Mutations in the ESR1 gene (ESR1m) are important mechanisms of resistance to endocrine therapy in estrogen receptor-positive advanced breast cancer and have been recognized as a prognostic and predictive biomarker as well as a potential therapeutic target. However, the prevalence of ESR1m in real-world patients has not been adequately described. Therefore, we sought to evaluate the prevalence of ESR1m in metastatic samples from Brazilian patients with estrogen receptor-positive (ER+) advanced breast cancer previously treated with endocrine therapy. The presence of ESR1m was evaluated in formalin-fixed paraffin-embedded (FFPE) breast cancer tissue using real-time quantitative polymerase chain reaction (RT-qPCR). Mutations in codons 380, 537, and 538 of the ESR1 gene were analyzed. Out of 77 breast cancer samples, 11 (14.3%) showed mutations in the ESR1 gene. ESR1m were detected in a variety of organs, and the D538G substitution was the most common mutation. In visceral metastasis, ESR1m were detected in 25% (8/32) of the samples, whereas in nonvisceral metastasis, ESR1m were detected in 6.7% (3/45) of the samples. The odds of a sample with visceral metastasis having an ESR1 mutation is 4.66 times the odds of a sample of nonvisceral metastasis having an ESR1 mutation (95% CI: 1.13–19.27; p value = 0.0333). Our study indicates that the prevalence of ESR1m in samples from Brazilian patients with metastatic ER+ breast cancer is similar to that described in patients included in clinical trials. We observed an association of ESR1m with visceral metastasis.

Introduction: Mutations in the ESR1 gene (ESR1m) are important mechanisms of resistance to endocrine therapy in estrogen receptor-positive (ER+) metastatic breast cancer and have been studied as a potential therapeutic target, as well as a predictive and prognostic biomarker. Nonetheless, the role of ESR1m as a possible mechanism of primary endocrine resistance, as well as whether it also occurs in tumors that are resistant to ET administered in early-stage disease as (neo)adjuvant, has not been adequately studied. In this study, we evaluated the prevalence of ESR1m in tumor samples from patients with ER+ breast cancer resistant to neoadjuvant aromatase inhibitor therapy. Methods: We followed a prospective cohort of patients with ER+ HER2-stages II and III breast cancer treated with neoadjuvant endocrine therapy (NET). Tumor samples from patients with a pattern of primary endocrine resistance [defined as a Preoperative Endocrine Prognostic Index (PEPI) score of ≥4] were identified and analyzed for the presence of ESR1m. Results: One hundred twenty-seven patients were included in the cohort, of which 100 (79%) had completed NET and underwent surgery. Among these patients, the PEPI score ranged from 0 to 3 in 70% (70/100), whereas 30% (30/100) had a PEPI score of 4 or more. Twenty-three of these patients were included in the analysis. ESR1 mutations were not identified in any of the 23 patients with early-stage ER+ breast cancer resistant to NET. Reinert et al. ESR1m After Neoadjuvant Endocrine Therapy Discussion: Growing evidence supports the notion that there are different mechanisms for primary and secondary endocrine resistance. Our study suggests that ESR1 mutations do not evolve rapidly and do not represent a common mechanism of primary endocrine resistance in the neoadjuvant setting. Therefore, ESR1m should be considered a mechanism of acquired endocrine resistance in the context of advanced disease. Further research should be conducted to identify factors associated with intrinsic resistance to ET.

Objetivo: O câncer de mama negativo triplo (triple negative breast cancer -TNBC) é um subtipo de tumores com biologia intrínseca agressiva, resultando em pior prognóstico. O receptor de andrógeno (androgen receptor -AR) é atualmente um dos biomarcadores mais estudados em TNBC, desempenhando papel na gênese e no desenvolvimento do câncer de mama. Métodos: Neste estudo transversal, revisamos retrospectivamente os registros médicos de todos os pacientes com TNBC que receberam atendimento de 2012 a 2014 em um único centro no sul do Brasil. O material histológico dos tumores de mama foi analisado por imuno-histoquímica para a expressão de AR e relacionado a idade, grau histológico, linfócitos infiltrantes de tumores (TILs) e Ki-67. Resultados: Dos 34 casos identificados de TNBC, 23 (67,6%) eram AR negativos e 11 (32,4%), AR positivos. A idade média foi de 51,9 anos (30-82 anos). Entre os casos positivos, AR foi fracamente expresso em 6 e fortemente expresso em 5 casos. A maioria dos pacientes (n=28, 82,0%) apresentou tumores pouco diferenciados. A expressão média de Ki-67 foi de 65,0% em AR-negativo e 43,6% em AR-positivo (p<0,05). Houve associação significativa entre a idade e a expressão de AR (p<0,005), associada à idade média de 70,8 anos no grupo Androgen receptor (AR) is currently one of the most studied biomarkers in TNBC, playing a role in the genesis and development of breast cancer. Methods: In this cross-sectional study, we retrospectively reviewed the medical records of all patients with TNBC who received care from 2012 to 2014 at a single health center in southern Brazil. Histological material from breast tumors was analyzed by immunohistochemistry for AR expression and related to age, histological grade, tumor-infiltrating lymphocytes (TILs), and Ki-67. Results: Of 34 TNBC cases identified, 23 (67.6%) were AR negative and 11 (32.4%) were AR positive. The average age of the patients was 51.9 years (range: 30-82 years). Among positive cases, AR was weakly expressed in 6 and strongly expressed in 5 cases. Most patients (n=28; 82.0%) had poorly differentiated tumors. Mean Ki-67 expression was 65.0% in AR-negative and 43.6% in AR-positive cases (p<0.05). There was a significant association between age and AR expression (p<0.005), which was associated with mean age 70.8 years in the strongly AR-positive group and 42.3 years in the weakly AR-positive group. The mean percentage of TILs was 38.6% in AR-positive and 39.1% in AR-negative cases (p=0.391). Conclusion: There was no significant association between AR expression and histological grade or TILs. AR positivity in TNBC was associated with older age and tumors with lower Ki-67 expression, indicating two subgroups with distinct phenotypes in patients with TNBC.

