Breast Hemangiomas: Imaging Features With Histopathology Correlation.

Breast hemangiomas are rare benign vascular lesions. In a previously performed review of approximately 10,000 breast surgical pathology results, roughly 0.15% (15/~10,000) were hemangiomas. Hemangiomas are more frequent in women and have a documented age distribution of 1.5 to 82 years. They are most often subcutaneous or subdermal and anterior to the anterior mammary fascia but may rarely be seen in the pectoralis muscles or chest wall. On imaging, breast hemangiomas typically present as oval or round masses, often measuring less than 2.5 cm, with circumscribed or mostly circumscribed, focally microlobulated margins, equal or high density on mammography, and variable echogenicity on US. Calcifications, including phleboliths, can be seen. Color Doppler US often shows hypovascularity or avascularity. MRI appearance can vary, although hemangiomas are generally T2 hyperintense and T1 hypointense with variable enhancement. Pathologic findings vary by subtype, which include perilobular, capillary, cavernous, and venous hemangiomas. If core biopsy pathology results are benign, without atypia, and concordant with imaging and clinical findings, surgical excision is not routinely indicated. Because of histopathologic overlap with well-differentiated or low-grade angiosarcomas, surgical excision may be necessary for definitive diagnosis. Findings that are more common with angiosarcomas include size greater than 2 cm, hypervascularity on Doppler US, irregular shape, and invasive growth pattern.

Radiation-Induced Morphea of the Breast Treated With Wide Local Excision and Abdominal Free Flap Breast Reconstruction.

Radiation-induced morphea (RIM) associated with breast cancer treatment is a rare and underdiagnosed skin complication of radiotherapy that can lead to severe and painful contractures, resulting in disfigurement, failure of reconstruction, and poor quality of life in patients. The condition may present on a spectrum of local or more generalized forms involving skin over the breast and anterior chest wall. This diagnosis must be differentiated from post-radiation fibrosis, infection, cancer recurrence, inflammatory breast cancer, and other inflammatory conditions as the clinical course and treatment approaches differ. Various noninvasive and topical agents have been used; however, many cases are refractory to treatment. Surgery has been less commonly described in the management of generalized RIM. This report describes a case of RIM in a patient with breast cancer who experienced simultaneous resolution of symptoms as well as successful breast reconstruction using autologous free-tissue transfer.

Wilms Tumor: An Unexpected Diagnosis in Adult Patients.

CONTEXT.­: Wilms tumor (WT) in adult patients is rare and has historically been a diagnostic and therapeutic conundrum, with limited data available in the literature. OBJECTIVE.­: To provide detailed diagnostic features, molecular profiling, and patient outcomes in a multi-institutional cohort of adult WT patients. DESIGN.­: We identified and retrospectively examined 4 adult WT cases. RESULTS.­: Two patients presented with metastatic disease, and diagnoses were made on fine-needle aspiration of their renal masses. The aspirates included malignant primitive-appearing epithelioid cells forming tubular rosettes and necrosis, and cell blocks demonstrated triphasic histology. In the remaining 2 cases, patients presented with localized disease and received a diagnosis on resection, with both patients demonstrating an epithelial-predominant morphology. Tumor cells in all cases were patchy variable positive for PAX8 and WT1 immunohistochemistry. Next-generation sequencing identified alterations previously reported in pediatric WT in 3 of 4 cases, including mutations in ASXL1 (2 of 4), WT1 (1 of 4), and the TERT promoter (1 of 4), as well as 1q gains (1 of 4); 1 case showed no alterations. Three patients were treated with pediatric chemotherapy protocols; during follow up (range, 26-60 months), 1 patient died of disease. CONCLUSIONS.­: WT is an unexpected and difficult entity to diagnose in adults and should be considered when faced with a primitive-appearing renal or metastatic tumor. Molecular testing may help exclude other possibilities but may not be sensitive or specific because of the relatively large number of driver mutations reported in WT.

Solid-Basaloid Adenoid Cystic Carcinoma of the Breast: An Aggressive Subtype Enriched for Notch Pathway and Chromatin Modifier Mutations With MYB Overexpression.

