Abstract OT2-22-02: Sequencing of anthracyclines and taxanes during neoadjuvant therapy of locally advanced HER2-negative breast cancer (NEOSAMBA Study/LACOG 0419)

Background: Breast cancer (BC) is the most frequent cancer in women in Brazil, with more than 60,000 cases estimated annually. Forty percent of patients present with stages III and IV and neoadjuvant chemotherapy (NACT) remains the mainstay of treatment for locally advanced breast cancer (LABC). Taxanes usually follow anthracyclines in breast cancer neo/adjuvant treatment, likely because of their later introduction into clinical practice. However, the potential impact of alternative sequencing remains to be studied. A single-center phase II randomized clinical trial conducted in the Brazilian National Cancer Institute showed an improvement in overall survival with taxane-first compared with anthracycline-first sequencing in HER2-negative LABC (Bines J et al, The Oncologist 2020). As a taxane-before-anthracycline sequence carries neither an incremental cost nor increased toxicity, the optimal sequencing of these agents could have significant implications for clinical practice. To confirm this finding, we are currently conducting a multicenter randomized phase III trial comparing a taxane followed by an anthracycline-based regimen with the reverse sequence in the neoadjuvant setting. Trial Design: This randomized, open-label, phase III trial will be conducted in 15 research centers in Brazil. It was approved by the local ethics committee in 2020 and is registered in Clinicatrials.gov with the identifier NCT04540692. Women with HER2-negative LABC are randomized in a 1:1 ratio to anthracycline-before-taxane (AC-T arm) or taxane-before-anthracycline (T-AC arm), stratified by hormone receptor status (positive vs. negative) and axillary lymph node status (N0 vs. N+). The anthracycline-based therapy recommended in this trial is AC (doxorubicin 60 mg/m2 and cyclophosphamide 600 mg/m2) every three weeks for four cycles, whilst the taxane-based therapy is either weekly paclitaxel 80 mg/m2 weekly for 12 weeks, paclitaxel 175 mg/m2 every three weeks, or docetaxel 75-100 mg/m2 every three weeks. The use of carboplatin concomitantly with taxane for triple-negative tumors and dose-dense regimens is allowed following institutional guidelines. Further therapies (surgery, radiotherapy, and endocrine therapy) are performed according to the physicians’ discretion. Tumor samples are collected and stored for translational studies. Eligibility: Inclusion criteria: women ≥18 years of age; histologically confirmed HER2-negative breast cancer (by ASCO/CAP guidelines); stage ≥ IIB (if TNBC) or ≥ III (if HR-positive); PS ECOG 0-2 and adequate organ function. Exclusion criteria: previous use of anti-cancer therapies; bilateral BC and pregnancy. Specific Aims: The primary objective is invasive disease-free survival (iDFS). Secondary objectives include pathological complete response (pCR) rates, overall survival (OS) and safety. Statistical Methods: Considering an unicaudal type I error of 0.05, a type II error of 0.2, and an estimated iDFS of 50% in 5 years in the control arm, a total of 227 evaluable patients should be included per arm to demonstrate a HR of 0.7 favoring the taxane-first arm. Estimating a dropout rate of 10%, 494 patients will need to be included in the study. Present Accrual and Target Accrual: A total of 9 sites of 15 planned are activated. The first patient was enrolled on January 12, 2021, and as of June 24, 2022, a total of 113 patients have been accrued. The target goal of 494 patients is expected to be achieved by 2025 and initial study results will be reported by 2026. Funding: Brazilian Health MInistry, Programa Nacional de Apoio à Atenção Oncológica (PRONON), NUP 25000.183207/2019-50. Acknowledgements: CURA Project, SAS.

Citation Format: Tomás Reinert, Cristiano P. Souza, Pedro Liedke, Gustavo Werutsky, Laura Testa, Vivian Antunes, Carlos Barrios, Vivian Vasconcelos, Heloísa Resende, Geraldo Silva Queiroz, Gisah Guilgen, Yeni Nerón, Lilian Arruda Bastos, Sabina Aleixo, Daniel Cubero, Maria Cristina F. Magalhães, Ana Coradazzi, Daniela Galvão B. de Oliveira, João S. Nunes, Rafaela G. Jesus, Gustavo Gössling, José Bines. Sequencing of anthracyclines and taxanes during neoadjuvant therapy of locally advanced HER2-negative breast cancer (NEOSAMBA Study/LACOG 0419) [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT2-22-02.

