Solid Papillary Carcinoma and Encapsulated Papillary Carcinoma of the Breast: Clinical-Pathologic Features and Basement Membrane Studies of 50 Cases

<b><i>Introduction:</i></b> Solid papillary carcinoma (SPC) and encapsulated papillary carcinoma (EPC) of the breast are usually considered in situ lesions due to favorable prognosis, despite the variable presence of myoepithelial cells. We aimed to describe clinical-pathologic features including basement membrane (BM) studies in these tumors. <b><i>Methods:</i></b> Patients diagnosed with SPC and EPC in 2000–2019 were retrospectively identified. Microscopic slides and clinical history were reviewed. Immunohistochemical stains for BM and myoepithelial markers were performed. <b><i>Results:</i></b> Of 23 SPCs and 27 EPCs, there were 5/23 (21.7%) pure SPCs and 9/27 (33.3%) pure EPCs, while 4/23 (17.4%) and 12/27 (44.5%) were associated with ductal carcinoma in situ (DCIS), and 6/23 (26.1%) and 6/27 (22.2%) with invasive carcinoma, respectively; 8/23 (34.8%) SPCs were considered invasive. The median tumor size was 1.7 cm (range 0.1–16). All tumors were positive for hormone receptors and negative for HER2. Myoepithelial cells were absent in 20 tumors (40%) and focally present in 30 (60%). Collagen IV and laminin were negative in most invasive lesions, but they were expressed in 21/21 (100%) and 18/21 (85.7%) of EPCs without invasion, and 16/17 (94.1%) and 10/17 (58.8%) SPCs, including invasive SPCs, respectively. Lymph node involvement was identified in 3/26 (11.5%) patients, including micrometastasis in 1 EPC associated with DCIS, macrometastasis in 1 EPC associated with invasive carcinoma, and isolated tumor cells in 1 invasive SPC. Of 31 patients with outcome data (median follow-up 35 months, range 1–85), 2 (6.5%; 1 SPC, 1 EPC) developed local recurrence, both associated with invasive carcinoma. No distant recurrences or deaths were observed. <b><i>Conclusions:</i></b> Our study confirms favorable prognosis of SPCs and EPCs, with 2 local recurrences occurring in the presence of invasion. SPCs are more commonly associated with invasive carcinoma or considered invasive compared to EPCs (60.9 vs. 22.2%). The presence of BM material and lack of lymph node involvement in most cases indicates that the majority of these tumors may represent in situ lesions; however, some may behave as low-grade invasive malignancy with metastatic potential even in the absence of conventional invasion.

Artefactual Epithelial Displacement in a Papilloma with Extensive Usual Duct Hyperplasia Mimics a Solid Papillary Carcinoma with Invasive Growth

Mammary solid papillary carcinoma and usual duct hyperplasia (UDH) of the breast are morphological look-alikes, characterized by cellular streaming, solid growth, and a lack of high-grade nuclear atypia. Here, we report a challenging papillary lesion in the breast of a 48-year-old woman that presented with a double pitfall. A core needle biopsy showed a solid papillary proliferation of epithelial cells with oval to round overlapping nuclei, surrounded by a sclerotic stroma. This distorted lesion contained peripheral clefts and cellular streaming, without high-grade nuclear atypia. Immunohistochemistry showed diffuse heterogenous immunoreactivity for estrogen receptor and cytokeratin 5, and no immunoreactivity for chromogranin and synaptophysin. The immunohistochemical profile distinguished this sclerosed papilloma with extensive UDH from a solid papillary carcinoma. The lumpectomy specimen revealed a second challenge, where multiple epithelial islets without surrounding myoepithelial cells were observed near the papilloma, mimicking an invasive carcinoma. These islets displayed the same immunohistochemical profile as the sclerosed papilloma and they were surrounded by steatonecrosis and reactive fibroblasts, indicating epithelial displacement within the biopsy needle tract. A sclerosed papilloma with extensive UDH is a morphologically challenging mimic of a solid papillary carcinoma. Immunohistochemistry is helpful to distinguish both entities from one another. Extensive epithelial displacement in the biopsy tract made this case particularly challenging, as the displaced epithelial islets mimicked an invasive carcinoma. Pathologists should be aware of this uncommon double pitfall to prevent misdiagnosis.