Adenoid cystic carcinoma (AdCC) is a rare triple-negative breast cancer analogous to its extramammary counterparts. Diagnosis of the more aggressive solid-basaloid variant of AdCC (SB-AdCC) can be challenging due to poorly defined histopathologic and molecular features. We characterized 22 invasive and in situ basaloid carcinomas by morphology, immunohistochemistry, genetics, and MYB status using multiple platforms and assessed clinical behavior and neoadjuvant chemotherapy responses. After consensus review, 16/22 cases were classified as SB-AdCC. All SB-AdCC had predominantly solid growth and at least focal myxohyaline stroma and were immune-poor. Eosinophilic squamoid cells (69%, 11/16) and basement membrane-like secretions (69%, 11/16) were common, and intercalated ducts (31%, 5/16) were less frequent. SB-AdCC typically expressed SOX10 (100%, 16/16) and luminal markers (100%, 16/16 CK7; 88%, 14/16 CD117; 93%, 13/14 CAM5.2). SMA (40%, 6/15) expression was less common, and SMM (27%, 3/11), GATA3 (20%, 3/15), and p63 (25%, 4/16) were mostly negative. MYB protein and/or MYB RNA overexpression was universal in evaluable cases (13/13), with RNA in situ hybridization (10/10) more reliable than immunohistochemistry (10/11, plus 4 excisions inconclusive). Fluorescence in situ hybridization and/or next-generation sequencing identified MYB rearrangements (20%, 3/15) and amplifications/copy gains (60%, 9/15) but no MYB::NFIB fusions. SB-AdCC often had aberrations in Notch pathway (60%, including 40% NOTCH1 and 20% NOTCH2) and/or chromatin modifier (60%, including 33% CREBBP) genes, with relatively infrequent TP53 mutations (27%). Unclassified invasive basaloid carcinomas lacking described histologic features of SB-AdCC (n = 4) and basaloid ductal carcinoma in situ (n = 2) showed similar immunoprofiles and genetics as SB-AdCC, including Notch aberrations and MYB overexpression with MYB rearrangements/amplifications. Overall, nodal (22%) and distant (33%) metastases were common, and 23% of patients died of disease (mean follow-up, 35 months; n = 22). Responses were poor in all 7 neoadjuvant chemotherapy-treated patients, without any achieving pathologic complete response. The data highlight the histopathologic spectrum of basaloid carcinomas including SB-AdCC and reveal shared genetics and MYB activation, which can be diagnostically useful. Aggressive behavior and poor treatment responses emphasize a need for additional treatment approaches.

Low-grade fibromyxoid sarcoma of the breast: genetic characterization and immunohistochemical comparison to morphologic mimics.

Spindle cell lesions of the breast elicit a specific, relatively limited differential diagnosis, and accurate classification often requires careful morphologic evaluation and immunohistochemical workup. Low-grade fibromyxoid sarcoma (LGFMS) is a rare malignant fibroblastic tumor with deceptively bland spindle cell morphology. Involvement of the breast is exceedingly rare. We examined the clinicopathologic and molecular characteristics of three cases of breast/axillary LGFMS. In addition, we interrogated the immunohistochemical expression of MUC4, a commonly used marker of LGFMS, in other breast spindle cell lesions. LGFMS presented in women at 23, 33, and 59 years of age. Tumor size ranged from 0.9 to 4.7 cm. Microscopically, they were circumscribed nodular masses composed of bland spindle cells with fibromyxoid stroma. Immunohistochemically, tumors were diffusely positive for MUC4 and negative for keratin, CD34, S100 protein, and nuclear beta-catenin. Fluorescence in-situ hybridization demonstrated FUS (n = 2) or EWSR1 (n = 1) rearrangements. Next-generation sequencing identified FUS::CREB3L2 and EWSR1::CREB3L1 fusions. MUC4 immunohistochemistry performed on 162 additional breast lesions demonstrated only weak and limited expression in a subset of cases of fibromatosis (10/20, ≤30% staining), scar (5/9, ≤10%), metaplastic carcinoma (4/23, ≤5%), and phyllodes tumor (3/74, ≤10%). MUC4 was entirely negative in cases of pseudoangiomatous stromal hyperplasia (n = 9), myofibroblastoma (n = 6), periductal stromal tumor (n = 3), and cellular/juvenile fibroadenoma (n = 21). LGFMS can rarely occur in the breast and should be considered in the differential diagnosis of breast spindle cell lesions. Strong and diffuse MUC4 expression is highly specific in this histologic context. Detection of an FUS or EWSR1 rearrangement can confirm the diagnosis.

