Solitary Fibrous Tumor of Breast and Axilla: Clinicopathological Profile of Five Tumors With Comparison of Risk Stratification Models.

Introduction: Solitary fibrous tumor (SFT) is a fibroblastic tumor with malignant potential that is underpinned by a recurrent inv12(q13q13)-derived NAB2::STAT6 fusion. Breast and axilla are uncommon locations for this entity. Methods: Records of two academic institutions were electronically searched for breast and axillary SFTs. Clinical and pathologic data were reviewed. Literature review for breast or axillary SFTs was performed. Present study and previously reported tumors were stratified using five SFT risk models: original and modified Demicco metastatic risk, Salas local recurrence risk, Salas metastatic risk, and Thompson local recurrence risk. Results: Five patients with breast or axillary SFT were identified. Median age was 49 years, and median follow-up (available for four patients) was 82 months. Three patients showed no evidence of disease, and one developed recurrence. Literature review identified 58 patients with breast or axillary SFT. Median age was 54 years, and median follow-up (available for 35 patients) was 24 months. Thirty-one patients showed no evidence of disease, three developed recurrence, and one developed metastasis. Original and modified Demicco models and Thompson model showed the highest sensitivity; original and modified Demicco models and Salas metastatic risk model demonstrated the highest specificity. Kaplan-Meier models were used to assess recurrence-free probability (RFP). Original and modified Demicco models predicted RFP when stratified by "low risk" and "moderate/intermediate and high risk" tumor, though sample size was small. Conclusions: While many SFTs of breast and axilla remain indolent, a subset may develop recurrence and rarely metastasize. The modified Demicco risk model demonstrated optimal performance characteristics.

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.

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.

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.

Quality Issues in Diagnostic Immunohistochemistry in Breast Pathology.

Immunohistochemistry techniques have been incorporated into surgical pathology for nearly a half-century and have since become intimately intertwined with its practice. In the realm of breast pathology, immunohistochemistry serves several purposes, including providing crucial prognostic and predictive data. Among its other applications, assessment of stromal invasion and establishment of mammary origin are crucial from a diagnostic standpoint. In these regards, sole reliance on immunohistochemistry may lead to misdiagnosis. In this review, we highlight pitfalls of immunohistochemistry commonly encountered in the practice of breast pathology and emphasize the importance of careful histopathological evaluation.

Clinical and Pathologic Features Associated With Invasive Breast Carcinoma With 2018 American Society of Clinical Oncology/College of American Pathologists In Situ Hybridization Group 2 Results (Human Epidermal Growth Factor Receptor 2 [HER2]/Chromosome 17 Centromere [CEP17] Ratio ≥2.0 and Average HER2 Copy Number <4.0).

CONTEXT.­: The American Society of Clinical Oncology/College of American Pathologists updated the human epidermal growth factor receptor 2 (HER2) breast carcinoma testing guideline in 2018 to address issues from uncommon HER2 fluorescence in situ hybridization (FISH) results. Based on the 2013 American Society of Clinical Oncology/College of American Pathologists guideline, cases wherein the HER2/chromosome 17 centromere (CEP17) ratio of 2.0 or more with an average HER2 copy number of less than 4.0 were considered in situ hybridization (ISH) positive. Under the 2018 guideline, such cases are classified as ISH Group 2 and are no longer considered eligible for anti-HER2 therapy when the corresponding HER2 immunohistochemistry result is 0, 1+, or 2+. OBJECTIVE.­: To assess the clinical, pathologic, and treatment aspects of patients with ISH Group 2 results. DESIGN.­: We retrospectively reviewed HER2 FISH results at our center between January 2012 and December 2014 and identified and characterized cases with ISH Group 2 results. RESULTS.­: Thirty-nine cases with ISH Group 2 results from 39 patients were reviewed. Twenty of 39 (51%) patients received anti-HER2 therapy. Patients treated with HER2-targeted therapy were less likely to have hormone receptor-positive tumors, compared with patients without anti-HER2 treatment, though not significantly (P = .30). The only significant difference between the 2 patient groups was receipt of cytotoxic chemotherapy treatment (P < .001). Overall, clinical outcome was similar between the 2 groups (P > .99). CONCLUSIONS.­: This retrospective study with median follow-up of at least 6 years shows patients with ISH Group 2 tumors had similar clinical outcomes, irrespective of HER2-targeted therapy. Further analysis in the prospective setting would provide valuable data that would potentially inform clinical decision making.

