Comprehensive Molecular Portraits of Invasive Lobular Breast Cancer.

Invasive lobular carcinoma (ILC) is the second most prevalent histologic subtype of invasive breast cancer. Here, we comprehensively profiled 817 breast tumors, including 127 ILC, 490 ductal (IDC), and 88 mixed IDC/ILC. Besides E-cadherin loss, the best known ILC genetic hallmark, we identified mutations targeting PTEN, TBX3, and FOXA1 as ILC enriched features. PTEN loss associated with increased AKT phosphorylation, which was highest in ILC among all breast cancer subtypes. Spatially clustered FOXA1 mutations correlated with increased FOXA1 expression and activity. Conversely, GATA3 mutations and high expression characterized luminal A IDC, suggesting differential modulation of ER activity in ILC and IDC. Proliferation and immune-related signatures determined three ILC transcriptional subtypes associated with survival differences. Mixed IDC/ILC cases were molecularly classified as ILC-like and IDC-like revealing no true hybrid features. This multidimensional molecular atlas sheds new light on the genetic bases of ILC and provides potential clinical options.

Dataset for reporting of the invasive carcinoma of the breast: recommendations from the International Collaboration on Cancer Reporting (ICCR).

BACKGROUND AND OBJECTIVES: Current national or regional guidelines for the pathology reporting on invasive breast cancer differ in certain aspects, resulting in divergent reporting practice and a lack of comparability of data. Here we report on a new international dataset for the pathology reporting of resection specimens with invasive cancer of the breast. The dataset was produced under the auspices of the International Collaboration on Cancer Reporting (ICCR), a global alliance of major (inter-)national pathology and cancer organizations. METHODS AND RESULTS: The established ICCR process for dataset development was followed. An international expert panel consisting of breast pathologists, a surgeon, and an oncologist prepared a draft set of core and noncore data items based on a critical review and discussion of current evidence. Commentary was provided for each data item to explain the rationale for selecting it as a core or noncore element, its clinical relevance, and to highlight potential areas of disagreement or lack of evidence, in which case a consensus position was formulated. Following international public consultation, the document was finalized and ratified, and the dataset, which includes a synoptic reporting guide, was published on the ICCR website. CONCLUSIONS: This first international dataset for invasive cancer of the breast is intended to promote high-quality, standardized pathology reporting. Its widespread adoption will improve consistency of reporting, facilitate multidisciplinary communication, and enhance comparability of data, all of which will help to improve the management of invasive breast cancer patients.

A dedicated structured data set for reporting of invasive carcinoma of the breast in the setting of neoadjuvant therapy: recommendations from the International Collaboration on Cancer Reporting (ICCR).

AIMS: The International Collaboration on Cancer Reporting (ICCR), a global alliance of major (inter-)national pathology and cancer organisations, is an initiative aimed at providing a unified international approach to reporting cancer. ICCR recently published new data sets for the reporting of invasive breast carcinoma, surgically removed lymph nodes for breast tumours and ductal carcinoma in situ, variants of lobular carcinoma in situ and low-grade lesions. The data set in this paper addresses the neoadjuvant setting. The aim is to promote high-quality, standardised reporting of tumour response and residual disease after neoadjuvant treatment that can be used for subsequent management decisions for each patient. METHODS: The ICCR convened expert panels of breast pathologists with a representative surgeon and oncologist to critically review and discuss current evidence. Feedback from the international public consultation was critical in the development of this data set. RESULTS: The expert panel concluded that a dedicated data set was required for reporting of breast specimens post-neoadjuvant therapy with inclusion of data elements specific to the neoadjuvant setting as core or non-core elements. This data set proposes a practical approach for handling and reporting breast resection specimens following neoadjuvant therapy. The comments for each data element clarify terminology, discuss available evidence and highlight areas with limited evidence that need further study. This data set overlaps with, and should be used in conjunction with, the data sets for the reporting of invasive breast carcinoma and surgically removed lymph nodes from patients with breast tumours, as appropriate. Key issues specific to the neoadjuvant setting are included in this paper. The entire data set is freely available on the ICCR website. CONCLUSIONS: High-quality, standardised reporting of tumour response and residual disease after neoadjuvant treatment are critical for subsequent management decisions for each patient.