Genetic and Immunohistochemical Profiling of Mammary Hidradenoma and Comparison to Mucoepidermoid Carcinoma.

Mucoepidermoid carcinoma (MEC) is exceedingly rare in the breast, with <45 cases reported in the literature. Although estrogen receptor/progesterone receptor/human epidermal growth factor 2 triple-negative, MEC is characterized as a special subtype of breast carcinoma with significantly better prognosis than conventional basal-type tumors. Cutaneous hidradenoma (HA) is considered a benign adnexal neoplasm showing histomorphologic overlap with MEC. Rare cases of HA have also been reported in the breast, but these are relatively uncharacterized. In this study, we examined the clinicopathologic, immunohistochemical (IHC), and genetic features of 8 breast HAs, in comparison to 3 mammary MECs. All cases were positive for MAML2 break-apart fluorescence in situ hybridization. Eight cases demonstrated a CRTC1::MAML2 fusion, and one MEC harbored a CRTC3::MAML2 fusion; the latter is a novel finding in the breast. Mutational burden was very low, with only one HA exhibiting a MAP3K1 pathogenic alteration. By IHC, both MEC and HA demonstrated cell type-dependent expression of high- and low-molecular-weight keratins and p63, as well as negative to low-positive estrogen receptor and androgen receptor. Smooth muscle myosin and calponin highlighted an in situ component in the 3 cases of MEC; expression of these myoepithelial markers was negative in HAs. Additional distinguishing characteristics included the growth pattern and tumor architecture, the presence of glandular/luminal cells in HA, and overall higher IHC expression of SOX10, S100 protein, MUC4, and mammaglobin in MEC. Morphologic findings were also compared to a series of 27 cutaneous nonmammary HAs. Mucinous and glandular/luminal cells were identified in significantly more mammary HAs than nonmammary lesions. The findings provide insight into the pathogenesis of MAML2-rearranged neoplasms of the breast, underscore the overlapping genetic features of MEC and HA, and highlight similarities to their extramammary counterparts.

Contemporary diagnostic approach to atypical vascular lesion and angiosarcoma.

Vascular neoplasms account for a substantial fraction of cutaneous mesenchymal tumors, spanning from clinically indolent benign lesions to highly aggressive malignancies. These neoplasms present a distinctive challenge in terms of their diagnostic histopathology, both because of the breadth of their morphological manifestations and because of the significant histological overlap between different entities, even benign and malignant ones. The post-radiotherapy setting is particularly problematic diagnostically, insofar as radiation exposure predisposes not only to secondary angiosarcoma, but also to atypical vascular lesion, a largely benign proliferation of cutaneous blood vessels typically affecting the breast. To address these challenges, we explore the clinical, histological, and molecular features of malignant vascular neoplasia, including primary and secondary subtypes, through the comparative lens of atypical vascular lesion. In addition to highlighting the key morphological indicators of malignancy in superficial vasoformative tumors, we offer an approach that integrates clinical characteristics and molecular genetic profiling to facilitate accurate classification. With this current knowledge as our foundation, we also look ahead in an effort to frame some of the key unanswered questions regarding superficial vascular malignancies and their natural history, clinical management, and molecular underpinnings.

Triple-Negative Apocrine Carcinomas: Toward a Unified Group With Shared Molecular Features and Clinical Behavior.