Risk of malignancy associated with diagnostic categories of the proposed World Health Organization International System for Reporting Pancreaticobiliary Cytopathology.

BACKGROUND: The World Health Organization (WHO) has proposed an updated international classification system for reporting pancreaticobiliary cytology. Substantial changes to the prior Papanicolaou Society of Cytopathology (PSC) system have been recommended. Chiefly, the "neoplastic: benign" and "neoplastic: other" categories have been replaced by 2 new categories-"pancreatic neoplasia-low-grade" (PaN-Low) and "pancreatic neoplasia-high-grade" (PaN-High)-stratifying neoplastic mucinous cysts by cytological atypia. Low-grade malignancies are placed in the "malignant" category and benign serous cystadenoma in the "benign/negative" category. Risk of malignancy (ROM) associated with the diagnostic categories of the WHO system has yet to be defined. METHODS: All patients who underwent endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) for a pancreatic lesion at a single institution from January 2016 to December 2016, prospectively classified using the PSC system, were reclassified using the WHO system. Absolute ROM was determined by histologic outcome and/or clinical follow-up of at least 6 months. RESULTS: A total of 334 EUS-FNA samples from 322 patients were reviewed and reclassified. Absolute ROM for the WHO system was 7.7% for "insufficient/inadequate/nondiagnostic" category, 1.0% for "benign/negative for malignancy," 28.0% for "atypical," 4.8% for "PaN-Low," 60.0% for "PaN-High," 100% for "suspicious for malignancy," and 100% for "malignant;" the absolute ROM for the same cohort using the PSC system was 7.7% for "nondiagnostic" category, 1.0% for "negative (for malignancy)," 28.0% for "atypical," 0.0% for "neoplastic: benign," 30.3% for "neoplastic: other," 100% for "suspicious (for malignancy)," and 100% for "positive or malignant." CONCLUSIONS: The WHO international system achieves improved stratification by associated ROM compared to the PSC system.

Papillary Breast Tumors: Continuing Controversies and Commentary on WHO's 2019 Criteria and Classification.

The category of papillary breast tumors includes a limited number of entities. Nonetheless, this relatively uncommon group of tumors seems to instigate a disproportionate degree of diagnostic disquiet. As a group, papillary breast tumors suffer from a relatively high rate of discordant interpretation. The latter is due to the inherent complexity of the lesions compounded by conflicting criteria as well as simmering controversies. For instance, "encapsulated" papillary carcinoma remains contentious with regards to whether these are noninvasive or not, and the assessment of the extent of the invasive versus noninvasive components in many solid papillary carcinomas can be problematic. The latest classification system of breast tumors enunciated by the World Health Organization (WHO), that is, Breast Tumors, which appeared in 2019, mainly sought to incorporate advances in basic and clinical sciences into diagnostic criteria for the entire spectrum of breast neoplasms-including papillary ones. The latter category of tumors is discussed at some length in Breast Tumors; however, it still appears to suffer from some lack of clarity in its subclassification. It is our intent in this communication to provide an overview of the controversies around papillary breast tumors, and offer comments on its coverage in Breast Tumors-so that any tangible or perceived ambiguities therein could be addressed in its next edition.

Assessing PD-L1 Expression Status Using Radiomic Features from Contrast-Enhanced Breast MRI in Breast Cancer Patients: Initial Results.

