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Aims CD44, CD24 and ALDH1 are the most consistently used biomarkers to identify and characterise the breast cancer stem cell (CSC) phenotype. However, most studies performed until now analysed samples of invasive ductal carcinomas of no special type (IDC-NST). Therefore, prevalence and clinical significance of these CSC markers in breast carcinomas of special histological types (SHT) is largely unknown. For that reason, this study aims to determine the distribution of the breast CD44, CD24 and ALDH1 CSC markers among a series of invasive breast carcinomas of SHT, in comparison with a series of IDC-NST. Methods 117 invasive SHT breast carcinomas were analysed for the expression of CD44, CD24 and ALDH1, by immuhohistochemistry. The distribution of these CSC markers was evaluated among the distinct histological special types, and the results were compared with a series of 466 IDC-NST. Results The expression prevalence of the breast CSC markers differed between special types and IDC-NST. Medullary, papillary and tubular carcinomas were enriched in the CSC phenotype CD44+/CD24−/low (80.0%, 100.0% and 100.0%, respectively, vs 45.3% in IDC-NST). Considering the ALDH1 cytoplasmic tumour expression, only medullary and metaplastic carcinomas displayed significant increase in CD44+/CD24-/low/ALDH1+ CSC phenotype frequency (36.4% and 28.6%, respectively, vs 4.8% in IDC-NST). Conclusions The expression distribution of breast CSC markers is largely dependent on histological type. Interestingly, within the distinct SHT, medullary and metaplastic carcinomas are the two types highly associated with high-grade carcinomas, basal-like and claudin-low molecular subtypes, and to the CSC phenotype CD44+/CD24−/low/ALDH1+.

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 PIK3 CA 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.

Background Enhancer of zeste homolog 2 (EZH2) is a polycomb-group protein that is involved in stem cell renewal and carcinogenesis. In breast cancer, increased EZH2 expression is associated with aggressiveness and has been suggested to identify normal breast epithelium at increased risk of breast cancer development. However, the association between EZH2 expression in benign breast tissue and breast cancer risk has not previously been evaluated in a large prospective cohort. Methods We examined the association between EZH2 protein expression and subsequent breast cancer risk using logistic regression in a nested case-control study of benign breast disease (BBD) and breast cancer within the Nurses’ Health Studies. EZH2 immunohistochemical expression in normal breast epithelium and stroma was evaluated by computational image analysis and its association with breast cancer risk was analyzed after adjusting for matching factors between cases and controls, the concomitant BBD diagnosis, and the Ki67 proliferation index. Results Women with a breast biopsy in which more than 20% of normal epithelial cells expressed EZH2 had a significantly increased risk of developing breast cancer (odds ratio (OR) 2.95, 95% confidence interval (CI) 1.11–7.84) compared to women with less than 10% EZH2 epithelial expression. The risk of developing breast cancer increased for each 5% increase in EZH2 expression (OR 1.22, 95% CI 1.02–1.46, p value 0.026). Additionally, women with high EZH2 expression and low estrogen receptor (ER) expression had a 4-fold higher risk of breast cancer compared to women with low EZH2 and low ER expression (OR 4.02, 95% CI 1.29–12.59). Conclusions These results provide further evidence that EZH2 expression in the normal breast epithelium is independently associated with breast cancer risk and might be used to assist in risk stratification for women with benign breast biopsies.

In a Perspective, Francisco Beca and Andrew Beck discuss Charles Swanton and colleagues' accompanying Research Article on somatic mutations in patients with inflammatory breast cancer treated in a Phase II clinical trial.

Data on the risk of breast cancer following a benign breast disease (BBD) diagnosis were derived predominantly from populations of women biopsied before the widespread use of mammographic screening and in whom these lesions were mostly incidental findings. Whether or not similar risk associations are seen when these lesions are detected in mammographically screened populations is unknown. To address this, we examined the variation in BBD and breast cancer risk associations by the calendar time of BBD diagnosis (pre- vs. post-mammography era [before vs. 1985 and after]) in a nested case–control study within the Nurses’ Health Study (NHS) and NHSII BBD subcohort (488 cases; 1908 controls). We performed logistic regression analysis, adjusting for matching factors and potential confounders, to estimate odds ratio (ORs) and 95% confidence interval (CI) for the association between BBD subtype (non-proliferative, proliferative without atypia, proliferative with atypical hyperplasia (AH)) and subsequent breast cancer risk. When compared with non-proliferative lesions, both proliferative lesions without atypia (PWA) and AHs were associated with similar levels of risk in the pre-mammographic (pre) and post-mammographic (post) time periods (PWA: OR [95% CI] = 1.73 [1.27, 2.36] pre vs. 1.12 [0.73, 1.74] post; AH: 4.41 [2.90, 6.70] pre vs. 3.69 [2.21, 6.15] post). The interaction by mammography era was not statistically significant ( p -interaction = 0.47). These results suggest that the risk associations reported for BBD subtypes in the pre-mammography era remain valid for BBD detected after the widespread implementation of mammographic screening.

