ERBB2 Amplification and HER2 Expression in Salivary Duct Carcinoma: Evaluation of Scoring Guidelines and Potential for Expanded Anti-HER2 Therapy.

Salivary duct carcinoma (SDC) is aggressive with limited therapeutic options. A subset of SDC display human epidermal growth factor receptor 2 (HER2) protein overexpression by immunohistochemistry, and some show ERBB2 gene amplification. Guidelines for HER2 scoring are not firmly established. Recent advances in breast carcinoma have established a role for anti-HER2 therapies in lesions with low HER2 expression lacking ERBB2 amplification. Delineating HER2 staining patterns in SDC is critical for evaluating anti-HER2 treatments. In total, 53 cases of SDC resected at our institution between 2004 and 2020 were identified. Androgen receptor (AR) and HER2 immunohistochemistry and ERBB2 fluorescence in situ hybridization were performed in all cases. AR expression was scored for percentage positive cells and categorized as positive (>10% of cells), low positive (1%-10%), or negative (<1%). HER2 staining levels and patterns were recorded, scored using 2018 ASCO/CAP guidelines, and categorized into HER2-positive (3+ or 2+ with ERBB2 amplification), HER2-low (1+ or 2+ without ERBB2 amplification), HER2-very low (faint staining in <10% of cells), or HER2-absent types. Clinical parameters and vital status were recorded. Median age was 70 years, with a male predominance. ERBB2-amplified tumors (11/53; 20.8%) presented at lower pT stages (pTis/pT1/pT2; P = .005, Fisher exact test) and more frequently had perineural invasion (P = .007, Fisher exact test) compared with ERBB2 nonamplified tumors; no other pathologic features differed significantly by gene amplification status. In addition, 2+ HER2 staining by 2018 ASCO/CAP criteria was most common (26/53; 49%); only 4 cases (8%) were HER2-absent status; 3+ HER2 staining was found in 9 tumors, and all were ERBB2 amplified. Six patients with HER2-expressing tumors received trastuzumab therapy, including 2 with ERBB2-amplified tumors. Overall survival and recurrence-free survival did not differ significantly based on ERBB2 status. This work suggests that 2018 ASCO/CAP guidelines for HER2 evaluation in breast carcinoma could be applied to SDC. Our findings also show broad overexpression of HER2 in SDC raising the possibility that more patients may benefit from anti-HER2-directed therapies.

Low-grade adenosquamous carcinoma of the breast: a clinical, morphological and immunohistochemical analysis of 25 patients.

AIMS: Due to its rarity and non-specific clinical and pathological features, low-grade adenosquamous carcinoma (LGASC) of the breast continues to pose diagnostic challenges. Unlike other triple-negative breast carcinomas, LGASC tends to have an indolent clinical behaviour. It is essential to recognise this lesion for accurate diagnosis and appropriate management. METHODS AND RESULTS: Twenty-five cases of LGASC were identified in our archives and collaborating institutes. Cases of LGASC with dominant coexisting other type carcinomas were excluded. We studied the clinical presentation, morphological features, patterns of the commonly used immunohistochemical stains and follow-up. In our cohort, LGASC was commonly located at the outer aspect of the breast and associated with intraductal papilloma. The morphology of LGASC is characterised by infiltrating small glands and nests with variable squamous differentiation. We also found cuffing desmoplastic (fibrolamellar) stromal change in 75% of patients and peripheral lymphocytic aggregates in 87.5% of patients. P63 and smooth muscle myosin (SMM) were the most common myoepithelial markers used to assist in diagnosis. P63 often stained peripheral tumour cells surrounding invasive glands (circumferential staining in 80% of the cases), mimicking myoepithelial cells. It also stained the small nests with squamous differentiation. However, SMM was negative in 63% of the cases. The vast majority of our cases were triple-negative; only a few had focal and weak expressions of ER and PR. One patient who did not have excision developed lymph node metastasis. Most patients underwent excision or mastectomy with negative margins as surgical treatment; there were no recurrences or metastases in these patients with clinical follow-ups up to 108 months. CONCLUSIONS: LGASC has some unique, although not entirely specific, morphological features and immunohistochemical staining patterns. Fibrolamellar stromal change, peripheral lymphocytic aggregates and variable staining of p63 and SMM are valuable features to facilitate the diagnosis.

Evaluating Low HER2 Status in Invasive Breast Carcinoma via HER2 Immunohistochemistry, with HER2 FISH Correlation: A Cohort of 112 Patients.

