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Aims Neoadjuvant endocrine therapy (NAET) is used in the management of oestrogen receptor (ER)-positive breast cancer. The optimal method for histological assessment of response and the effect of NAET on the tumour morphology, grade and molecular profile remain unclear. The aim of this study is to investigate the NAET effect on tumour type, grade and molecular profile by analysing a well-characterised cohort of breast cancer samples in a single large UK tertiary referral centre, and to provide guidance on the pathological assessment of those lesions to inform adjuvant management and prognosis. Methods and results A single large-institution cohort of 132 patients who received NAET over a 13-year period was identified. Comprehensive clinical, histopathological and follow-up data were collected. A detailed histological review of a subset with residual post-treatment carcinoma was undertaken. Two carcinomas (both of the lobular type) achieved complete pathological response. Central scarring was seen in 49.3% of tumours post-treatment. Significant changes in tumour type (41.6%), tumour grade (downgrading in one-third of tumours), and progesterone receptor (PR) expression (22.3%), with a switch to PR-negative status in 17.6% of cases, were observed. The last of these was associated with an absence of tumour-infiltrating lymphocytes (P = 0.005). Ten per cent of cases showed a change in HER2 expression (P = 0.002). The median patient survival was 60 months, and downgrading of tumours was associated with better overall survival (P = 0.05). Conclusions We propose a histological method for assessment of residual carcinoma following NAET, and recommend repeat ER/PR/HER2 testing to inform management and prognosis.

The response of human epidermal growth factor receptor2 (HER2)- positive breast cancer (BC) patients to anti-HER2 targeted therapy is significant. However, the response is not uniform and a proportion of HER2-positive patients do not respond. This study aims to identify predictors of response in the neoadjuvant treatment and to assess the discordance rate of HER2 status between pre- and post-treatment specimens in HER2-positive BC patients. The study group comprised 500 BC patients treated with neoadjuvant chemotherapy (NACT) and/or neoadjuvant anti-HER2 therapy and surgery who had tumours that were 3+ or 2+ with HER2 immunohistochemistry (IHC). HER2 IHC 2+ tumours were classified into five groups by fluorescence in situ hybridisation (FISH) according to the 2018 ASCO/CAP guidelines of which Groups 1, 2 and 3 were considered HER2 amplified. Pathological complete response (pCR) was more frequent in HER2 IHC 3+ tumours than in HER2 IHC 2+/HER2 amplified tumours, when either in receipt of NACT alone (38% versus 13%; p = 0.22) or neoadjuvant anti-HER2 therapy (52% versus 20%; p < 0.001). Multivariate logistic regression analysis showed that HER2 IHC 3+ and histological grade 3 were independent predictors of pCR following neoadjuvant anti-HER2 therapy. In the HER2 IHC 2+/HER2 amplified tumours or ASCO/CAP FISH Group 1 alone, ER-negativity was an independent predictor of pCR following NACT and/or neoadjuvant anti-HER2 therapy. In the current study, 22% of HER2-positive tumours became HER2-negative by IHC and FISH following neoadjuvant treatment, the majority (74%) HER2 IHC 2+/HER2 amplified tumours. Repeat HER2 testing after neoadjuvant treatment should therefore be considered.

Extramedullary haematopoiesis (EMH) in the axillary lymph node of breast cancer patients is extremely rare but when encountered can represent a diagnostic challenge. We aim to highlight this incidental finding as a diagnostic pitfall which can be mistaken for metastatic carcinoma (particularly of the metaplastic type). We report the case of a 68-year-old Caucasian female with a family history of cancer. Core biopsy revealed that she had grade II oestrogen receptor-negative, Her2-positive invasive ductal carcinoma. She was offered neoadjuvant chemotherapy with Herceptin and subsequently underwent breast-conserving surgery. Microscopic examination of the post-treatment breast surgical specimen showed a partial pathological response with large areas of tumour regression. The sentinel lymph node showed frequent large single and multinucleate giant cells with hyperchromatic nuclei located predominantly within the subcapsular and medullary sinuses. The morphological differentials of metastatic carcinoma, sinus histiocytosis and extramedullary haematopoiesis were considered. A panel of immunohistochemistry showed these large cells to be negative for epithelial markers and CD68. They were strongly positive for CD42b (megakaryocyte marker). Smaller myeloperoxidase and factor VIII-positive cells were identified. The findings confirmed EMH. Sentinel nodes are often well scrutinised by pathologists for evidence of metastatic carcinoma as an important prognostic parameter both in the standard and neoadjuvant setting. Nodal megakaryocytes have been described in response to neoadjuvant chemotherapy particularly in association with Herceptin treatment. Pathologists’ awareness of this finding in the neoadjuvant setting is crucial to avoid a mistaken diagnosis of malignancy. A relevant immunohistochemical panel together with careful attention to morphology should help establish the correct diagnosis.

The immune microenvironment in inflammatory breast cancer (IBC) is poorly characterised, and molecular and cellular pathways that control accumulation of various immune cells in IBC tissues remain largely unknown. Here, we discovered a novel pathway linking the expression of the tetraspanin protein CD151 in tumour cells with increased accumulation of macrophages in cancerous tissues. It is notable that elevated expression of CD151 and a higher number of tumour-infiltrating macrophages correlated with better patient responses to chemotherapy. Accordingly, CD151-expressing IBC xenografts were characterised by the increased infiltration of macrophages. In vitro migration experiments demonstrated that CD151 stimulates the chemoattractive potential of IBC cells for monocytes via mechanisms involving midkine (a heparin-binding growth factor), integrin alpha 6 beta 1, and production of extracellular vesicles (EVs). Profiling of chemokines secreted by IBC cells demonstrated that CD151 increases production of midkine. Purified midkine specifically stimulated migration of monocytes, but not other immune cells. Further experiments demonstrated that the chemoattractive potential of IBC-derived EVs is blocked by anti-midkine antibodies. These results demonstrate for the first time that changes in the expression of a tetraspanin protein by tumour cells can affect the formation of the immune microenvironment by modulating recruitment of effector cells to cancerous tissues. Therefore, a CD151-midkine pathway can be considered as a novel target for controlled changes of the immune landscape in IBC. (c) 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The prognostic value of the immune cell infiltrate in the breast carcinoma microenvironment is still uncertain. We reviewed published articles analysing the infiltration of inflammatorycells in the microenvironment of breast carcinoma. Data revealed the importance of infiltration of these immune cells in the prognosis of breast carcinoma, particularly the triple-negative and HER2-positive phenotypes. Tumour-infiltrating lymphocytes and their subtypes play a fundamental role in predicting the pathological complete response (pCR) to neoadjuvant chemotherapy. More research aiming to dissect a complex network of communication between cancer cells and other cellular components of the tumour microenvironment is necessary to develop more effective therapeutic approaches.