Recurrent mutations in SPOP -encoding a Cullin 3-based E3 ubiquitin ligase- in prostate cancer disrupt the recognition and degradation of ubiquitination substrates, including BET proteins. Consequently, stability of BET proteins is enhanced and this increases the resistance to BET inhibitors in SPOP -mutant prostate tumors. These results, together with those in Janouskova et al. and Zhang et al ., uncover a novel non genetic mechanism of resistance to BET inhibition involving cancer type-specific mutations in SPOP , and support the evaluation of SPOP mutations to inform the administration of BET inhibitors in the clinic. The bromodomain and extraterminal (BET) family of proteins comprises four members—BRD2, BRD3, BRD4 and the testis-specific isoform BRDT—that largely function as transcriptional coactivators 1 , 2 , 3 and play critical roles in various cellular processes, including the cell cycle, apoptosis, migration and invasion 4 , 5 . BET proteins enhance the oncogenic functions of major cancer drivers by elevating the expression of these drivers, such as c-Myc in leukemia 6 , 7 , or by promoting the transcriptional activities of oncogenic factors, such as AR and ERG in prostate cancer 8 . Pathologically, BET proteins are frequently overexpressed and are clinically linked to various types of human cancer 5 , 9 , 10 ; they are therefore being pursued as attractive therapeutic targets for selective inhibition in patients with cancer. To this end, a number of bromodomain inhibitors, including JQ1 and I-BET, have been developed 11 , 12 and have shown promising outcomes in early clinical trials. Although resistance to BET inhibitors has been documented in preclinical models 13 , 14 , 15 , the molecular mechanisms underlying acquired resistance are largely unknown. Here we report that cullin-3 SPOP earmarks BET proteins, including BRD2, BRD3 and BRD4, for ubiquitination-mediated degradation. Pathologically, prostate cancer–associated SPOP mutants fail to interact with and promote the degradation of BET proteins, leading to their elevated abundance in SPOP -mutant prostate cancer. As a result, prostate cancer cell lines and organoids derived from individuals harboring SPOP mutations are more resistant to BET-inhibitor-induced cell growth arrest and apoptosis. Therefore, our results elucidate the tumor-suppressor role of SPOP in prostate cancer in which it acts as a negative regulator of BET protein stability and also provide a molecular mechanism for resistance to BET inhibitors in individuals with prostate cancer bearing SPOP mutations.

The phase 3 KEYNOTE‐522 study in high‐risk early‐stage triple‐negative breast cancer (TNBC) showed significantly improved efficacy outcomes with neoadjuvant pembrolizumab plus chemotherapy followed by adjuvant pembrolizumab versus neoadjuvant chemotherapy alone. We present findings from the KEYNOTE‐522 Japan subgroup. Eligible participants (aged ≥ 18 years) with untreated locally advanced TNBC (stage T1c N1–2 or T2–4 N0–2) were randomized 2:1 to neoadjuvant pembrolizumab 200 mg or placebo plus chemotherapy every 3 weeks for 8 cycles followed by surgery and adjuvant pembrolizumab or placebo for ≤ 9 cycles. Primary endpoints were pathologic complete response (pCR; ypT0/Tis ypN0) at the time of surgery and event‐free survival (EFS). Of 76 participants enrolled in Japan, 45 were randomized to the pembrolizumab arm and 31 to the placebo arm. Median time from randomization to data cutoff (March 22, 2024) was 76.3 months. Twenty‐four participants (53%) in the pembrolizumab arm and 15 (48%) in the placebo arm achieved pCR (between‐treatment arm difference, 4.9%; 95% CI, −17.6% to 27.1%); findings were similar regardless of PD‐L1 expression. Rates of EFS at 60 months were 84% and 73%, respectively (HR, 0.54; 95% CI, 0.20–1.50). Grade 3 or 4 treatment‐related AEs occurred in 37 of 45 participants (82%) treated with pembrolizumab and 23 of 30 participants (77%) treated with placebo; there were no grade 5 AEs. In conclusion, neoadjuvant pembrolizumab plus chemotherapy followed by adjuvant pembrolizumab showed improved efficacy outcomes and manageable safety versus neoadjuvant chemotherapy alone in Japanese participants, supporting the use of this regimen in Japanese patients with high‐risk early‐stage TNBC. Trial Registration: The study (ClinicalTrials.gov, NCT03036488) was conducted in compliance with local and/or national regulations and International Council for Harmonization Good Clinical Practice guidelines and in accordance with the ethical principles originating from the Declaration of Helsinki In the global, phase 3 KEYNOTE‐522 study of high‐risk early‐stage triple‐negative breast cancer (TNBC), neoadjuvant pembrolizumab plus chemotherapy followed by adjuvant pembrolizumab improved efficacy outcomes versus neoadjuvant chemotherapy alone. In this analysis of Japanese participants from KEYNOTE‐522, neoadjuvant pembrolizumab plus chemotherapy followed by adjuvant pembrolizumab improved pCR, along with a trend toward prolonged EFS and OS compared with neoadjuvant chemotherapy alone. These efficacy findings, together with a manageable safety profile, support the use of perioperative pembrolizumab in Japanese patients with high‐risk early‐stage TNBC.