Introduction: Recent trials demonstrated clinically significant benefits in HER2-nonamplified breast cancer with HER2-low expression using novel anti-HER2 antibody-drug conjugates. Thus, HER2-low breast cancer was proposed as a separate diagnostic entity. Herein, we reclassify HER2-negative cancers according to the new HER2-low category using a modified system and further investigate HER2-very-low expression. Methods: 114 HER2 immunohistochemistry (IHC)-negative invasive breast tumors were identified from the pathology database of Mayo Clinic, Jacksonville, FL, between January 2019 and August 2022. Two blinded breast pathologists (BP) independently rescored HER2 IHC slides at 200x and 400x magnification. Discordant cases between the two BPs were rescored together. The most recent 2018 ASCO/CAP HER2 scoring criteria were used. HER2 (0) was subdivided into HER2 (absent) and HER2 (very low). HER2 FISH testing was performed in all cases. Results: The cohort comprised of 38 (33.3%) HER2 (0) and 76 (66.7%) HER2 (1+) tumors. The first round of rescoring at 200x and 400x magnification resulted in 17 (14.9%) HER2 (absent), 31 (27.2%) HER2 (very low), and 64 (56.2%) HER2 (1+) and 2 (1.8%) HER2 (2+) tumors by BP1 and 20 (17.5%) HER2 (absent), 33 (28.9%) HER2 (very low), and 61 (53.5%) HER2 (1+) tumors by BP2. The combined final rescoring by BP1 and BP2 was as follows: 15 (13.2%) HER2 (absent), 35 (30.7%) HER2 (very low), 63 (55.3%) HER2 (1+), and 1 (0.9%) HER2 (2+) cases. A comparison of the first round of rescoring between two BPs showed substantial agreement with Cohen's kappa value of 0.67. Both comparisons of first rescoring by BP1 and by BP2 to combined final rescoring showed almost perfect agreement with Cohen's kappa value of 0.83.Follow-up FISH studies showed one amplified tumor. Conclusion: Our data support the need for finer granularity, classification, and understanding of HER2-low breast cancers. We also show that reproducibility between trained BP can be obtained, albeit with scoring at high power and low threshold for showing challenging interpretations.

Amyloid in the breast: retrospective review with clinicopathological and radiological correlation of 32 cases from a single institution.

AIMS: Mammary amyloid is an uncommon and easily overlooked pathological diagnosis with ambivalent presentation. Herein, we delineate the clinicopathological and radiographic characteristics of mammary amyloid. METHODS AND RESULTS: The Department of Pathology database was searched from 1993 to 2019 for keywords 'breast' and 'amyloid', yielding 32 cases from 23 patients, including consultation cases. All patients were female, age range = 52-81 (mean = 67.4 years). The left breast was involved more than the right (43 versus 33%, respectively); bilateral amyloid involvement was also present (24%). Amyloid was most often associated with a benign histopathological diagnosis (57%), lymphoma in 39% [all B cell lymphomas; five of nine were mucosa-associated lymphoid tissue (MALT) lymphoma] and rarely with a concurrent epithelial malignancy (invasive lobular carcinoma, 4%). Of the 14 patients with available clinical history, amyloid presented as a mass clinically or radiographically (six patients, 43%), as microcalcifications (five patients, 36%), and only occasionally as an asymmetry (14%) or fibroglandular density (7%). Microscopic examination detected microcalcifications in an additional nine cases (total 14 patients; 44% of the cohort). Interestingly, one patient had concurrent epithelial and haematological malignancy and amyloid within an axillary lymph node. Co-morbidities included autoimmune diseases and multiple myeloma. CONCLUSION: The majority of mammary amyloid cases are associated with benign histopathological findings, while imaging most frequently noted microcalcifications or mass lesions. To avoid overlooking amyloid as simply fat necrosis or fibroelastotic stromal change, a low threshold for performing ancillary stains should be considered in elderly women with benign core needle findings performed for mass lesions or microcalcifications.

A rare case of syringocystadenocarcinoma papilliferum of the breast: An institutional retrospective case review and brief literature review.