INTRODUCTION Current definition of HER2-positive BC follows ASCO/CAP guidelines using immunohistochemistry (IHC) and/or in situ hybridization (ISH)-based techniques. However, HER2 expression can be variable in cells that lack ERBB2 amplification. For example, HER2-negative tumors can express some level of HER2 protein by IHC (i.e. 1+ or 2+ and a negative ISH result) and are identified as HER2-low. Others have no expression and are considered HER2-zero. Innovative therapies have shown promising activity in patients in HER2-low BC. The aim of this study is to evaluate the association of HER2-low and HER2-zero status with response to NACT in HER2-negative BC. METHODS Retrospective cohort of patients with HER2-negative BC treated with NACT in four institutions in Brazil. Protocols of diagnosis, treatment and follow-up were standardized and based on international guidelines. Tumors with HER2 IHC score 0 were classified as HER2-zero whereas tumors with HER2 score 1+ and those with HER2 score 2+ with FISH-negative were classified as HER2-low. Patients were treated with anthracycline- and taxane- based chemotherapy. The following clinicopathological data were evaluated, when available: age, ER, Ki67, tumor size, lymph node (LN) status and response to NACT according to pCR status and residual cancer burden (RCB) index. Primary objective was to evaluate the prevalences and compare pCR rates among HER2-zero and HER2-low cases. Secondary objectives were to perform the same comparison within the HR-positive (HR+) and HR-negative subgroups. Pearsons chi squared tests were performed and a p value of &lt;0.05 was considered statistically significant. RESULTS 331 patients were included in this analysis. 63% were HR+and 37% were TNBC. 50% were HER2-zero and 50% HER-low (36% HER2 IHC 1+ and 14% HER2 IHC 2+/FISH-negative). Median age, initial tumor size, clinical LN status and Ki67 expression were similar among HER2-zero and HER2-low subgroups. In HR+ tumors, 42% (86/207) were HER2-zero and 58% (121/207) were HER2-low. In TNBC, 63% (78/124) were HER2-zero and 37% (46/124) were HER2-low (p&lt;0.001, Pearsons chi squared test). The pCR rate was 26% (85/331) in the entire cohort. As expected, there was a higher rate of pCR in TNBC vs HR+ (50% vs 11%, p&lt;0.001). We found a statistically significant difference in the pCR rates when comparing the HER2-zero versus HER2-low subgroups (31% vs 20%, p=0.03). However, this difference is mostly related to an imbalance between groups (HER2-zero subgroups had a higher proportion of TNBC). Among HR+ tumors, there was no difference in the pCR rates between HER2-zero and HER2-low subgroups (8% vs 13%, p=0.35). In TNBC, we identified an interesting but non-statistically significant difference in pCR in HER2-zero vs. HER2-low tumors (56% vs. 39%, p=0.09). In the TNBC cohort we identified a non-statistically significant difference in RCB 0-I in HER2-zero vs. HER2-low tumors (p=0.06). With a 30 month median follow-up, PFS and OS data are immature. CONCLUSION The distribution of HER2-zero and HER2-low cases is different in HR+ and TNBC. HER2-low is more frequent in HR+ and HER2-zero in TNBC. We identified a higher pCR rate in HER2-zero compared to HER2-low tumors, even though this difference is associated with an imbalance between the two groups. Still, we identified a trend to higher pCR rate in HER2-zero compared to HER2-low tumors even within the TNBC subgroup. Identification of HER2-low and HER2-zero tumors may have clinical implications that should be further explored. Citation Format: Tomas Reinert, Guilherme Parisotto Sartori, Alessandra AB Souza, Rodrigo Pellegrini, Mahira L Rosa, Nathalia Rossatto, Guilherme P Coelho, Isnard E Litvin, Felipe Zerwes, Eduardo Millen, Francisco P Cavalcante, Antonio L Frasson, Marcia S Graudenz, Carlos H Barrios. Prevalence of HER2-low and HER2-zero subgroups and correlation with response to neoadjuvant chemotherapy (NACT) in patients with HER2-negative breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS4-22.

Question: A 60-year-old man sought care for diarrhea with mucus, fever, dehydration, and weight loss after eating raw fish. He presented sepsis with colonic distension on a computed tomography scan. Laboratory results were as follows: creatinine 1.2 mg/dL, magnesium 1.2 mg/dL, potassium 3.1 mg/dL, albumin 1.4 mg/dL, sodium 131 mg/dL, and bicarbonate 15.9 nmol/L. After 10 days of cefepime, his fever, mucus, and colonic distension resolved. He persisted with weight loss and watery diarrhea, however. Fecal analysis of bacterial, viral and parasitical infections were negative. Enteric magnetic resonance imaging (EMRI) was performed (Figure A). What is the most likely diagnosis and how should the attending physician proceed? Look on page 27 for the answer and see the Gastroenterology web site (www.gastrojournal.org) for more information on submitting your favorite image to Clinical Challenges and Images in GI.