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The aim of this study was to review the clinicopathologic characteristics of metastatic nonhematopoietic malignancies to the breast, in order to identify salient features for practicing pathologists that are useful in distinguishing metastatic lesions from primary breast neoplasms. A total of 238 cases were identified during the period from January 2005 to January 2015. Clinicopathologic features of these cases were retrospectively reviewed. Primary tumors included melanoma (99, 42%), serous carcinoma (35, 15%), neuroendocrine neoplasm (32, 13%), sarcoma (23, 10%), and adenocarcinoma from various organs (47, 20%), and 2 others. Most metastases were unilateral (223, 94%) and unifocal (206, 87%) and were detected radiographically (167, 70%). Concurrent ipsilateral axillary metastasis occurred in 33 (14%) patients. Among 238 cases, 41 had metastatic disease to the breast concurrently or preceding the primary cancer diagnosis. Notably, in 39 (16%) cases, breast metastasis was the first clinical presentation of disease, and 16 (41%) of these cases were initially misdiagnosed as breast primaries. In contrast, with a known history of nonmammary primary tumors, only 4 of 197 (2%) cases were misdiagnosed (p < 0.0001). Metastatic tumors share many overlapping features with breast primary carcinomas. However, cases with a well-circumscribed tumor, lack of in situ component, estrogen receptor/progesterone receptor negativity, and unusual morphologic features should raise the consideration of metastatic disease. While clinical history is paramount for correct diagnosis, metastasis to the breast as the first clinical presentation is not uncommon., (Copyright © 2022 Elsevier Inc. All rights reserved.)

A diagnostic dilemma can be encountered when primary triple-negative breast carcinoma (TNBC) without an in situ component or metastatic TNBCs lose the currently used organ-specific marker such as GATA3, raising concerns about metastatic carcinoma from other sites. In the current study, we compared the newly identified breast marker TRPS1 with currently used breast markers GATA3 and SOX10 in whole-tissue sections from 315 cases of various subtypes of TNBC. TRPS1 was highly expressed in 100% of triple-negative primary and metastatic invasive lobular carcinomas, 99% of triple-negative primary and metastatic invasive breast carcinoma of no special type (IBC-NST), and 95% of metaplastic breast carcinomas. In contrast, GATA3 and SOX10 were expressed in 94% and 0% of invasive lobular carcinomas, 63% and 74% of IBC-NST, and 50% and 49% of metaplastic breast carcinomas, respectively. For special-type TNBCs, both TRPS1 and GATA3 were negative in acinic cell carcinomas, most cribriform adenoid cystic carcinomas, and neuroendocrine carcinomas, but positive in secretory carcinomas. Triple-negative apocrine carcinoma was the only subtype of TNBC with positive GATA3 but negative TRPS1. These data indicate that TRPS1 is a highly sensitive marker for TNBCs with positivity not only in GATA3/SOX10-positive TNBCs but also in almost all GATA3/SOX10-negative TNBCs., (Copyright © 2022. Published by Elsevier Inc.)

Knowing the sensitivity and specificity of tissue-specific immunohistochemical markers is crucial for accurate determination of the primary tumor site. PAX8 has been used as a diagnostic marker for carcinomas of the gynecologic tract, kidney, and thyroid gland, and CDX2 has been used as a marker of gastrointestinal carcinoma. Neither is considered a marker for breast carcinoma (BC). However, we have encountered BCs that express PAX8 or CDX2, some of which caused diagnostic confusion. We investigated the immunohistochemical staining frequency of PAX8 and CDX2 in BC. We identified 237 BCs for which PAX8 staining results were reported (102 primary and 135 metastatic BCs); seven primary and four metastatic BCs (4.6%) were positive for PAX8, with various intensities and staining patterns. CDX2 staining results were reported for 271 BCs (78 primary and 193 metastatic); four primary BCs and one metastatic BC (1.8%) were positive for CDX2, ranging from focal and weak to diffuse and strong. We also stained primary invasive BCs with PAX8 and CDX2 using tissue microarrays. None of the 332 PAX8-stained cases was positive, while one of 143 CDX2-stained cases was positive. Four PAX8-positive and three CDX2-positive cases were stained with TRPS1, and all were positive for TRPS1. In addition, we reviewed the literature for PAX8 and CDX2 expression in BCs and found 5.5% PAX8-positive BCs (90/1625) in 17 studies and 0.8% CDX-2 positive BCs (7/909) in 20 studies. PAX8 and CDX2 are infrequently expressed in BC by immunohistochemistry, and in rare cases, the staining can be strong and diffuse. Additional diagnostic markers are necessary and helpful in distinguishing breast from other primary origins., (Published by Elsevier Inc.)