The purpose of this retrospective study was to assess whether radiomics analysis coupled with machine learning (ML) based on standard-of-care dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) can predict PD-L1 expression status in patients with triple negative breast cancer, and to compare the performance of this approach with radiologist review. Patients with biopsy-proven triple negative breast cancer who underwent pre-treatment breast MRI and whose PD-L1 status was available were included. Following 3D tumor segmentation and extraction of radiomic features, radiomic features with significant differences between PD-L1+ and PD-L1- patients were determined, and a final predictive model to predict PD-L1 status was developed using a coarse decision tree and five-fold cross-validation. Separately, all lesions were qualitatively assessed by two radiologists independently according to the BI-RADS lexicon. Of 62 women (mean age 47, range 31-81), 27 had PD-L1- tumors and 35 had PD-L1+ tumors. The final radiomics model to predict PD-L1 status utilized three MRI parameters, i.e., variance (FO), run length variance (RLM), and large zone low grey level emphasis (LZLGLE), for a sensitivity of 90.7%, specificity of 85.1%, and diagnostic accuracy of 88.2%. There were no significant associations between qualitative assessed DCE-MRI imaging features and PD-L1 status. Thus, radiomics analysis coupled with ML based on standard-of-care DCE-MRI is a promising approach to derive prognostic and predictive information and to select patients who could benefit from anti-PD-1/PD-L1 treatment.

PD-L1 Expression in Metaplastic Breast Carcinoma Using the PD-L1 SP142 Assay and Concordance Among PD-L1 Immunohistochemical Assays.

Immunotherapy for the treatment of programmed death-ligand 1 (PD-L1) positive locally advanced or metastatic triple negative breast cancer may benefit patients with metaplastic breast cancer (MpBC). Previous study of PD-L1 in MpBC scored tumor cells (TCs), different from Food and Drug Administration-approved scoring methods. We sought to define PD-L1 expression in MpBCs and to evaluate concordance of 3 PD-L1 assays. Primary, treatment naive MpBC treated at our Center from 1998 to 2019 were identified. PD-L1 expression was assessed using SP142, E1L3n, and 73-10. We evaluated PD-L1 expression on tumor infiltrating immune cells (IC) and also in TCs. For each assay, we scored PD-L1 expression using ≥1% IC expression according to the IMpassion130 trial criteria and using combined positive score (CPS) ≥10 according to the KEYNOTE-355 trial cutoff. A total of 42 MpBCs were identified. Most MpBC had PD-L1 positivity in ≥1% IC with all 3 assays (95%, 95%, 86%) in contrast to a maximum 71% with a CPS ≥10. PD-L1 IC expression was comparable between the SP142 and 73-10 assays and was lowest with E1L3n. PD-L1 TC expression was lowest using SP142. The overall concordance for IC scoring was 88% while 62% had concordant CPS. For each assay, the results of the 2 scoring algorithms were not interchangeable. The SP142 assay showed distinct expression patterns between IC (granular, dot-like) and TC (membranous) while 73-10 and E1L3n showed membranous and/or cytoplasmic expression in both IC and TC. Most MpBC in our cohort were positive for PD-L1 indicating eligibility for anti-PD-L1/programmed death-1 immunotherapy.

Interobserver Variation of PD-L1 SP142 Immunohistochemistry Interpretation in Breast Carcinoma: A Study of 79 Cases Using Whole Slide Imaging.

CONTEXT.­: The Ventana programmed death ligand-1 (PD-L1) SP142 immunohistochemical assay (IHC) is approved by the US Food and Drug Administration as the companion diagnostic assay to identify patients with locally advanced or metastatic triple-negative breast cancer for immunotherapy with atezolizumab, a monoclonal antibody targeting PD-L1. OBJECTIVE.­: To determine interobserver variability in PD-L1 SP142 IHC interpretation in invasive breast carcinoma. DESIGN.­: The pathology database was interrogated for all patients diagnosed with primary invasive, locally recurrent, or metastatic breast carcinoma on which PD-L1 SP142 IHC was performed from November 2018 to June 2019 at our institution. A subset of cases was selected using a computerized random-number generator. PD-L1 IHC was evaluated in stromal tumor-infiltrating immune cells using the IMpassion130 trial criteria, with positive cases defined as immunoreactivity in immune cells in 1% or more of the tumor area. IHC was interpreted on whole slide images by staff pathologists with breast pathology expertise. Interobserver variability was calculated using unweighted κ. RESULTS.­: A total of 79 cases were assessed by 8 pathologists. Interobserver agreement was substantial (κ = 0.727). There was complete agreement among all 8 pathologists in 62% (49 of 79) of cases, 7 pathologists or more in 84% (66 of 79) of cases, and 6 pathologists or more in 92% (73 of 79) of cases. In 4% (3 of 79) of cases, all of which were small biopsies, pathologists' interpretations were evenly split between scores of positive and negative. CONCLUSIONS.­: The findings show substantial agreement in PD-L1 SP142 IHC assessment of breast carcinoma cases among 8 pathologists at a single institution. Further study is warranted to define the basis for discrepant results.

