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 <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<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<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.

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INTRODUCTIONPatients diagnosed with breast cancer (BC) in Brazil are on average 54 years old and the majority (70%) have stage II-III. Age and clinical stage have a negative impact on patient personal life and labor productivity. The socioeconomic status is a fundamental part of the population’s health, which includes marital and employment status. Our aim was to analyze the socioeconomic impact of BC diagnosis which is poorly studied in low or middle-income countries. METHODSThis is a cross-sectional study including patients from AMAZONA III cohort study. Eligible patients were female aged > 18 years with diagnosis of any stage invasive BC from 2016 to 2018 in 24 participating hospitals in Brazil. The present analysis evaluated the marital and employment status at baseline and at 1-year follow-up after BC diagnosis. Patients with missing data were excluded and women older than 60 years, retirement age in Brazil, were not included in this analysis. A multivariate Poisson regression analysis with robust variance was adjusted to assess which patients’ characteristics associated with job loss and relationship status. The characteristics evaluated were age (⇐ 50 vs. > 50 years), educational level (Illiterate to completed first degree or completed second degree vs. higher), personal income (no income – 2 minimum wages vs. 2 to 5 minimum wages vs. more than 5 minimum wages), clinical-stage (I-III vs. IV), molecular subtype (luminal, HER2 positive vs. triple negative), surgery type (breast conserving surgery vs. any type of mastectomy), and systemic treatment (chemotherapy vs. hormonal therapy vs. none). The significance level was set at 5%. All analyses were conducted using SAS version 9.4 (SAS Institute, Cary, NC). RESULTSFrom a total of 1257 patients with evaluable employment status, 655 patients (52.1%) had working activity at the time of BC diagnosis. After 1 year of follow-up, there was an absolute decrease of 5.3% in patients’ employment (52.1% to 46.8%; p= 0.0075). Loss of employment was higher in older patient > 50 years (8.7%), lower educational level (9.9%), those earning 2-5 minimum wages (11.2%), stage I-III (7%), triple negative (6.9%), mastectomy (9.9%) and treatment with hormone therapy (11%). Patients with higher educational level (RR 0.61, 95% CI 0.36-0.94, p=0.0265) were at lower risk of employment loss whereas patients with personal income of more than 2 minimum wages (RR 1.83, 95% CI 1.08-3.10, p=0.0236) and mastectomy (RR 2.16, 95% CI 1.47-3.17, p=0.0015) were at higher risk of being unemployed loss after 1 year of diagnosis. Other factors such as age, clinical stage, BC subtype and treatment were not independently associated with unemployment. A total of 1947 patients had marital status information at baseline. Of those, 1182 (60.7%) were married or in common-law marriage at BC diagnosis. After 1 year of follow-up, 52 (2.7%) of these women loss their relationship (60.7% vs. 58%; p=0.08). Loss of relationships was higher (5.2%) in younger patients (≤ 50 years), lower educational level (4.9%), no income or up to 2 minimum wages (5.4%), stage IV (7.7%), HER2 positive (5.5%), mastectomy (5.4%) and treatment with hormone therapy (5.5%). None of the variables evaluated such as age, educational level, personal income, clinical-stage, molecular subtype, surgery type and systemic treatment, were significantly associated with change of marital status for patients previously married or in common-law marriage. CONCLUSION The socioeconomic impact of BC diagnosis was minimal at 1-year follow-up in Brazil. Nonetheless personal income and surgery type were associated with higher chance of unemployment whereas no specific variables were related to marital status change. Government social policies specifically for work return remains critical for BC patients in short-term after BC diagnosis. Citation Format: Gustavo Werutsky, Daniela Dornelles Rosa, Carlos Barrios, Eduardo Cronemberger, Geraldo Queiroz, Jose Bines, Mahira Lopes Rosa, Rafaela Gomes, Ana P Heck, Laura Freitas, Arthur F da Silva, Matheus Rodrigues, Andre P Fay, Sergio Simon. The socioeconomic impact of breast cancer in Brazil: An analysis of AMAZONA III cohort study [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 PS7-89.

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