Triple-negative apocrine carcinomas (TNACs) are rare breast tumors with limited studies evaluating their molecular characteristics and clinical behavior. We performed a histologic, immunohistochemical, genetic, and clinicopathologic assessment of 42 invasive TNACs (1 with a focal spindle cell component) from 41 patients, 2 pure apocrine ductal carcinomas in situ (A-DCIS), and 1 A-DCIS associated with spindle cell metaplastic carcinoma (SCMBC). All TNACs had characteristic apocrine morphology and expressed androgen receptor (42/42), gross cystic disease fluid protein 15 (24/24), and CK5/6 (16/16). GATA3 was positive in most cases (16/18, 89%), and SOX10 was negative (0/22). TRPS1 was weakly expressed in a minority of tumors (3/14, 21%). Most TNACs had low Ki67 proliferation (≤10% in 67%, 26/39), with a median index of 10%. Levels of tumor infiltrating lymphocytes were low (≤10% in 93%, 39/42, and 15% in 7%, 3/42). Eighteen percent of TNACs presented with axillary nodal metastasis (7/38). No patients treated with neoadjuvant chemotherapy achieved pathologic complete response (0%, 0/10). Nearly all patients with TNAC (97%, n = 32) were without evidence of disease at the time of study (mean follow-up of 62 months). Seventeen invasive TNACs and 10 A-DCIS (7 with paired invasive TNAC) were profiled by targeted capture-based next-generation DNA sequencing. Pathogenic mutations in phosphatidylinositol 3-kinase pathway genes PIK3CA (53%) and/or PIK3R1 (53%) were identified in all TNACs (100%), including 4 (24%) with comutated PTEN. Ras-MAPK pathway genes, including NF1 (24%), and TP53 were mutated in 6 tumors each (35%). All A-DCIS shared mutations, such as phosphatidylinositol 3-kinase aberrations and copy number alterations with paired invasive TNACs or SCMBC, and a subset of invasive carcinomas showed additional mutations in tumor suppressors (NF1, TP53, ARID2, and CDKN2A). Divergent genetic profiles between A-DCIS and invasive carcinoma were identified in 1 case. In summary, our findings support TNAC as a morphologically, immunohistochemically, and genetically homogeneous subgroup of triple-negative breast carcinomas and suggest overall favorable clinical behavior.

Uterine Inflammatory Myofibroblastic Tumors: Proposed Risk Stratification Model Using Integrated Clinicopathologic and Molecular Analysis.

Inflammatory myofibroblastic tumor (IMT) of the uterus is a rare mesenchymal tumor with largely benign behavior; however, a small subset demonstrate aggressive behavior. While clinicopathologic features have been previously associated with aggressive behavior, these reports are based on small series, and these features are imperfect predictors of clinical behavior. IMTs are most commonly driven by ALK fusions, with additional pathogenic molecular alterations being reported only in rare examples of extrauterine IMTs. In this study, a series of 11 uterine IMTs, 5 of which demonstrated aggressive behavior, were evaluated for clinicopathologic variables and additionally subjected to capture-based next-generation sequencing with or without whole-transcriptome RNA sequencing. In the 6 IMTs without aggressive behavior, ALK fusions were the sole pathogenic alteration. In contrast, all 5 aggressive IMTs harbored pathogenic molecular alterations and numerous copy number changes in addition to ALK fusions, with the majority of the additional alterations present in the primary tumors. We combined our series with cases previously reported in the literature and performed statistical analyses to propose a novel clinicopathologic risk stratification score assigning 1 point each for: age above 45 years, size≥5 cm,≥4 mitotic figures per 10 high-power field, and infiltrative borders. No tumors with 0 points had an aggressive outcome, while 21% of tumors with 1 to 2 points and all tumors with ≥3 points had aggressive outcomes. We propose a 2-step classification model that first uses the clinicopathologic risk stratification score to identify low-risk and high-risk tumors, and recommend molecular testing to further classify intermediate-risk tumors.

Transcriptional and Immune Landscape of Cardiac Sarcoidosis.