NCCN Guidelines® Insights: Breast Cancer, Version 4.2023.

The NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines) for Breast Cancer address all aspects of management for breast cancer. The treatment landscape of metastatic breast cancer is evolving constantly. The therapeutic strategy takes into consideration tumor biology, biomarkers, and other clinical factors. Due to the growing number of treatment options, if one option fails, there is usually another line of therapy available, providing meaningful improvements in survival. This NCCN Guidelines Insights report focuses on recent updates specific to systemic therapy recommendations for patients with stage IV (M1) disease.

Breast Cancer, Version 3.2022, NCCN Clinical Practice Guidelines in Oncology.

The therapeutic options for patients with noninvasive or invasive breast cancer are complex and varied. These NCCN Clinical Practice Guidelines for Breast Cancer include recommendations for clinical management of patients with carcinoma in situ, invasive breast cancer, Paget disease, phyllodes tumor, inflammatory breast cancer, and management of breast cancer during pregnancy. The content featured in this issue focuses on the recommendations for overall management of ductal carcinoma in situ and the workup and locoregional management of early stage invasive breast cancer. For the full version of the NCCN Guidelines for Breast Cancer, visit NCCN.org.

Prognostic and predictive parameters in breast pathology: a pathologist's primer.

The pathologist's role in the breast cancer treatment team has evolved from rendering a diagnosis of breast cancer, to providing a growing list of prognostic and predictive parameters such that individualized treatment decisions can be made based on likelihood of benefit from additional treatments and potential benefit from specific therapies. In all stages, ER and HER2 status help segregate breast cancers into treatment groups with similar outcomes and treatment response rates, however, traditional pathologic parameters such as favorable histologic subtype, size, lymph node status, and Nottingham grade also have remained clinically relevant in early stage disease decision-making. This is especially true for the most common subtype of breast cancer; ER positive, HER2 negative disease. For this same group of breast cancers, an ever-expanding list of gene-expression panels also can provide prediction and prognostication about potential chemotherapy benefit beyond standard endocrine therapies, with the 21-gene Recurrence Score, currently the only prospectively validated predictive test for this purpose. In the more aggressive ER-negative cancer subtypes, response to neoadjuvant therapy and` the extent of tumor infiltrating lymphocytes (TILs) are more recently recognized powerful prognostic parameters, and clinical guidelines now offer additional treatment options for those high-risk patients with residual cancer after standard neoadjuvant therapy. In stage four disease, predictive tests like germline BRCA status, tumor PIK3CA mutation status (in ER+ metastatic disease) and PDL-1 status (in triple negative metastatic disease) are now used to determine additional new treatment options. The objective of this review is to describe the latest in prognostic and predictive parameters in breast cancer as they are relevant to standard pathology reporting and how they are used in breast cancer clinical treatment decisions.

Nodular fasciitis of the breast: clinicopathologic and molecular characterization with identification of novel USP6 fusion partners.