When a sarcomatous neoplasm is identified in the breast, distinguishing metaplastic carcinoma, malignant phyllodes tumor (MPT), and primary sarcoma is a diagnostic challenge, especially on small biopsies, as all these tumors may have overlapping morphological features, thoroughly grossing with histological examination and immunohistochemical staining being the standard approach to aid in classifying these lesions. Recently, we identified a highly sensitive and specific breast carcinoma marker TRPS1 with high expression in metaplastic breast carcinoma. In the current study, we tested TRPS1 in MPTs and primary sarcoma of the breast. We found TRPS1 was highly expressed (95%) within spindle cell, chondro-osseous, and/or liposarcomatous components of MPTs, in all breast primary chondrosarcomas and extraskeletal osteosarcomas, but not in other sarcomas of the breast. In extramammary sarcomas, TRPS1 was expressed in 28% of conventional chondrosarcomas and 56% of osteosarcomas of bone, but rarely in undifferentiated pleomorphic sarcomas (UPSs), liposarcomas, and angiosarcomas. In summary, MPTs may share similar genetic background with metaplastic carcinoma exhibiting TRPS1 expression, and TRPS1 may play a role in chondro-osseous differentiation because of its expression in chondro-osseous sarcomas from both breast and extramammary sites. Our findings suggest TRPS1 may be clinically useful in distinguishing MPT and metaplastic carcinoma from primary breast sarcoma except for tumors with chondro-osseous differentiation., (Copyright © 2022 Elsevier Inc. All rights reserved.)

The Dako 28-8, Dako 22C3, and Ventana SP142 assays are among the approved programmed death ligand 1 (PD-L1) immunohistochemical companion/complementary diagnostics associated with cancer treatment. To address the concordance of these assays in triple-negative breast cancer (TNBC), we examined PD-L1 expression in 98 TNBC tumors and compared the positive rates using the three assays and three scoring methods: immune cell (IC), tumor cell (TC), and combined tumor cell and immune cell (TCIC) (an equivalent to combined positive score, or CPS). The positive rate for PD-L1 expression with a 1% cutoff was highest with 28-8, followed by the 22C3. These two assays demonstrated almost perfect or substantial agreement in all three scores. There was less agreement between SP142 and the other assays. Using the IC score or the TCIC score at a 1% cutoff (CPS 1), 4% of tumors were positive for PD-L1 with SP142 but negative with the other assays. Using SP142 with a 1% cutoff as a reference, the optimal cutoff for best agreement was at 1% for IC, 30% for TC, and 2% for TCIC (CPS 2) with the other two assays. A 2% cutoff for the 22C3 TCIC (CPS 2) yielded the best agreement with SP142 1% IC cutoff (kappa 0.65). Our study showed the lowest positive rate with SP142 among the three assays. However, the other two assays were not able to identify all tumors that would test positive with SP142 using IC or TCIC/CPS. It is unlikely to achieve high agreement between SP142 and the other two assays by changing the analytical cutoffs., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Invasive mammary carcinoma with neuroendocrine differentiation has been controversial in terms of its definition and clinical outcome. In 2003, the World Health Organization histologic classification of tumors designated this entity as neuroendocrine carcinoma of the breast and defined mammary neuroendocrine carcinoma as expression of neuroendocrine markers in more than 50% of tumor cells. It is an uncommon neoplasm. Our recent study showed that it is a unique clinicopathologic entity and has a poor clinical outcome compared with invasive mammary carcinoma with similar pathologic stage. Other investigators have also demonstrated a different molecular profile in this type of tumor from that of invasive ductal carcinoma. It is unknown whether the current prognostic markers for invasive mammary carcinoma are also applicable for neuroendocrine carcinoma of the breast. In the current study, we reviewed the clinicopathologic features and outcome data in 74 cases of mammary neuroendocrine carcinoma from the surgical pathology files at The University of Texas, MD Anderson Cancer Center, to identify relevant prognostic markers for this tumor type. As shown previously by univariate analysis, large tumor size, high nuclear grade, and presence of regional lymph node metastasis are adverse prognostic factors for overall survival and distant recurrence-free survival. In the current study, multivariate analysis revealed that overall survival was predicted by tumor size, lymph node status, and proliferation rate as judged by Ki-67 immunohistochemistry. Only nodal status proved to be a significant independent prognostic factor for distant recurrence-free survival. Neither mitosis score nor histologic grade predicted survival in mammary neuroendocrine carcinoma. Our data suggest that routine evaluation of Ki-67 proliferation index in these unusual tumors may provide more valuable information than mitotic count alone., (Copyright © 2011 Elsevier Inc. All rights reserved.)