Abstract OT3-07-01: Real-World Data on First-line Treatment of HR-positive, HER2-negative, Metastatic Breast Cancer in Brazil (BRAVE Study/LACOG 0221)

Background: It is estimated that 50 thousand patients live with metastatic breast cancer (MBC) in Brazil. A recent Brazilian registry (LACOG 0312) on MBC demonstrated a median overall survival (OS) by breast subtype of 15 months for triple negative, 23 months for HER2 positive, and 42 months for Luminal tumors, which are very similar to developed countries except the HER2 positive group which have limited access to targeted agents in the public health system. Recently, CDK 4/6 inhibitors were approved for the treatment of HR+ HER2-negative MBC with an improvement in progression-free survival (PFS) and ribociclib and abemaciclib demonstrating benefit in OS over endocrine therapy alone, establishing the standard of care in first-line setting for this BC subtype. In Brazil, disparities exist in the incorporation of novel anticancer agents between public and private health systems limiting treatment options for patients with HR+ HER2- negative MBC in the public system, which covers most of the population. The BRAVE study aims to describe the patient journey and current patterns of care for HR+ HER2-negative MBC to identify possible gaps and how health insurance type influences treatment patterns in Brazil. Trial Design: This is an observational, retrospective cohort study. All patients diagnosed with mBC (either de novo or recurrent) in the period of January 2018 to December 2020 at participating centers will be included. Data will be collected from medical records. No interventions are proposed. Enrollment of a total of 300 patients (150 patients from public health care system and 150 patients from private health care system) is planned. ClinicalTrials.gov identifier: NCT05034393. Eligibility: Inclusion criteria: women ≥18 years old; histologically confirmed HR-positive HER2-negative invasive breast cancer; HR-positive, defined as 1% to 100% of tumor nuclei positive for ER and/or PgR as per ASCO/CAP Guideline 2020 or Allred score of ≥3; HER2-negative, defined as IHC result is 0/1+ or 2+ with ISH negative as per ASCO/CAP Guideline 2018; diagnosed with de novo or recurrent metastatic breast cancer between January 2018 and December 2020. Exclusion criteria: male BC; first-line treatment for mBC received through clinical trial. Specific Aims: Primary objective is to describe the first-line (1L) treatment of HR-positive, HER2-negative mBC in Brazil. Secondary objectives are to describe progression-free survival (PFS) in the 1L setting until month 24; describe and compare the 1L treatment of HR-positive, HER2-negative mBC and PFS until month 24 according to the health care coverage (public vs. private); describe timelines from symptoms, histopathological diagnosis, molecular test, and treatment; describe the mBC pathological characterization; describe frequency of diagnostic tests to define breast cancer molecular subtypes; describe the subsequent line of treatment and corresponding PFS; describe overall survival (OS); evaluate PFS and OS according to visceral vs. non-visceral metastatic disease, primary endocrine resistance vs. acquired endocrine resistance, de novo versus recurrent disease, public vs. private health system and pre vs postmenopausal status. Statistical Methods: No a priori sample size calculation was performed. The expected sample size of 150 patients in each group allows description of the proportion of patients using CDK 4/6 inhibitors with two-sided 90% confidence interval ranging from 53.4% to 66.6% when the expected proportion is 60% in the private health system. Present Accrual and Target Accrual: A total of 12 sites of 14 planned were activated. The first patient was enrolled on February 8, 2022. As of June 24, 2022, a total of 122 patients were enrolled, 86 from public and 36 from private health system. The target accrual of 300 patients is expected to be completed by November 2022. Results are expected to be presented by April 2023. Funding: Novartis. Acknowledgements: SAS.

Citation Format: Gustavo Werutsky, Tomás Reinert, Daniela D. Rosa, Romualdo Barroso-Sousa, Heloísa Resende, Poliana A. Signorini, Juliana G. Martins Fagundes, Jose Marcio B. Figueiredo, Eduardo Cronemberger, Aline C. Vieira, Jorge Henrique Santos Leal, Luiza Nardin Weis, Ludmila Thommen, Rafaela G. Jesus, Gustavo Gössling, José Bines. Real-World Data on First-line Treatment of HR-positive, HER2-negative, Metastatic Breast Cancer in Brazil (BRAVE Study/LACOG 0221) [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT3-07-01.