Syringocystadenocarcinoma papilliferum (SCACP) is a rare cutaneous adnexal tumor thought to originate from its benign counterpart, syringocystadenoma papilliferum. These tumors are predominantly located on the head and neck with their location on the breast extraordinarily reported; mammary localization poses a great diagnostic dilemma to the practicing pathologist. Herein, we report an unusual case of an 85-year-old woman with an outside diagnosis on a core needle biopsy of metaplastic mammary carcinoma. Upon consultative review of the partial mastectomy specimen, SCACP was identified. Herein, we review SCACP and the diagnostic challenge it poses, especially when localized to the breast. Furthermore, we perform a retrospective review of institutional pathology reports and identified four additional cases of SCACP diagnosed at our institution within the last decade. Finally, we briefly review the literature of SCACP. The entity of SCACP should be well known to pathologists to avoid misdiagnosis.

Rare Initial Manifestation of Lupus as Lobular Panniculitis of the Breast-A Case Report and Review of the Literature.

ABSTRACT: Lupus mastitis is a rare complication of systemic or discoid lupus erythematosus with an uncommon initial presentation when limited to the breast. In this article, we report a 42-year-old woman who presented with constant pain and tenderness in her breasts. Ultrasound imaging of the left breast revealed a 14-mm oval mass, suspicious for malignancy; a needle core biopsy was performed. Sections showed necrosis of the fat lobules with associated mixed nodular lymphoplasmacytic aggregates. Karyorrhectic debris, fibrinoid necrosis of small vessels, and microcalcifications were all present while the background breast parenchyma was unremarkable. The diagnosis of lupus mastitis was rendered. Subsequent serology showed negative dsDNA but positive antinuclear antibodies, C4, and anti -Sjögren';s-syndrome-related antigen A antibodies. Clinical features of active systemic disease were not identified at the patient's follow-up dermatology appointment 1 month after the biopsy, and she elected management for her nodules with steroids. To the best of our knowledge, only 40 other cases of lupus mastitis have been reported in the English literature, of which 25 presented as a mass and only in 6 lupus mastitis of the breast was the initial presentation. In conclusion, we bring much needed awareness to lupus mastitis as the first presentation of disease.

Immediate Release of Gastrin-Releasing Peptide Mediates Delayed Radiation-Induced Pulmonary Fibrosis.

Radiation-induced pulmonary fibrosis (RTPF) is a progressive, serious condition in many subjects treated for thoracic malignancies or after accidental nuclear exposure. No biomarker exists for identifying the irradiated subjects most susceptible to pulmonary fibrosis (PF). Previously, we determined that gastrin-releasing peptide (GRP) was elevated within days after birth in newborns exposed to hyperoxia who later developed chronic lung disease. The goal of the current study was to test whether radiation (RT) exposure triggers GRP release in mice and whether this contributes to RTPF in vivo. We determined urine GRP levels and lung GRP immunostaining in mice 0 to 24 after post-thoracic RT (15 Gy). Urine GRP levels were significantly elevated between 24 hours post-RT; GRP-blocking monoclonal antibody 2A11, given minutes post-RT, abrogated urine GRP levels by 6 to 12 hours and also altered phosphoprotein signaling pathways at 24 hours post-RT. Strong extracellular GRP immunostaining was observed in lung at 6 hours post-RT. Mice given one dose of GRP monoclonal antibody 2A11 24 hours post-RT had significantly reduced myofibroblast accumulation and collagen deposition 15 weeks later, indicating protection against lung fibrosis. Therefore, elevation of urine GRP could be predictive of RTPF development. In addition, transient GRP blockade could mitigate PF in normal lung after therapeutic or accidental RT exposure.

Tumour-infiltrating lymphocytes in ductal carcinoma in situ (DCIS)-assessment with three different methodologies and correlation with Oncotype DX DCIS Score.