BACKGROUND: Cardiac involvement is an important determinant of mortality among sarcoidosis patients. Although granulomatous inflammation is a hallmark finding in cardiac sarcoidosis, the precise immune cell populations that comprise the granuloma remain unresolved. Furthermore, it is unclear how the cellular and transcriptomic landscape of cardiac sarcoidosis differs from other inflammatory heart diseases. METHODS: We leveraged spatial transcriptomics (GeoMx digital spatial profiler) and single-nucleus RNA sequencing to elucidate the cellular and transcriptional landscape of cardiac sarcoidosis. Using GeoMX digital spatial profiler technology, we compared the transcriptomal profile of CD68+ rich immune cell infiltrates in human cardiac sarcoidosis, giant cell myocarditis, and lymphocytic myocarditis. We performed single-nucleus RNA sequencing of human cardiac sarcoidosis to identify immune cell types and examined their transcriptomic landscape and regulation. Using multichannel immunofluorescence staining, we validated immune cell populations identified by single-nucleus RNA sequencing, determined their spatial relationship, and devised an immunostaining approach to distinguish cardiac sarcoidosis from other inflammatory heart diseases. RESULTS: Despite overlapping histological features, spatial transcriptomics identified transcriptional signatures and associated pathways that robustly differentiated cardiac sarcoidosis from giant cell myocarditis and lymphocytic myocarditis. Single-nucleus RNA sequencing revealed the presence of diverse populations of myeloid cells in cardiac sarcoidosis with distinct molecular features. We identified GPNMB (transmembrane glycoprotein NMB) as a novel marker of multinucleated giant cells and predicted that the MITF (microphthalmia-associated transcription factor) family of transcription factors regulated this cell type. We also detected additional macrophage populations in cardiac sarcoidosis including HLA-DR (human leukocyte antigen-DR)+ macrophages, SYTL3 (synaptotagmin-like protein 3)+ macrophages and CD163+ resident macrophages. HLA-DR+ macrophages were found immediately adjacent to GPMMB+ giant cells, a distinct feature compared with other inflammatory cardiac diseases. SYTL3+ macrophages were located scattered throughout the granuloma and CD163+ macrophages, CD1c+ dendritic cells, nonclassical monocytes, and T cells were located at the periphery and outside of the granuloma. Finally, we demonstrate mTOR (mammalian target of rapamycin) pathway activation is associated with proliferation and is selectively found in HLA-DR+ and SYLT3+ macrophages. CONCLUSIONS: In this study, we identified diverse populations of immune cells with distinct molecular signatures that comprise the sarcoid granuloma. These findings provide new insights into the pathology of cardiac sarcoidosis and highlight opportunities to improve diagnostic testing.

The Interaction of SWI/SNF with the Ribosome Regulates Translation and Confers Sensitivity to Translation Pathway Inhibitors in Cancers with Complex Perturbations.

Subunits from the chromatin remodelers mammalian SWItch/Sucrose Non-Fermentable (mSWI/SNF) are mutated, deleted, or amplified in more than 40% of cancers. Understanding their functions in normal cells and the consequences of cancerous alterations will provide insight into developing new targeted therapies. Here we examined whether mSWI/SNF mutations increase cellular sensitivity to specific drugs. Taking advantage of the DepMap studies, we demonstrate that cancer cells harboring mutations of specific mSWI/SNF subunits exhibit a genetic dependency on translation factors and are sensitive to translation pathway inhibitors. Furthermore, mSWI/SNF subunits were present in the cytoplasm and interacted with the translation initiation machinery, and short-term inhibition and depletion of specific subunits decreased global translation, implicating a direct role for these factors in translation. Depletion of specific mSWI/SNF subunits also increased sensitivity to mTOR-PI3K inhibitors. In patient-derived breast cancer samples, mSWI/SNF subunits expression in both the nucleus and the cytoplasm was substantially altered. In conclusion, an unexpected cytoplasmic role for mSWI/SNF complexes in translation suggests potential new therapeutic opportunities for patients afflicted by cancers demonstrating alterations in their subunits. SIGNIFICANCE: This work establishes direct functions for mSWI/SNF in translation and demonstrates that alterations in mSWI/SNF confer a therapeutic vulnerability to translation pathway inhibitors in cancer cells.

Genetic and immunohistochemical profiling of small cell and large cell neuroendocrine carcinomas of the breast.

Neuroendocrine carcinomas (NEC) of the breast are exceedingly rare tumors, which are classified in the WHO system as small cell (SCNEC) and large cell (LCNEC) carcinoma based on indistinguishable features from their lung counterparts. In contrast to lung and enteropancreatic NEC, the genomics of breast NEC have not been well-characterized. In this study, we examined the clinicopathologic, immunohistochemical, and genetic features of 13 breast NEC (7 SCNEC, 4 LCNEC, 2 NEC with ambiguous small versus large cell morphology [ANEC]). Co-alterations of TP53 and RB1 were identified in 86% (6/7) SCNEC, 100% (2/2) ANEC, and 50% (2/4) LCNEC. The one SCNEC without TP53/RB1 alteration had other p53 pathway aberrations (MDM2 and MDM4 amplification) and was immunohistochemically RB negative. PIK3CA/PTEN pathway alterations and ZNF703 amplifications were each identified in 46% (6/13) NEC. Two tumors (1 SCNEC, 1 LCNEC) were CDH1 mutated. By immunohistochemistry, 100% SCNEC (6/6) and ANEC (2/2) and 50% (2/4) LCNEC (83% NEC) showed RB loss, compared to 0% (0/8) grade 3 neuroendocrine tumors (NET) (p < 0.001) and 38% (36/95) grade 3 invasive ductal carcinomas of no special type (IDC-NST) (p = 0.004). NEC were also more often p53 aberrant (60% vs 0%, p = 0.013), ER negative (69% vs 0%, p = 0.005), and GATA3 negative (67% vs 0%, p = 0.013) than grade 3 NET. Two mixed NEC had IDC-NST components, and 69% (9/13) of tumors were associated with carcinoma in situ (6 neuroendocrine DCIS, 2 non-neuroendocrine DCIS, 1 non-neuroendocrine LCIS). NEC and IDC-NST components of mixed tumors were clonally related and immunophenotypically distinct, lacking ER and GATA3 expression in NEC relative to IDC-NST, with RB loss only in NEC of one ANEC. The findings provide insight into the pathogenesis of breast NEC, underscore their classification as a distinct tumor type, and highlight genetic similarities to extramammary NEC, including highly prevalent p53/RB pathway aberrations in SCNEC.