Advanced Stage at Diagnosis and Worse Clinicopathologic Features in Young Women with Breast Cancer in Brazil: A Subanalysis of the AMAZONA III Study (GBECAM 0115)

PURPOSE

Breast cancer (BC) in young women is uncommon and tends to present with more aggressive characteristics. To better understand and characterize this scenario in Brazil through real-world data, we performed a subanalysis of AMAZONA III study (ClinicalTrials.gov identifier: NCT02663973).

METHODS

The AMAZONA III study (GBECAM 0115) is a prospective registry that included 2,950 women newly diagnosed with invasive BC in Brazil from January 2016 until March 2018 at 22 sites. Valid data were obtained from 2,888 patients regarding age at diagnosis and complete baseline information. To compare epidemiologic and clinicopathological features at the time of diagnosis, patients with BC were divided into two groups according to age: ≤ 40 years and > 40 years. Quantitative variables were described as means, and categorical variables were described as frequencies and percentages and compared using the Pearson’s χ² test.

RESULTS

Of 2,888 women diagnosed with BC, 486 (17%) were ≤ 40 years old. Young women had higher educational level, most were employed and a significant number were married (P < .001 for all associations). Younger patients were more symptomatic at BC diagnosis (P < .001), and they also presented more frequently with stage III, T3/T4, grade 3 tumors, HER-2–positive, luminal B, and triple-negative subtypes.

CONCLUSION

Brazilian women younger than age 40 years have unfavorable clinicopathological features of BC at diagnosis, with more aggressive subtypes and advanced stage when compared with older women. These differences are not explained by socioeconomic or ethnic imbalances. The causes of a higher prevalence of BC among young women in Brazil deserve additional investigation.

120 Use of fixable dyes to analyze equine sperm membrane integrity and acrosome reaction after A23187 treatment

Conventional IVF is not successful in the horse, and current work is focused on factors affecting sperm capacitation in this species. Challenges arise in assessing equine sperm incubated in media containing capacitation promotors, as some of these factors cause sperm head-to-head binding (aggregation). Our preliminary microscopic findings showed that sperm aggregates are largely of viable sperm, whereas nonviable sperm individualize. Thus, data obtained using technologies that analyse only individual cells and gate out aggregates, such as flow cytometry, may not accurately represent the study population. We developed a fixable live/dead/acrosome staining protocol (LD-PSA) that minimizes sperm aggregation. The aim of this study was to evaluate the percentage of viable and acrosome-reacted equine sperm after A23187 treatment, using either LD-PSA or a standard staining protocol (PI-PSA). Sperm from 9 ejaculates were suspended in Hanks’ balanced salt solution (HBSS) and exposed for 10min at 37°C to vehicle (V) or to 10 µM A23187 (C10). The sperm were washed, resuspended in HBSS medium with added lactate and pyruvate and containing 7mgmL−1 of bovine serum albumin (BSA), and assessed immediately (0h) or incubated at 37°C for 2h (the period needed for equine sperm to respond to A23187). Motility was analysed using computer-assisted semen analysis. Each treatment was stained by PI-PSA: propidium iodide and fluorescein isothiocyanate-Pisum sativum agglutinin (PSA) in DPBS; and by LD-PSA: Live/Dead Fixable Red, paraformaldehyde 2%, Triton×1%, and FITC-PSA in Dulbecco's phosphate-buffered saline with Accumax (Stem Cell Technologies), a commercial proprietary cell agglutination inhibitor, before flow cytometric analysis. Differences were analysed using repeated-measures two-way ANOVA. The% total motile sperm (TMOT) for V and C10 treatments were 76.3±3.0 and 71.2±4.7 at 0h (P&gt;0.05), and 70.5±14.8 and 2.4±0.8 at 2h (P&lt;0.05). On flow cytometry, the percentage of events outside the gate for V sperm (0h and 2h combined) was 31.9% in PI-PSA and 21.9% in LD-PSA samples (P&lt;0.01). Measured viability in V samples was significantly lower when stained with PI-PSA than with LD-PSA at 0h (49.2±4.6 vs. 67.1±4.9) and tended to be lower (P=0.07) at 2h (44.0±4.9 vs. 55.1±2.8). Notably, the viability recorded in PI-PSA was 26 percentage points lower than was the TMOT at both 0h and 2h, indicating nonrepresentative results, as nonviable sperm should not be motile. By LD-PSA, this difference was 9 points at 0h and 15 points at 2h. Vehicle sperm showed significantly higher AR values in PI-PSA than in LD-PSA at 0h (30.4±4.0 vs. 17.7±2.4) and 2h (41.9±4.5 vs. 24.0±1.8), as did C10 sperm at 0h (28.9±2.7 vs. 18.0±2.5). The lower values for viability than total motility likely reflect agglutination of viable sperm and thus their exclusion from analysis on flow cytometry. The anti-clumping measures employed in the LD-PSA protocol were associated with increased correspondence of measured viability with TMOT. Thus, LD-PSA may offer a more accurate technique to assess viability and acrosome status of equine sperm incubated in capacitating conditions.