AIMS: Tumour-infiltrating lymphocytes (TILs) are prognostic in invasive breast cancer; however, their prognostic significance in ductal carcinoma in situ (DCIS) has not been established. The Oncotype DX (ODX) Breast DCIS Score test is a genomic assay used to predict the local recurrence risk. The aims of this study were to quantify TILs in DCIS by the use of three methodologies, and correlate them with the ODX DCIS Score. METHODS AND RESULTS: We studied 97 DCIS cases, all with an ODX DCIS Score. Cases with a low ODX DCIS Score were considered as one group, and those with an intermediate/high ODX Score were considered together. TILs were quantified on haematoxylin and eosin-stained slides. The methodologies used to quantify TILS included assessment of stromal TILs, assessment of touching TILs, and assessment of circumferential TILS. In cases with >5% stromal TILS, the percentage of stromal TILS was considered to be high. In cases with a mean number of more than five touching TILs per DCIS duct, TILs were considered to be present. The ODX DCIS Score was intermediate/high in 27 (28%) cases and low in 70 (72%) cases. There were >5% stromal TILs in 33 (34%) cases, and more than five touching TILs per DCIS duct in 15 (15%) cases; circumferential TILs were present in nine (9%) cases. In univariate analysis, a low ODX DCIS Score showed significant associations with absent touching TILS (P = 0.027), stromal TILs < 5% (P = 0.031), and absent circumferential TILs (P = 0.002). In logistic regression analysis adjusted for necrosis and nuclear grade, touching TILs and circumferential TILs showed significant associations with the ODX DCIS Score, whereas stromal TILs did not. CONCLUSIONS: Our results suggest that both the presence of TILs and the spatial arrangement of TILs or close proximity of TILs to DCIS, and TILs touching or encircling DCIS, may be predictive of recurrence.

Subungual leiomyoma in the left thumb of a 16-year-old female.

Cutaneous leiomyomata, which are benign smooth muscle neoplasms, commonly present as dermal-based nodules or papules with smooth borders and firm consistency. Digital, particularly subungual leiomyomata are quite rare. A 16-year-old female presented to nail clinic complaining of discoloration of the lunula of the left thumbnail for 2.5 months. On initial examination, a pink longitudinal band was present in the center of the nail plate, with yellow discoloration and distal onycholysis. The patient had only mild tenderness with firm palpation, and did not recall trauma of the area. A nail matrix biopsy was performed to determine the etiology of the lesion. Microscopic examination demonstrated a well-demarcated dermal-based spindle-cell fascicular proliferation. Bland cells exhibited eosinophilic cytoplasm and elongate nuclei with blunt ends and minimal cytologic atypia. Prominent nucleoli, mitoses or necrosis were not appreciated. Immunohistochemical stains for smooth muscle actin and caldesmon highlighted the cells. Contrarily, S-100, epithelial membrane antigen, p63, factor XIIIa, CD34, CD68 and p75 were all negative. Ki-67 showed a low proliferative index. The immunoprofile combined with the morphologic features were interpreted as subungual leiomyoma. Subungual leiomyoma is a very rare diagnosis. We seek to bring awareness and expedite the diagnosis in patients with this lesion.

Multiple Clustered Dermatofibromas Associated With Pulmonary Arterial Hypertension.

BACKGROUND: Dermatofibromas (DFs) are common, benign, fibrohistiocytic tumors of the skin. Clinically, if they present in a rapid succession, they are termed multiple eruptive DFs. When they arise in a localized distribution, they are termed multiple clustered dermatofibromas (MCDFs). These DF variants are rare, and the subtype of multiple eruptive DFs has been associated with autoimmune diseases, hypertriglyceridemia, pregnancy, HIV, and primary pulmonary hypertension. Conversely, there is a paucity of published clinical associations with MCDF. METHODS: A 23-year-old white woman with pulmonary arterial hypertension presented with a 7-year history of multiple, asymptomatic, firm, brown, and violaceous papules clustered on the right hip. RESULTS: Histopathologic examination of the biopsies demonstrated acanthotic epidermis, proliferation of cytologically bland fibrohistiocytic spindle cells in a fascicular pattern in the dermis, and collagen trapping on the periphery. Immunohistochemistry was focally positive for factor XIIIa and negative for CD34, thus supporting the clinical diagnosis of MCDF. CONCLUSIONS: A case of MCDF associated with pulmonary arterial hypertension is presented. To date, there have been greater than 25 reported cases of MCDF, but only one other publication has described an associated systemic comorbidity.

An Extraordinary Association of Glomus Tumor and Pacinian Hyperplasia in the Hand of a Female Patient.

BACKGROUND: Glomus tumor is a benign neoplasm of the glomus body, a neuromyoarterial structure that regulates temperature and pressure in the cutaneous vasculature. Approximately 1%-4.5% of glomus tumors present in the hands of females; of these, 65% are seen in the subungual region of the index and long fingers. Pacinian hyperplasia is a benign lesion of the Pacinian corpuscle, a mechanoreceptor located in the subcutis of the hands and feet. METHODS: A 65-year-old woman with a history of hand trauma and a 1-year chief complaint of tingling, pain, and burning sensations in her proximal thumb underwent exploration of the digital nerve after an x-ray and 2 magnetic resonance imaging examinations failed to detect a mass. Two lesions immediately adjacent to each other were excised. RESULTS: Microscopic examination showed Pacinian hyperplasia, and a second proliferation of solid epithelioid cells related to benign blood vessels. Immunohistochemistry confirmed the epithelioid cells to be strongly positive for smooth muscle actin, CD34, and type 4 collagen, which is consistent with the phenotype of a glomus tumor. The cells were negative for S100 protein. CONCLUSIONS: The association of glomus tumor with Pacinian hyperplasia has rarely been reported in the literature. We present another rare case to bring awareness to this differential diagnostic consideration.