Nuclear Insulinoma-Associated Protein 1 Expression as a Marker of Neuroendocrine Differentiation in Neoplasms of the Breast

Insulinoma-associated protein-1 (INSM1), a transcription factor encoded by the insulinoma associated-1 gene, is a second-generation biomarker of neuroendocrine differentiation. Its sensitivity and specificity in comparison with chromogranin-A and synaptophysin have been extensively validated in several organs, but evidence regarding its expression in mammary neoplasms is limited. In this study, INSM1 immunohistochemistry was validated in a cohort of 22 mammary neoplasms, enriched with special type breast carcinomas with known neuroendocrine differentiation as determined by immunohistochemistry for synaptophysin and chromogranin-A. Subsequently, INSM1 expression was evaluated in a consecutive series of 66 invasive breast cancer biopsies. In the validation cohort, 14 tumors were synaptophysin-positive, of which all but one showed INSM1 immunoreactivity. Eight tumors were synaptophysin-negative, of which 3 showed focal nuclear INSM1 expression. Six tumors were chromogranin-A-positive, of which one was INSM1-negative. When compared with synaptophysin, INSM1 seems more sensitive but less specific than chromogranin-A. In the biopsy cohort, only one invasive carcinoma of no special type showed substantial INSM1 immunoreactivity (ie, 25% of the tumor cells). Three more cases showed 1% nuclear INSM1 staining. We conclude that neuroendocrine differentiation in invasive breast carcinoma of no special type is a rare finding. Immunohistochemical biomarkers, comprising INSM1 as well as the first-generation biomarkers chromogranin-A and synaptophysin, are useful to distinguish neuroendocrine differentiation in breast neoplasms. The identification of neuroendocrine differentiation can be helpful to establish the diagnosis of special type breast carcinomas such as solid papillary carcinoma.

Synchronous Bilateral Solid Papillary Carcinoma of Breast: A Rare Case Report

Background: Solid papillary carcinoma is a rare type of carcinoma that accounts for less than 1% of all breast cancers and mostly seen in postmenopausal women. This report presents a rare case of synchronous bilateral solid papillary carcinoma of the breast. Case Report: A 74-year-old female patient had a mass in her right and left breast. Bilateral total mastectomy and sentinel lymph node biopsy were performed. The pathologic diagnosis was synchronous bilateral solid papillary carcinoma. No lymph node metastasis was detected in either of the breasts. Conclusion: To our knowledge, little is known about simultaneous bilateral solid papillary carcinomas. Solid papillary carcinoma should be kept in mind in the differential diagnosis of bilateral breast masses with neuroendocrine differentiation in elderly patients.

Imaging and Histopathology Correlation of Solid Papillary Carcinoma of the Breast : A Review of Four Cases

Solid papillary breast carcinoma is a rare type of breast carcinoma. We present four cases which highlight the radiological and histological findings of solid papillary carcinoma. Mammogram supplemented with ultrasound played an important role in detecting solid papillary carcinomas which usually presents as intraductal lesions or intracystic mass with Doppler signal. Excision biopsy is a better option than core biopsy as the latter modality may not be representative and the diagnosis of solid papillary breast carcinoma may be missed.

Invasive Solid Mucinous Papillary Carcinoma Breast with Neuroendocrine Differentiation: A Case Report with Immunohistochemical Study

Solid papillary carcinoma of the breast (SPCB) is a distinctive form of papillary carcinoma that tends to occur in older women and usually has a favorable prognosis. We describe an invasive solid papillary carcinoma with extracellular and intracellular mucin and neuroendocrine differentiation in a 60-year old female. The cytological features have been also been highlighted with an insight on differentials that were helpful in its correct identification preoperatively.