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.

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.

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.

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.

Pan-TRK Immunohistochemistry: A Useful Diagnostic Adjunct For Secretory Carcinoma of the Breast.

Secretory carcinoma is a special-type breast carcinoma underpinned by a recurrent t(12;15)(p13;q25) translocation resulting in ETV6-NTRK3 gene fusion. Immunohistochemistry (IHC) using a pan-TRK antibody has been recently shown to help identify NTRK rearrangements in other tumor types. The purpose of this study was to assess the diagnostic utility of pan-TRK IHC in secretory carcinoma of the breast. Pan-TRK IHC was performed using a rabbit monoclonal antibody on whole sections of 24 breast secretory carcinomas and tissue microarray sections of other breast carcinoma types (n=203) and histologic mimics (n=15). Cases were assessed for staining intensity and localization. The 24 patients with secretory carcinoma had a median age of 44 years and a median tumor size of 1.0 cm. ETV6 fluorescence in situ hybridization was positive in all cases tested (n=20). Twenty-three cases (95.8%) showed staining with pan-TRK, which was exclusively nuclear in 19, primarily nuclear with weak cytoplasmic staining in 3, and primarily cytoplasmic with focal nuclear staining in 1. The nuclear staining was diffuse in 17 and at least focally strong in 17. The only pan-TRK negative case was a core biopsy with limited tumor. Among the 203 nonsecretory carcinomas, 21 (10.3%) showed focal, weak nuclear staining in <5% of tumor cells and 1 (0.5%) showed focal membranous staining. All histologic mimics were negative. In conclusion, diffuse and/or at least focally strong nuclear pan-TRK staining is a sensitive and specific marker for secretory carcinoma of the breast.

Genomic profiling of breast secretory carcinomas reveals distinct genetics from other breast cancers and similarity to mammary analog secretory carcinomas.

Secretory carcinomas of the breast are rare tumors with distinct histologic features, recurrent t(12;15)(p13;q25) translocation resulting in ETV6-NTRK3 gene fusion and indolent clinical behavior. Mammary analog secretory carcinomas arising in other sites are histopathologically similar to the breast tumors and also harbor ETV6-NTRK3 fusions. Breast secretory carcinomas are often triple (estrogen and progesterone receptor, HER2) negative with a basal-like immunophenotype. However, genomic studies are lacking, and whether these tumors share genetic features with other basal and/or triple negative breast cancers is unknown. Aside from shared ETV6-NTRK3 fusions, the genetic relatedness of secretory carcinomas arising in different sites is also uncertain. We immunoprofiled and sequenced 510 cancer-related genes in nine breast secretory carcinomas and six salivary gland mammary analog secretory carcinomas. Immunoprofiles of breast and salivary gland secretory carcinomas were similar. All the tumors showed strong diffuse MUC4 expression (n=15), and SOX10 was positive in all nine breast and in five out of six salivary gland tumors. All breast secretory carcinomas were triple negative or weakly ER-positive, and all tumors at both the sites expressed CK5/6 and/or EGFR, consistent with a basal-like phenotype. Sequencing revealed classic ETV6-NTRK3 fusion genes in all cases, including in carcinoma in situ of one breast tumor. Translocations were reciprocal and balanced in six out of nine breast and three out of six salivary gland tumors and were complex in three others. In contrast to most breast basal carcinomas, the mutational burden of secretory carcinomas was very low, and no additional pathogenic aberrations were identified in genes typically mutated in breast cancer. Five (56%) breast and two (33%) salivary gland tumors had simple genomes without copy number changes; the remainder had very few changes, averaging 1.3 per tumor. The ETV6-NTRK3 derivative chromosome was duplicated in one breast and one salivary gland tumor, and was the only copy number change in the latter. The findings highlight breast secretory carcinoma as a subtype more closely related to mammary analog secretory carcinoma than to basal/triple negative breast cancers of no special type. Lack of pathogenic mutations in common cancer-related genes suggests that ETV6-NTRK3 alone may suffice to drive these tumors and likely helps explain their indolent behavior.

Genomic profiling of malignant phyllodes tumors reveals aberrations in FGFR1 and PI-3 kinase/RAS signaling pathways and provides insights into intratumoral heterogeneity.