Nodular fasciitis is a benign, self-limited, pseudosarcomatous neoplasm that can mimic malignancy due to its rapid growth, cellularity, and mitotic activity. Involvement of the breast is rare and diagnosis on biopsy can be challenging. In this largest series to date, we examined the clinicopathologic and molecular characteristics of 12 cases of nodular fasciitis involving the breast/axilla. All patients were female, with a median age of 32 years (range 15-61). The lesions were 0.4 to 5.8 cm in size (median 0.8). All cases presented as palpable masses, and two patients had overlying skin retraction. Microscopically, lesions were relatively well-circumscribed nodular masses of bland myofibroblastic spindle cells within a variably myxoid stroma. Infiltrative growth into adipose tissue or breast epithelium was frequent. Mitotic figures were present in all cases, ranging from 1 to 12 per 10 high-power fields (median 3). Immunohistochemically, all cases expressed smooth muscle actin and were negative for pan-cytokeratin, p63, desmin, CD34, and nuclear beta-catenin. Targeted RNA sequencing performed on 11 cases identified USP6 gene fusions in eight; one additional case was positive by break-apart fluorescence in situ hybridization. The common MYH9-USP6 rearrangement was detected in four cases; another case had a rare alternative fusion with CTNNB1. Three cases harbored novel USP6 gene fusions involving NACA, SLFN11, or LDHA. All fusions juxtaposed the promoter region of the 5' partner gene with the full-length coding sequence of USP6. Outcome data were available for eight patients; none developed recurrence or metastasis. Five patients elected for observation without immediate excision, and self-resolution of the lesions was reported in three cases. Albeit uncommon, nodular fasciitis should be considered in the differential diagnosis of breast spindle cell lesions. A broad immunohistochemical panel to exclude histologic mimics, including metaplastic carcinoma, is important. Confirmatory detection of USP6 rearrangements can aid in classification, with potential therapeutic implications.

Quantification of Human Epidermal Growth Factor Receptor 2 by Immunopeptide Enrichment and Targeted Mass Spectrometry in Formalin-Fixed Paraffin-Embedded and Frozen Breast Cancer Tissues.

BACKGROUND: Conventional HER2-targeting therapies improve outcomes for patients with HER2-positive breast cancer (BC), defined as tumors showing HER2 protein overexpression by immunohistochemistry and/or ERBB2 gene amplification determined by in situ hybridization (ISH). Emerging HER2-targeting compounds show benefit in some patients with neither HER2 protein overexpression nor ERBB2 gene amplification, creating a need for new assays to select HER2-low tumors for treatment with these compounds. We evaluated the analytical performance of a targeted mass spectrometry-based assay for quantifying HER2 protein in formalin-fixed paraffin-embedded (FFPE) and frozen BC biopsies. METHODS: We used immunoaffinity-enrichment coupled to multiple reaction monitoring-mass spectrometry (immuno-MRM-MS) to quantify HER2 protein (as peptide GLQSLPTHDPSPLQR) in 96 frozen and 119 FFPE BC biopsies. We characterized linearity, lower limit of quantification (LLOQ), and intra- and inter-day variation of the assay in frozen and FFPE tissue matrices. We determined concordance between HER2 immuno-MRM-MS and predicate immunohistochemistry and ISH assays and examined the benefit of multiplexing the assay to include proteins expressed in tumor subcompartments (e.g., stroma, adipose, lymphocytes, epithelium) to account for tissue heterogeneity. RESULTS: HER2 immuno-MRM-MS assay linearity was ≥103, assay coefficient of variation was 7.8% (FFPE) and 5.9% (frozen) for spiked-in analyte, and 7.7% (FFPE) and 7.9% (frozen) for endogenous measurements. Immuno-MRM-MS-based HER2 measurements strongly correlated with predicate assay HER2 determinations, and concordance was improved by normalizing to glyceraldehyde-3-phosphate dehydrogenase. HER2 was quantified above the LLOQ in all tumors. CONCLUSIONS: Immuno-MRM-MS can be used to quantify HER2 in FFPE and frozen BC biopsies, even at low HER2 expression levels.

NCCN Guidelines® Insights: Breast Cancer, Version 4.2021.

The NCCN Guidelines for Breast Cancer include up-to-date guidelines for clinical management of patients with carcinoma in situ, invasive breast cancer, Paget disease, phyllodes tumor, inflammatory breast cancer, male breast cancer, and breast cancer during pregnancy. These guidelines are developed by a multidisciplinary panel of representatives from NCCN Member Institutions with breast cancer-focused expertise in the fields of medical oncology, surgical oncology, radiation oncology, pathology, reconstructive surgery, and patient advocacy. These NCCN Guidelines Insights focus on the most recent updates to recommendations for adjuvant systemic therapy in patients with nonmetastatic, early-stage, hormone receptor-positive, HER2-negative breast cancer.