Silicone granuloma with intact breast implants: A case report.

Silicone granuloma formation is a potential complication of silicone implant rupture. Breast magnetic resonance imaging (MRI) is a useful diagnostic tool to assess implant integrity and complications; however, there can be overlap in the enhancement pattern of silicone granuloma and malignancy. We present the case of an 85 year old with suspicious axillary masses on clinical exam for which MRI was recommended. MRI demonstrated enhancing masses in the right axilla that were suspicious for malignancy and biopsy was ultimately performed. This case discusses the use of inversion recovery sequences on MRI, as well as ultrasound, to differentiate malignancy from silicone granuloma formation to prevent unnecessary biopsies.

Rare Presentation of Papillary Carcinoma Within a Sentinel Lymph Node in a Patient With Ductal Carcinoma in Situ of the Breast: A Challenging but Useful Case Report Discussion Regarding Displacement or True Metastasis?

Papillary carcinoma of the breast is a rare histologic subtype of invasive breast cancer. In contrast, ductal carcinoma in situ (DCIS) is a noninvasive, nonobligate precursor to invasive mammary carcinoma, confined within the terminal duct lobular unit of the breast and surrounded by an intact myoepithelial cell layer at the stromal/epithelial interface. We present an unusual case in which a patient with only DCIS of the breast exhibited papillary carcinoma within a sentinel lymph node, leading to questions about the origin of the lymph node lesion-whether it represents a true metastasis or iatrogenic displacement during diagnostic procedures. This case underscores the diagnostic challenges and clinical implications associated with such rare presentations.

Metastatic Non-Small Cell Lung Cancer Mimicking Metaplastic Breast Cancer: A Case Report.

NGS used to diagnose and treat NSCLC patient with initial concern for metaplastic breast cancer.

Identification of Glandular (Acinar)/Tubule Formation in Invasive Carcinoma of the Breast: A Study to Determine Concordance Using the World Health Organization Definition.

CONTEXT.­: The Nottingham Grading System (NGS) developed by Elston and Ellis is used to grade invasive breast cancer (IBC). Glandular (acinar)/tubule formation is a component of NGS. OBJECTIVE.­: To investigate the ability of pathologists to identify individual structures that should be classified as glandular (acinar)/tubule formation. DESIGN.­: A total of 58 hematoxylin-eosin photographic images of IBC with 1 structure circled were classified as tubules (41 cases) or nontubules (17 cases) by Professor Ellis. Images were sent as a PowerPoint (Microsoft) file to breast pathologists, who were provided with the World Health Organization definition of a tubule and asked to determine if a circled structure represented a tubule. RESULTS.­: Among 35 pathologists, the κ statistic for assessing agreement in evaluating the 58 images was 0.324 (95% CI, 0.314-0.335). The median concordance rate between a participating pathologist and Professor Ellis was 94.1% for evaluating 17 nontubule cases and 53.7% for 41 tubule cases. A total of 41% of the tubule cases were classified correctly by less than 50% of pathologists. Structures classified as tubules by Professor Ellis but often not recognized as tubules by pathologists included glands with complex architecture, mucinous carcinoma, and the "inverted tubule" pattern of micropapillary carcinoma. A total of 80% of participants reported that they did not have clarity on what represented a tubule. CONCLUSIONS.­: We identified structures that should be included as tubules but that were not readily identified by pathologists. Greater concordance for identification of tubules might be obtained by providing more detailed images and descriptions of the types of structures included as tubules.

Cholesterol granuloma of the breast: A case report.

Cholesterol granuloma of the breast is a rare entity that can be indistinguishable from cancer on physical exam and imaging. We present the case of a 58-year-old woman who developed a new enhancing mass on high-risk screening magnetic resonance imaging (MRI). Interestingly, this mass developed in the same area as a previously noted benign-appearing inflammatory cyst that had been decreasing in size on MRI and mammogram over many years. Ultrasound-guided biopsy was performed which revealed cholesterol granuloma. We will discuss the nonspecific imaging findings and the characteristic histopathological features that confirm diagnosis.