Spatial proteomic characterization of HER2-positive breast tumors through neoadjuvant therapy predicts response.

The addition of HER2-targeted agents to neoadjuvant chemotherapy has dramatically improved pathological complete response (pCR) rates in early-stage, HER2-positive breast cancer. Nonetheless, up to 50% of patients have residual disease after treatment, while others are likely overtreated. Here, we performed multiplex spatial proteomic characterization of 122 samples from 57 HER2-positive breast tumors from the neoadjuvant TRIO-US B07 clinical trial sampled pre-treatment, after 14-21 d of HER2-targeted therapy and at surgery. We demonstrated that proteomic changes after a single cycle of HER2-targeted therapy aids the identification of tumors that ultimately undergo pCR, outperforming pre-treatment measures or transcriptomic changes. We further developed and validated a classifier that robustly predicted pCR using a single marker, CD45, measured on treatment, and showed that CD45-positive cell counts measured via conventional immunohistochemistry perform comparably. These results demonstrate robust biomarkers that can be used to enable the stratification of sensitive tumors early during neoadjuvant HER2-targeted therapy, with implications for tailoring subsequent therapy.

Molecular Testing in Breast Cancer: Current Status and Future Directions.

Molecular testing in breast cancer is a rapidly developing field that is becoming increasingly integral to patient care. This article provides an overview of currently available molecular assays and testing modalities that have prognostic, predictive, and therapeutic value. These include multigene assays for invasive breast cancer (Oncotype DX, MammaPrint, Prosigna, and Breast Cancer Index) and ductal carcinoma in situ (Oncotype DX DCIS and DCISionRT) and companion tests to detect PIK3CA mutations and NTRK fusions. The various assays related to immune checkpoint inhibitors, consisting of immunohistochemistry with anti-programmed death-ligand 1 antibodies SP142 and 22C3 and detection of microsatellite instability, mismatch repair deficiency, and tumor mutational burden are also discussed. Finally, the practical utility and hopeful promise of next-generation sequencing panels and circulating tumor (cell-free) DNA assays are evaluated. This review should serve as a useful and practical reference for practicing pathologists, molecular pathologists, clinicians, and researchers.

Skin angiography assisted mastectomy in secondary breast angiosarcoma: Complete clinical response after neoadjuvant immunotherapy.

Radiation-induced breast angiosarcoma, or secondary angiosarcoma (SAS), is a rare entity with a high risk of metastatic recurrence. Herein, we describe the use of intraoperative fluorescence-based skin angiography to guide surgical resection following a novel immunotherapy-based regimen for SAS resulting in a complete pathological response.

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.

PDGFB RNA in situ hybridization for the diagnosis of dermatofibrosarcoma protuberans.