The path to a better biomarker: application of a risk management framework for the implementation of PD-L1 and TILs as immuno-oncology biomarkers in breast cancer clinical trials and daily practice.

Immune checkpoint inhibitor therapies targeting PD-1/PD-L1 are now the standard of care in oncology across several hematologic and solid tumor types, including triple negative breast cancer (TNBC). Patients with metastatic or locally advanced TNBC with PD-L1 expression on immune cells occupying ≥1% of tumor area demonstrated survival benefit with the addition of atezolizumab to nab-paclitaxel. However, concerns regarding variability between immunohistochemical PD-L1 assay performance and inter-reader reproducibility have been raised. High tumor-infiltrating lymphocytes (TILs) have also been associated with response to PD-1/PD-L1 inhibitors in patients with breast cancer (BC). TILs can be easily assessed on hematoxylin and eosin-stained slides and have shown reliable inter-reader reproducibility. As an established prognostic factor in early stage TNBC, TILs are soon anticipated to be reported in daily practice in many pathology laboratories worldwide. Because TILs and PD-L1 are parts of an immunological spectrum in BC, we propose the systematic implementation of combined PD-L1 and TIL analyses as a more comprehensive immuno-oncological biomarker for patient selection for PD-1/PD-L1 inhibition-based therapy in patients with BC. Although practical and regulatory considerations differ by jurisdiction, the pathology community has the responsibility to patients to implement assays that lead to optimal patient selection. We propose herewith a risk-management framework that may help mitigate the risks of suboptimal patient selection for immuno-therapeutic approaches in clinical trials and daily practice based on combined TILs/PD-L1 assessment in BC. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Integrated genomic characterization of ERBB2/HER2 alterations in invasive breast carcinoma: a focus on unusual FISH groups.

In patients with invasive breast cancer, fluorescence in situ hybridization (FISH) testing for HER2 typically demonstrates the clear presence or lack of ERBB2 (HER2) amplification (i.e., groups 1 or 5). However, a small subset of patients can present with unusual HER2 FISH patterns (groups 2-4), resulting in diagnostic confusion. To provide clarity, the 2018 CAP/ASCO HER2 testing guideline recommends additional testing using HER2 immunohistochemistry (IHC) for determining the final HER2 status. Despite this effort, the genomic correlates of unusual HER2 FISH groups remain poorly understood. Here, we used droplet digital PCR (ddPCR) and targeted next-generation sequencing (NGS) to characterize the genomic features of both usual and unusual HER2 FISH groups. In this study, 51 clinical samples were selected to represent FISH groups 1-5. Furthermore, group 1 was subdivided into two groups, with groups 1A and 1B corresponding to cases with HER2 signals/cell ≥6.0 and 4-6, respectively. Overall, our findings revealed a wide range of copy number alterations in HER2 across the different FISH groups. As expected, groups 1A and 5 showed the clear presence and lack of HER2 copy number gain, respectively, as measured by ddPCR and NGS. In contrast, group 1B and other uncommon FISH groups (groups 2-4) were characterized by a broader range of HER2 copy levels with only a few select cases showing high-level gain. Notably, these cases with increased HER2 copy levels also showed HER2 overexpression by IHC, thus highlighting the correlation between HER2 copy number and HER2 protein expression. Given the concordance between the genomic and protein results, our findings suggest that HER2 IHC may inform HER2 copy number status in patients with unusual FISH patterns. Hence, our results support the current recommendation for using IHC to resolve HER2 status in FISH groups 2-4.

Primary mammary angiosarcomas harbor frequent mutations in KDR and PIK3CA and show evidence of distinct pathogenesis.