Malignant phyllodes tumors of the breast are poorly understood rare neoplasms with potential for aggressive behavior. Few efficacious treatment options exist for progressed or metastatic disease. The molecular features of malignant phyllodes tumors are poorly defined, and a deeper understanding of the genetics of these tumors may shed light on pathogenesis and progression and potentially identify novel treatment approaches. We sequenced 510 cancer-related genes in 10 malignant phyllodes tumors, including 5 tumors with liposarcomatous differentiation and 1 with myxoid chondrosarcoma-like differentiation. Intratumoral heterogeneity was assessed by sequencing two separate areas in 7 tumors, including non-heterologous and heterologous components of tumors with heterologous differentiation. Activating hotspot mutations in FGFR1 were identified in 2 tumors. Additional recurrently mutated genes included TERT promoter (6/10), TP53 (4/10), PIK3CA (3/10), MED12 (3/10), SETD2 (2/10) and KMT2D (2/10). Together, genomic aberrations in FGFR/EGFR PI-3 kinase and RAS pathways were identified in 8 (80%) tumors and included mutually exclusive and potentially actionable activating FGFR1, PIK3CA and BRAF V600E mutations, inactivating TSC2 mutation, EGFR amplification and PTEN loss. Seven (70%) malignant phyllodes tumors harbored TERT aberrations (six promoter mutations, one amplification). For comparison, TERT promoter mutations were identified by Sanger sequencing in 33% borderline (n=12) and no (0%, n=8) benign phyllodes tumors (P=0.391 and P=0.013 vs malignant tumors, respectively). Genetic features specific to liposarcoma, including CDK4/MDM2 amplification, were not identified. Copy number analysis revealed intratumoral heterogeneity and evidence for divergent tumor evolution in malignant phyllodes tumors with and without heterologous differentiation. Tumors with liposarcomatous differentiation revealed more chromosomal aberrations in non-heterologous components compared with liposarcomatous components. EGFR amplification was heterogeneous and present only in the non-heterologous component of one tumor with liposarcomatous differentiation. The results identify novel pathways involved in the pathogenesis of malignant phyllodes tumors, which significantly increase our understanding of tumor biology and have potential clinical impact.

Disseminated intravascular large B cell lymphoma with slowly decreasing high-density lipoprotein cholesterol.

Intravascular large B cell lymphoma (IVLBCL) is a rare type of extranodal large B cell lymphoma in the lumina of small vessels. Low high-density lipoprotein cholesterol (HDL-C) is associated with sepsis, malignancy, and death. Recent evidence suggests an inverse relationship between HDL-C and non-Hodgkin lymphoma. We report the case of a 71-year-old female who presented with decreasing HDL-C for years prior to diagnosis of IVLBCL. The patient developed nonspecific symptoms, including dizziness, gait instability, fatigue, tinnitus, and weight loss. Although malignancy was high on the differential, no diagnosis was made antemortem. The diagnosis of disseminated intravascular large B cell lymphoma was made postmortem in multiple organ systems. The presentation of IVLBCL is nonspecific and misleading. To our knowledge this is the second known case report of low HDL-C preceding diagnosis of IVLBCL, but the first case documenting low HDL-C years prior to diagnosis.

Squamous metaplasia of the ovarian surface epithelium and subsurface fibrosis: distinctive pathologic findings in the ovaries and fallopian tubes of patients on peritoneal dialysis.

Peritoneal dialysis is commonly used to treat patients with end-stage renal disease. Patients on long-term peritoneal dialysis develop edema and fibrosis of the peritoneal membrane, but the morphologic effects on the organs of the female genital tract are obscure. We noted squamous metaplasia of the ovarian surface epithelium in a patient on peritoneal dialysis, leading us to review all cases of peritoneal squamous metaplasia in our surgical pathology database. Squamous metaplasia of the peritoneum is rare, and we found only 3 examples. Two cases occurred in women on long-term peritoneal dialysis who were operated on for benign ovarian cystadenomas. The gynecologic pathology findings were similar in both cases, with immature and mature squamous metaplasia present extensively on the surfaces of the ovaries, and in 1 case, on the surface of the ipsilateral fallopian tube. The metaplastic epithelium was keratin and p63 positive. Staining for p63 highlighted areas where the metaplastic epithelium was only 1- or 2-cell layers thick and areas of more developed metaplasia. In addition, there was a broad band of fibrous tissue 1- to 2-mm thick beneath the surfaces. A third case of peritoneal squamous metaplasia involved the serosal surface of the small intestine in a woman who experienced complications after bariatric surgery. There were small nodules of squamous metaplastic epithelium on and beneath the serosal surface of the intestine, surrounded by acute and chronic inflammation and fibrosis. Based on our experience and limited information in the literature, there are 2 distinct patterns of squamous metaplasia of the peritoneum: a diffuse pattern of metaplasia associated with bandlike subsurface fibrosis in peritoneal dialysis patients and a micronodular pattern of metaplasia associated with inflammatory conditions. Dialysis-associated changes involving the ovary and fallopian tube form a mechanical barrier that could contribute to the low rate of fertility in peritoneal dialysis patients.