AimsThe clinical significance of radial scar (RS)/complex sclerosing lesion (CSL) with high-risk lesions (epithelial atypia) diagnosed on needle core biopsy is not well defined. We aimed at assessing the upgrade rate to ductal carcinoma in situ (DCIS) and invasive carcinoma on the surgical excision specimen in a large cohort with RS/CSL associated with atypia.Methods157 women with a needle core biopsy diagnosis of a RS/CSL with atypia and follow-up histology were studied. Histological findings, including different forms of the atypical lesions and final histological outcome in the excision specimens, were retrieved and analysed, and the upgrade rates for malignancy and for invasive carcinoma were calculated.Results69.43% of the cases were associated with atypical ductal hyperplasia (ADH) or atypia not otherwise classifiable, whereas lobular neoplasia was seen in 21.66%. On final histology, 39 cases were malignant (overall upgrade rate of 24.84%); 12 were invasive and 27 had DCIS. The upgrade differed according to the type of atypia and was highest for ADH (35%). When associated with lobular neoplasia, the upgrade rate was 11.76%. The upgrade rate’s variability was also considerably lower when considering the upgrade to invasive carcinoma alone for any associated lesion.ConclusionsThe upgrade rate for ADH diagnosed on needle core biopsy with RS is similar to that of ADH without RS and therefore should be managed similarly. RS associated with lobular neoplasia is less frequently associated with malignant outcome. Most lesions exhibiting some degree of atypia showed a similar upgrade rate to invasive carcinoma. Management of RS should be based on the concurrent atypical lesion.

AimsHere we explore the presence of mediator complex subunit 12 (MED12) exon 2 and telomerase reverse transcriptase (TERT) promoter hotspot mutations in complex fibroadenomas (CFAs) of the breast.MethodsThe stromal components from 18 CFAs were subjected to Sanger sequencing of MED12 exon 2 and the TERT promoter hotspot loci. The epithelial and stromal components of two MED12 mutated CFAs were subjected to laser capture microdissection, and Sanger sequencing of MED12 exon 2, TERT promoter and PIK3CA exons 9 and 20, separately.Results MED12 exon 2 mutations were identified in the stroma of 17% of CFAs. The analyses of epithelial and stromal components, microdissected separately, revealed that MED12 mutations were restricted to the stroma. No TERT promoter or PIK3CA mutations in exons 9 and 20 were detected in analysed CFAs.ConclusionsLike conventional fibroadenomas, MED12 exon 2 mutations appear to be restricted to the stromal component of CFAs, supporting the notion that CFAs are stromal neoplasms.

Aims Despite considerable interest in the PI3K/AKT/mTOR pathway in breast carcinomas (BC), published data reports contradictory results regarding the association of phosphorylated mammalian target of Rapamycin (p-mTOR) expression with clinico-pathological features and prognosis in BC. Here, we evaluate the main clinico-pathological associations with p-mTOR expression in BC, with focus on the different molecular subtypes. Methods In this retrospective study, 331 BC patients were included in final analysis. Outcome measures included disease-free survival (DFS) and overall survival (OS) times. Baseline data and outcome measures were compared between immunohistochemical p-mTOR expressing and non-expressing BCs. Subgroup analysis was performed to assess the effect of p-mTOR expression in the outcome for each BC molecular subtype. Results 43.8% of the tumours were positive for p-mTOR, with a significant correlation between p-mTOR expression with smaller (<2 cm) (p=0.021) and lower-grade tumours (p<0.001). Expression of p-mTOR was also associated with longer DFS (HR of 0.32, p<0.001) and OS (HR of 0.20, p<0.001). In a multivariable analysis, the HR remained significant with minimal change (HR=0.26, p=0.002 for OS; HR=0.40, p=0.002 for DFS). In subgroup analysis, luminal p-mTOR-expressing tumours demonstrated longer DFS and OS (HR 0.33, p=0.003; HR 0.20, p=0.003, respectively) independently of size, grade, lymph node status and Her-2 overexpression. Conclusions p-mTOR expression is associated with smaller, lower-grade and with luminal BC. In multivariable analysis, p-mTOR expression was associated with longer DFS and OS, independently of the size, grade and lymph node status, especially in luminal BCs.