Angiosarcoma (AS) is the most frequent primary sarcoma of the breast but nevertheless remains uncommon, accounting for <0.05% of breast malignancies. Secondary mammary AS arise following radiation therapy for breast cancer, in contrast to primary AS which occur sporadically. Essentially all show aggressive clinical behavior independent of histologic grade and most are treated by mastectomy. MYC amplification is frequently identified in radiation-induced AS but only rarely in primary mammary AS (PMAS). As a heterogeneous group, AS from various anatomic sites have been shown to harbor recurrent alterations in TP53, MAP kinase pathway genes, and genes involved in angiogenic signaling including KDR (VEGFR2) and PTPRB. In part due to its rarity, the pathogenesis of PMAS has not been fully characterized. In this study, we examined the clinical, pathologic, and genomic features of ten cases of PMAS, including one patient with bilateral disease. Recurrent genomic alterations were identified in KDR (70%), PIK3CA/PIK3R1 (70%), and PTPRB (30%), each at higher frequencies than reported in AS across all sites. Six tumors harbored a KDR p.T771R hotspot mutation, and all seven KDR-mutant cases showed evidence suggestive of biallelism (four with loss of heterozygosity and three with two aberrations). Of the seven tumors with PI3K alterations, six harbored pathogenic mutations other than in the canonical PIK3CA residues which are most frequent in breast cancer. Three AS were hypermutated (≥10 mutations/megabase (Mb)); hypermutation was seen concurrent with KDR or PIK3CA mutations. The patient with bilateral disease demonstrated shared alterations, indicative of contralateral metastasis. No MYC or TP53 aberrations were detected in this series. Immunohistochemistry for VEGFR2 was unable to discriminate between KDR-mutant tumors and benign vascular lesions of the breast. These findings highlight the underrecognized frequency of KDR and PIK3CA mutation in PMAS, and a significant subset with hypermutation, suggesting a pathogenesis distinct from other AS.

Breast Cancer, Version 3.2020, NCCN Clinical Practice Guidelines in Oncology.

Several new systemic therapy options have become available for patients with metastatic breast cancer, which have led to improvements in survival. In addition to patient and clinical factors, the treatment selection primarily depends on the tumor biology (hormone-receptor status and HER2-status). The NCCN Guidelines specific to the workup and treatment of patients with recurrent/stage IV breast cancer are discussed in this article.

Pretreatment Tattoo Marking of Suspicious Axillary Lymph Nodes: Reliability and Correlation with Sentinel Lymph Node.

BACKGROUND: Tattooing is an alternative method for marking biopsied axillary lymph nodes (ALNs) before initiation of treatments for newly diagnosed breast cancer. Detection of black ink-stained nodes is performed under direct visualization at surgery and is combined with sentinel node (SLN) mapping procedures. METHODS: Women with newly diagnosed breast cancer who underwent fine or core-needle biopsy of suspicious ALNs were recruited. The nodal cortex and perinodal soft tissue was injected with 0.1-1.0 ml of Spot™ (GI Supply) black ink under ultrasound guidance. Intraoperatively, black stained nodes were removed along with SLNs, noting concordance between the two. RESULTS: Sixty-six evaluable patients were enrolled (2013-2017). Nineteen received surgery first (Group 1) and 47 neoadjuvant therapy (NAT, Group 2). The average number of nodes tattooed was 1.16 for Group 1 and 1.04 for Group 2. The average interval from tattoo to surgery was 21 days (range 1-62) for Group 1 and 148 days (range 71-257) for Group 2. The tattooed node(s) were visually identified at surgery and corresponded to the sentinel lymph node(s) in 98.5% of cases (18/19 in Group 1 and 47/47 in Group 2). Of the 14 patients in Group 2 whose nodes remained positive following NAT, the tattooed node was the SLN associated with carcinoma. CONCLUSIONS: Tattooing is an alternative method for marking biopsied ALNs. Tattooed nodes coincided with SLNs in 98.5% of cases. This technique is advantageous, because it allows for fewer procedures and lower costs compared with other methods.

NCCN Guidelines Insights: Breast Cancer, Version 3.2018.