Next-generation assessment of human epidermal growth factor receptor 2 gene (ERBB2) amplification status in invasive breast carcinoma: a focus on Group 4 by use of the 2018 American Society of Clinical Oncology/College of American Pathologists HER2 testing guideline.

AIMS: The American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) updated the testing guideline in 2018 to address issues arising from uncommon human epidermal growth factor receptor 2 (HER2) fluorescence in-situ hybridisation (FISH) results according to the 2013 guideline. Next-generation sequencing (NGS) may be used to better classify patients. The aim of this study was to assess the ERBB2 amplification status of invasive breast carcinoma with equivocal HER2 immunohistochemistry (IHC) results by using NGS, focusing on Group 4 (HER2/CEP17 ratio of <2.0; average HER2 signals/cell of ≥4.0 and <6.0). METHODS AND RESULTS: We retrospectively reviewed HER2 FISH and NGS data of HER2 IHC-equivocal breast carcinomas at our centre between January 2009 and September 2019, wherein all three assays were performed on the same tissue block, and compared HER2 FISH results, according to the 2018 ASCO/CAP guideline, and the ERBB2 amplification status determined with NGS. A total of 52 HER2 FISH and NGS results from 51 patients with HER2 IHC-equivocal breast carcinomas were reviewed. The cohort included eight cases classified as 2018 ASCO/CAP in-situ hybridisation Group 1, three classified as Group 2, three classified as Group 3, 14 classified as Group 4, and 24 classified as Group 5. Thirteen of 14 (92.9%) Group 4 (HER2-negative) cases were classified as ERBB2-non-amplified by the use of NGS; the discordant case was later classified as Group 1 with alternative sample FISH testing. NGS revealed no significant difference in somatic mutations or copy number alterations between Groups 4 and 5. CONCLUSIONS: Our NGS findings support the reclassification of HER2 FISH-equivocal cases as HER2-negative under the 2018 ASCO/CAP guideline.

Clinical and pathologic features associated with PD-L1 (SP142) expression in stromal tumor-infiltrating immune cells of triple-negative breast carcinoma.

The Ventana PD-L1 SP142 immunohistochemistry (IHC) assay is the FDA-approved companion diagnostic assay for atezolizumab therapy selection for patients with PD-L1-positive locally advanced or metastatic triple-negative breast carcinoma (TNBC). We aimed to elucidate clinical, pathologic, and molecular features associated with PD-L1 expression in TNBCs. Clinical, pathologic, and next-generation sequencing (NGS)-based molecular data for TNBCs tested with PD-L1 (SP142) IHC at our institution between 11/2018 and 12/2019 were retrieved and reviewed. PD-L1 positivity was defined as ≥1% IC staining. Patients with metastatic TNBC treated at first line with atezolizumab regimens were evaluated for treatment response and for time to treatment failure (TTF). Among 156 TNBCs, PD-L1 was positive in 47.4% of cases. Primary TNBCs were significantly more frequently PD-L1 positive, compared with recurrent/metastatic samples (p = 0.002). PD-L1-positive TNBCs had increased stromal IC, compared with PD-L1-negative samples (p < 0.001). The repertoire of somatic genetic alterations of PD-L1-positive and PD-L1-negative TNBCs was similar. Matched primary and recurrent/metastatic TNBC samples were available for eight patients, in whom four had discordant results. Thirty patients with metastatic TNBC were treated with atezolizumab regimens, with treatment failure occurring in 16 patients and a median TTF of 5.1 months in this early evaluation. The findings of this study show stromal ICs in primary TNBCs are more likely to show PD-L1 positivity than in recurrent or metastatic samples. This information should guide selection of samples suitable for testing. Further studies are needed to identify other features associated with PD-L1-positive breast carcinomas and clinical benefit of treatment.