Low-volume SLN disease after NAC is not an indicator of a low risk of additional positive axillary nodes and remains an indication for ALND, even when not detected on intraoperative FS.

False-negative (FN) intraoperative frozen section (FS) results of sentinel lymph nodes (SLN) have been reported to be more common after neoadjuvant chemotherapy (NAC) in the primary surgical setting. We evaluated SLN FS assessment in breast cancer patients treated with NAC to determine the FN rate and the histomorphologic factors associated with FN results. Patients who had FS SLN assessment following NAC from July 2008 to July 2017 were identified. Of the 711 SLN FS cases, 522 were negative, 181 positive, and 8 deferred. The FN rate was 5.4% (28/522). There were no false-positive results. Of the 8 deferred cases, 5 were positive on permanent section and 3 were negative. There was a higher frequency of micrometastasis and isolated tumor cells in FN cases (P<0.001). There was a significant increase in tissue surface area present on permanent section slides compared with FS slides (P<0.001), highlighting the inherent technical limitations of FS and histologic under-sampling of tissue which leads to most FN results. The majority (25/28, 89%) of FN cases had metastatic foci identified exclusively on permanent sections and were not due to a true diagnostic interpretation error. FN cases were more frequently estrogen receptor positive (P<0.001), progesterone receptor positive (P=0.001), human epidermal growth factor receptor-2 negative (P=0.009) and histologic grade 1 (P=0.015), which most likely reflects the lower rates of pathologic complete response in these tumors. Despite its limitations, FS is a reliable modality to assess the presence of SLN metastases in NAC treated patients.

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Breast lymphoma (BL) is a rare entity representing 1%-2% of breast malignancies while being the most common extra-mammary cancer involving the breast. It primarily affects postmenopausal women with a similar clinical presentation as breast carcinoma. It is classified into two main categories: primary breast lymphoma (PBL), and secondary breast lymphoma (SBL) as part of systemic disease. Bilateral breast involvement is not an uncommon situation and was reported in 0%-25% of patients with PBL in the previous series. Overall, the most common histologic subtype is diffuse large B-cell lymphoma (DLBCL), followed by extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) and follicular lymphoma. 1,2 The prevalence of a history of breast carcinoma (BC) in patients with BL was not well documented and reported mostly as single case reports. The recommended treatment modality for patients with BL differs from BC and includes chemotherapy ± radiotherapy. When a definitive diagnosis and pathologic subtyping of BL are made on core biopsy, surgery is usually not recommended and has no impact on survival in most cases. A variety of clinical and pathologic characteristics such as age, stage, type of treatment, or pathologic subtype were observed to impact the prognosis of patients with BL. 1,2 However, the significance of history of BC for the prognosis of BL has not been explored in previous studies. In this study, we aimed to report a single health care system experience in BL with a specific focus on patients with a history of BC. | ME THODSAfter obtaining approval from the Northwell Health Institutional Review Board, our health system's pathology database was searched from January 1, 2010, to July 31, 2020, for lymphoid neoplasms involving the breast that were diagnosed on core needle biopsy, excision, mastectomy, or implant removal. Clinical, radiology, and pathology notes were reviewed to note the following: age, sex, history of BC, axillary involvement, side of involvement, radiologic characteristics and size, BIRADS score, type of procedure, pathological

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Spindle cell lesions of the breast are rare entities and pose a diagnostic challenge for pathologists due to overlapping morphologic and immunohistochemical features. We evaluated EZH2 expression in various benign (fibromatosis (n = 8), myofibroblastoma (n = 7), neurofibroma (n = 1), nodular fasciitis (n = 5), benign phyllodes tumor (n = 18)) and malignant (malignant phyllodes tumor (n = 8), metaplastic breast carcinoma (n = 16) and angiosarcoma (n = 8)) spindle cell lesions as a potential diagnostic and therapeutic marker. The EZH2 expression was evaluated semi‐quantitatively to categorize the cases as ‘low’ and ‘high’ expression. All benign lesions showed low EZH2 expression, whereas high EZH2 expression was observed in the majority (28/32; 88%) of malignant lesions. The study results suggest that EZH2 may be used both as an additional diagnostic tool to reach an accurate diagnosis of the spindle cell lesions of the breast and as a therapeutic target for the malignant lesions.

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