These NCCN Guidelines Insights highlight the updated recommendations for use of multigene assays to guide decisions on adjuvant systemic chemotherapy therapy for women with hormone receptor-positive, HER2-negative early-stage invasive breast cancer. This report summarizes these updates and discusses the rationale behind them.

Second opinion strategies in breast pathology: a decision analysis addressing over-treatment, under-treatment, and care costs.

PURPOSE: To estimate the potential near-term population impact of alternative second opinion breast biopsy pathology interpretation strategies. METHODS: Decision analysis examining 12-month outcomes of breast biopsy for nine breast pathology interpretation strategies in the U.S. health system. Diagnoses of 115 practicing pathologists in the Breast Pathology Study were compared to reference-standard-consensus diagnoses with and without second opinions. Interpretation strategies were defined by whether a second opinion was sought universally or selectively (e.g., 2nd opinion if invasive). Main outcomes were the expected proportion of concordant breast biopsy diagnoses, the proportion involving over- or under-interpretation, and cost of care in U.S. dollars within one-year of biopsy. RESULTS: Without a second opinion, 92.2% of biopsies received a concordant diagnosis. Concordance rates increased under all second opinion strategies, and the rate was highest (95.1%) and under-treatment lowest (2.6%) when all biopsies had second opinions. However, over-treatment was lowest when second opinions were sought selectively for initial diagnoses of invasive cancer, DCIS, or atypia (1.8 vs. 4.7% with no 2nd opinions). This strategy also had the lowest projected 12-month care costs ($5.907 billion vs. $6.049 billion with no 2nd opinions). CONCLUSIONS: Second opinion strategies could lower overall care costs while reducing both over- and under-treatment. The most accurate cost-saving strategy required second opinions for initial diagnoses of invasive cancer, DCIS, or atypia.

Will oncotype DX DCIS testing guide therapy? A single-institution correlation of oncotype DX DCIS results with histopathologic findings and clinical management decisions.

Given the increased detection rates of ductal carcinoma in situ (DCIS) and the limited overall survival benefit from adjuvant breast irradiation after breast-conserving surgery, there is interest in identifying subsets of patients who have low rates of ipsilateral breast tumor recurrence such that they might safely forgo radiation. The Oncotype DCIS score is a reverse transcription-PCR (RT-PCR)-based assay that was validated to predict which DCIS cases are most likely to recur. Clinically, these results may be used to assist in selecting which patients with DCIS might safely forgo radiation therapy after breast-conserving surgery; however, little is currently published on how this test is being used in practice. Our study examines traditional histopathologic features used in predicting DCIS risk with Oncotype DCIS results and how these results affect clinical decision-making at our academic institution. Histopathologic features and management decisions for 37 cases with Oncotype DCIS results over the past 4 years were collected. Necrosis, high nuclear grade, biopsy site change, estrogen receptor and progesterone receptor positivity <90% on immunohistochemistry, and Van Nuys Prognostic Index score of 8 or greater were significant predictors of an intermediate-high recurrence score on multivariate regression analysis (P<0.02). Low Oncotype DCIS scores and low nuclear grade were associated with lower rate of radiation therapy (P<0.008). There were seven cases (19%) with Oncotype DCIS results that we considered unexpected in relation to the histopathologic findings (ie, high nuclear grade with comedonecrosis and a low Oncotype score, or hormone receptor discrepancies). Overall, pathologic features correlate with Oncotype DCIS scores but unexpected results do occur, making individual recommendations sometimes challenging.

The molecular basis of breast cancer pathological phenotypes.