Encapsulated papillary carcinoma of the breast: A case report.

Breast malignancies diagnosed from screening mammography most commonly present as a new or enlarging lesion at the time of diagnosis. We present the unusual case of an encapsulated papillary carcinoma that demonstrated decreasing size on mammogram over several subsequent years. We review the unique imaging and histologic findings of papillary carcinoma that make this imaging conundrum possible.

Re-Classification with Outcome Correlation of Previously Diagnosed Malignant Phyllodes Tumors Applying the 2016 Consensus Guidelines.

Background. Classification of phyllodes tumors is challenging due unclear diagnostic criteria, recently addressed by consensus review criteria. Herein, we reviewed all malignant phyllodes tumor resections and reclassified them based on the consensus guidelines, correlating with outcome. We hypothesize that application of criteria would result in a significant proportion being "down-graded" to either borderline or benign phyllodes tumor. Methods. Primary resections of malignant phyllodes tumor were reviewed by four AP board-certified, breast fellowship-trained pathologists. Morphologic variables delineated in consensus guidelines (ie stromal cellularity, cellular atypia, tumor border, presence of heterologous elements, presence of stromal overgrowth) were evaluated. Following review, cases were reclassified as benign, borderline, or malignant. Results. Upon reclassification, 20% (5/20) cases were "down-graded" to borderline phyllodes tumor while 80% (15/20) remained malignant phyllodes tumor. Two morphologic features were statistically significant including broadly infiltrating tumor border in 80% (12/15) of malignant phyllodes tumors compared to none in borderline phyllodes tumor (0/5) (p = 0.004) and stromal overgrowth in 67% (10/15) of malignant phyllodes tumor compared to none in borderline phyllodes tumors (0/5) (p = 0.03). Upon review of the pathology reports, 30% (6/20) contained all 5 histomorphologic variables delineated in the consensus review criteria. Malignant phyllodes tumor resulted in five cases with recurrence (33.3%, 5/15) and three cases with metastases (20.0%, 3/15) and borderline phyllodes tumor resulted in one case with recurrence (20.0%, 1/5) and no metastases (0/5). Conclusion. The consensus guidelines for phyllodes tumor are useful for subclassification. We hypothesize that standardize reporting of the histomorphologic variables may lead to better consensus.

HER2 IHC Expression and Gene Amplification in p53-aberrant High-grade Endometrial Endometrioid Carcinoma Suggests That This Population May Benefit From HER2 Testing and Targeted Therapy.

Among gynecologic cancers, uterine serous carcinoma (USC) has been shown to be human epidermal growth factor receptor 2 (HER2) amplified and trastuzumab has been included in the recent National Comprehensive Cancer Network (NCCN) guidelines for treatment of advanced stage or recurrent USC with HER2 overexpression/amplification. There is limited literature suggesting that a subset of high-grade endometrioid carcinomas with aberrant p53 expression may also be HER2 amplified and these patients could benefit from the addition of targeted therapy. We identified 59 p53-aberrant (mismatch repair proficient) FIGO 3 endometrioid carcinomas of the uterus. HER2 immunohistochemistry was performed in all 59 tumors and HER2 fluorescence in situ hybridization (FISH) was performed in 52 of the 59 cases. Four of the 59 cases were HER2 3+ by immunohistochemistry (6.7%), using the American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) 2007, 2013, and 2018 criteria. HER2 FISH was performed in 3 of the 4 cases and was amplified in all 3. Nine, 8, and 7 tumors showed 2+ HER2 staining when applying 2018, 2013, and 2007 criteria, respectively, FISH was performed in 7 tumors and none were amplified. An additional 4 cases did not perfectly meet the 2018 ASCO/CAP criteria but were assigned a score of 2+, none were amplified by HER2 FISH. The remaining 42 cases showed 1+ or no staining for HER2, FISH was successfully performed in 38 tumors and none showed amplification. Approximately half of the tumors fulfilled criteria for HER2-low or HER2-very low (10 HER2-low and 20 HER2-very low). Our data shows that a subset of p53-aberrant high-grade endometrial endometrioid carcinoma express HER2 and these patients may benefit from the addition of targeted therapy. The role of targeted therapy in HER2-low gynecologic carcinoma is currently unexplored.