft models of cervical cancer.

DNA-dependent protein kinase (DNA-PK) plays a crucial role in repair of DNA double-strand breaks by facilitating non-homologous end-joining. Inhibitors of DNA-PK have the potential to block DNA repair and enhance DNA-damaging agents. Peposertib (M3814) is a DNA-PK inhibitor that has shown preclinical activity in combination with DNA-damaging agents, including ionizing radiation (IR) and topoisomerase II inhibitors. Here we evaluated the activity of peposertib (M3814) in combination with radiation in a mouse xenograft model of HPV-associated cervical cancer. Athymic nude female mice with established tumors derived from HeLa cells injected into the flank were treated with vehicle alone (n = 3), IR alone (n = 4), and peposertib (M38814) in combination with IR (M3814 + IR; n = 4). While IR alone was associated with a trend towards decreased tumor volume compared with untreated, only the M3814 + IR treatment arm was associated with consistent and significant reduction in tumor burden, which correlated with higher levels of γ-H2AX in tumor cells, a marker of double-strand DNA breaks. Our data support further clinical evaluation of the combination of peposertib (M38814) and IR in cervical cancer.

Histopathologic features and molecular genetic landscape of HER2-amplified endometrial carcinomas.

HER2 is an established therapeutic biomarker in advanced or recurrent endometrial serous carcinoma. Current clinical guidelines recommend HER2 testing exclusively in this endometrial carcinoma (EC) subtype; however, the full spectrum of ECs harboring HER2 amplification remains ill-defined. The present study characterizes the clinicopathologic and molecular features of HER2-amplified ECs across all histologic subtypes. Retrospective analysis of our institutional cohort of 2,042 ECs subjected to targeted clinical massively parallel sequencing identified 77 (3.8%) cases with HER2 amplification, a group comprised of serous (n = 29), endometrioid (low-grade, n = 2, high-grade, n = 1) and clear cell (n = 4) carcinomas, carcinosarcomas (n = 18) and high-grade ECs with ambiguous features (HGEC, n = 23). A co-existing TP53 mutation was identified in 94% (72/77) of HER2-amplified ECs. Other recurrent genetic alterations included amplification of CCNE1 (22%) and ERBB3 (10%), FBXW7 mutations or deletions (13%), and mutations in PIK3CA (40%) and PPP2R1A (13%). The HER2 immunohistochemistry score was 2+ or 3+ for all evaluable cases (n = 61). Apart from carcinosarcomas, which often showed lower HER2 expression, particularly in the sarcomatous component, HER2 immunohistochemical staining pattern and intensity were similar across EC subtypes. Intratumor heterogeneity in HER2 expression was common and correlated with genetic heterogeneity as detected by fluorescence in-situ hybridization. These results demonstrate the frequent co-occurrence of HER2 amplification with TP53 mutation and high-grade histology, rather than being specific to serous carcinoma, per se. Overall, these findings suggest that HER2 targeted therapy may be more broadly applicable to all high-grade EC histotypes and consideration should be given to expanding therapeutic eligibility.