The histopathological evaluation of morphological features in breast tumours provides prognostic information to guide therapy. Adjunct molecular analyses provide further diagnostic, prognostic and predictive information. However, there is limited knowledge of the molecular basis of morphological phenotypes in invasive breast cancer. This study integrated genomic, transcriptomic and protein data to provide a comprehensive molecular profiling of morphological features in breast cancer. Fifteen pathologists assessed 850 invasive breast cancer cases from The Cancer Genome Atlas (TCGA). Morphological features were significantly associated with genomic alteration, DNA methylation subtype, PAM50 and microRNA subtypes, proliferation scores, gene expression and/or reverse-phase protein assay subtype. Marked nuclear pleomorphism, necrosis, inflammation and a high mitotic count were associated with the basal-like subtype, and had a similar molecular basis. Omics-based signatures were constructed to predict morphological features. The association of morphology transcriptome signatures with overall survival in oestrogen receptor (ER)-positive and ER-negative breast cancer was first assessed by use of the Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) dataset; signatures that remained prognostic in the METABRIC multivariate analysis were further evaluated in five additional datasets. The transcriptomic signature of poorly differentiated epithelial tubules was prognostic in ER-positive breast cancer. No signature was prognostic in ER-negative breast cancer. This study provided new insights into the molecular basis of breast cancer morphological phenotypes. The integration of morphological with molecular data has the potential to refine breast cancer classification, predict response to therapy, enhance our understanding of breast cancer biology, and improve clinical management. This work is publicly accessible at www.dx.ai/tcga_breast. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Characteristics and clinical outcomes of pleomorphic lobular carcinoma in situ of the breast.

Pleomorphic lobular carcinoma in situ (PLCIS) of the breast is a rare variant of lobular carcinoma in situ (LCIS). We reviewed 78 cases of PLCIS diagnosed at our institution from 1998 to 2012. Among all cases, 47 (60%) were associated with invasive carcinoma and/or ductal carcinoma in situ (DCIS) after final surgical excision. Of the 20 cases with PLCIS alone on core needle biopsy (CNB), 6 (30%) were upgraded to invasive carcinoma or DCIS after final surgical excision. Our findings support a recommendation for complete surgical excision of PLCIS when diagnosed on CNB.

'Non-classical' HER2 FISH results in breast cancer: a multi-institutional study.

The 2013 CAP/ASCO HER2 Testing Guidelines Update modified HER2 FISH categories such that some cases with 'monosomy', 'co-amplification/polysomy', low-level increased HER2 signals or clustered heterogeneity now are considered amplified or equivocal. This study examines the frequency and clinico-pathologic characteristics of breast cancers with equivocal or 'non-classical' HER2 FISH results. Breast cancers (2001-2014) with HER2 FISH results, HER2 immunohistochemistry, ER, grade, and age from three institutions (Stanford, UCSF, UWMC) were collected. HER2 FISH was interpreted using the updated recommendations. Amplified cases with non-classical results were grouped into the following categories: (1) 'monosomy' (ratio ≥2.0, mean HER2/cell<4.0); (2) 'co-amplified' (ratio<2.0, mean HER2/cell ≥6.0); (3) 'low amplified' (ratio ≥2.0, mean HER2/cell 4.0-5.9). Heterogeneous cases with clustered HER2-positive cells were also included. Of 8068 cases, 5.2% were equivocal and 4.6% had a 'non-classical' HER2 amplified result; 1.4% 'monosomy', 0.8% 'co-amplified', 2.1% 'low amplified', and 0.3% clustered heterogeneity. These cancers had a high frequency of ER positive (80.4%), Nottingham grade 3 (52.1%) results. The highest percentage of grade 3 cancers (66.7%) and positive HER2 immunohistochemistry (31.7%) was in the 'co-amplified' group. The 'monosomy' group had the highest percent grade 1 cancers (13.3%) and was most frequently HER2 immunohistochemistry negative (30.1%). Equivocal cases had very similar characteristics to the 'low-amplified' category. Cases with non-classical HER2 amplification or equivocal results are typically ER positive, higher grade cancers. 'Co-amplified' cases have the highest frequencies of aggressive characteristics and 'monosomy' cases the highest frequencies of lower risk features. With little clinical outcomes data currently available on these non-classical HER2 results, these results support the current classification scheme for HER2 FISH, with case-by-case correlation with additional clinical-pathologic factors when evaluating whether to offer HER2-targeted therapies in these non-classical cases.