Dermatofibrosarcoma protuberans (DFSP) is a spindle cell neoplasm of the skin and superficial soft tissue with a tendency for locally aggressive behavior; metastatic potential coincides with fibrosarcomatous transformation. The vast majority of DFSPs harbor the t(17;22) translocation resulting in a COL1A1-PDGFB fusion that drives autocrine growth stimulation via PDGFB overexpression. Here, we examined the utility of PDGFB RNA chromogenic in situ hybridization (CISH) for the diagnosis of DFSP. A total of 337 tumors represented in whole tissue sections and tissue microarrays, including 37 cases of DFSP and 300 histologically similar spindle cell tumors, were subjected to PDGFB RNA CISH using commercially available probes. PDGFB overexpression was observed by light microscopy in 24 of 26 conventional DFSPs (92%) and 11 of 11 fibrosarcomatous DFSPs (100%). One of two DFSPs negative for PDGFB by RNA CISH was found to harbor an uncommon alternative rearrangement involving PDGFD. All examined cases of histologic mimics were negative for PDGFB overexpression; limited PDGFB expression, not reaching an empirical threshold of greater than 5 puncta or one aggregate of chromogen in more than 25% of cells, was observed in 7 of 300 mimics (2.3%), including desmoplastic melanoma, malignant peripheral nerve sheath tumor, angiosarcoma, and pleomorphic dermal sarcoma. Vascular PDGFB expression was seen in several tumor types. We conclude that PDGFB RNA CISH, with careful interpretation and the use of appropriate thresholds, may serve as a surrogate marker of PDGFB rearrangement and a useful ancillary tool for the diagnosis of DFSP.

Pathologic and molecular responses to neoadjuvant trastuzumab and/or lapatinib from a phase II randomized trial in HER2-positive breast cancer (TRIO-US B07).

In this multicenter, open-label, randomized phase II investigator-sponsored neoadjuvant trial with funding provided by Sanofi and GlaxoSmithKline (TRIO-US B07, Clinical Trials NCT00769470), participants with early-stage HER2-positive breast cancer (N = 128) were recruited from 13 United States oncology centers throughout the Translational Research in Oncology network. Participants were randomized to receive trastuzumab (T; N = 34), lapatinib (L; N = 36), or both (TL; N = 58) as HER2-targeted therapy, with each participant given one cycle of this designated anti-HER2 therapy alone followed by six cycles of standard combination chemotherapy with the same anti-HER2 therapy. The primary objective was to estimate the rate of pathologic complete response (pCR) at the time of surgery in each of the three arms. In the intent-to-treat population, we observed similar pCR rates between T (47%, 95% confidence interval [CI] 30-65%) and TL (52%, 95% CI 38-65%), and a lower pCR rate with L (25%, 95% CI 13-43%). In the T arm, 100% of participants completed all protocol-specified treatment prior to surgery, as compared to 69% in the L arm and 74% in the TL arm. Tumor or tumor bed tissue was collected whenever possible pre-treatment (N = 110), after one cycle of HER2-targeted therapy alone (N = 89), and at time of surgery (N = 59). Higher-level amplification of HER2 and hormone receptor (HR)-negative status were associated with a higher pCR rate. Large shifts in the tumor, immune, and stromal gene expression occurred after one cycle of HER2-targeted therapy. In contrast to pCR rates, the L-containing arms exhibited greater proliferation reduction than T at this timepoint. Immune expression signatures increased in all arms after one cycle of HER2-targeted therapy, decreasing again by the time of surgery. Our results inform approaches to early assessment of sensitivity to anti-HER2 therapy and shed light on the role of the immune microenvironment in response to HER2-targeted agents.

Evaluation of ductal carcinoma in situ grade via triple-modal molecular imaging of B7-H3 expression.

Ductal carcinoma in situ (DCIS) will account for 62,930 cases of breast cancer in 2019. DCIS is a pre-invasive lesion which may not progress to invasive carcinoma, yet surgery remains the mainstay treatment. Molecular imaging of a specific marker for DCIS grade for detection and active surveillance are critically needed to reduce potential overtreatment. First, breast cancer marker B7-H3 (CD276) expression was evaluated by immunohistochemical staining in 123 human specimens including benign epithelium (H-score 10.0 ± 8.2) and low (20.8 ± 17.7), intermediate (87.1 ± 69.5), and high (159.1 ± 87.6) grade DCIS, showing a positive association with DCIS nuclear grade (P < 0.001, AUC 0.96). Next, a murine DCIS model was combined with ultrasound molecular imaging of B7-H3 targeted microbubbles to differentiate normal glands from those harboring DCIS (n = 100, FVB/N-Tg(MMTVPyMT)634Mul, AUC 0.89). Finally, photoacoustic and fluorescence molecular imaging with an anti-B7-H3 antibody-indocyanine green conjugate were utilized for DCIS detection (n = 53). Molecular imaging of B7-H3 expression may allow for active surveillance of DCIS.