121 Effect of pentoxifylline on motility of good- and poor-quality frozen-thawed equine sperm

Equine semen used for intracytoplasmic sperm injection (ICSI) is typically frozen-thawed and may be of poor quality. To prepare sperm for ICSI, semen is typically centrifuged to remove freezing extender. However, centrifugation can cause damage to sperm, which is especially meaningful if sperm quality is already poor. We evaluated a method for selection of sperm without centrifugation, using a “swim-over” technique, and assessed the effect of pentoxifylline, a phosphodiesterase inhibitor that increases sperm motility in other species. To mimic poor-quality semen, we thawed frozen semen (1×) and re-froze it three additional times (4×). Aliquots (0.25 µL; 50,000 sperm) of 1× or 4× semen were placed at the bottom of the right leg of an “H,” made using 15µL of medium by tracing a template placed below a Petri dish. The medium used (Hanks’ balanced salt solution with 40mg mL BSA and added lactate and pyruvate) contained different concentrations of pentoxifylline (0, 0.5, 1, 2 or 4mgmL−1). One µL of medium was removed from the tip of the left arm of the H after 15 and 30min incubation, and the number of sperm were counted. In a second study, we evaluated the effect of pentoxifylline on sperm motility parameters using computer-assisted sperm motility analysis. After thawing, 1× and 4× semen was washed to remove freezing extender and resuspended in the same medium but with 7mgmL−1 bovine serum albumin (BSA), containing the different pentoxifylline concentrations. In Study 1, the number of collected sperm did not differ significantly for 1× sperm exposed to 0 to 4mgmL−1 pentoxifylline (means of 15 to 23 sperm at 15min, and 18 to 25 sperm at 30min). Similarly, in 4× frozen semen, there was no significant difference in number of collected sperm between 0mgmL−1 and 2 or 4mgmL−1 pentoxifylline concentrations (&lt;1 to 6 at 15 min; 5 to 6 at 30min). In Study 2, at 0min,% total motility was significantly higher in 1 and 2mgmL−1 pentoxifylline than in 0mgmL−1 for 1× sperm (47.8±1.7 and 49.3±1.9, vs. 32.1±3.9, respectively; P=0.018) and significantly higher for 1, 2, and 4mgmL−1 pentoxifylline than for 0mgmL−1 for 4× sperm (3.9±0.9, 5.7±0.4, and 8.2±0.5, vs. 1.2±0.4; P=0.0001). Similar results were found at 15 and 30min for 1×, and at 15min for 4×. Pentoxifylline at 1 to 4mgmL−1 significantly increased the percentage of progressive motility in 1× sperm at 30min (17.8±1.3, 21.8±2.7, and 20.3±1.2, vs. 10.0±0.4; P=0.002) and, at 4mgmL−1, increased the percentage of progressive motility in 4× sperm at 0min (1.43±0.1 vs. 0.2±0.1; P=0.005) and 15min (1.4±0.2 vs. 0.1±0.0; P=0.0001). Exposure of poor-quality semen to pentoxifylline at 4mgmL−1 improved total and progressive motility but did not increase the recovery of motile sperm in a swim-over collection preparation.

Abstract P1-08-27: Advanced stage at diagnosis and worse clinicopathologic features in young woman with breast cancer. A sub-analysis of Brazilian population through the AMAZONA III study (GBECAM 0115)

BACKGROUND: Breast cancer (BC) in young women is uncommon and often more aggressive. There are disparities in terms of screening coverage, diagnostic features and access to optimal treatment among young BC patients worldwide. To better understand this scenario through real world data we performed a sub-analysis of AMAZONA III study. METHODS: The AMAZONA III study (GBECAM 0115) is a prospective registry that included 2950 women newly diagnosed with invasive BC in Brazil during the period of January 2016 to March 2018 within 22 sites. Of them, 2888 patients had valid data regarding age at diagnosis and complete baseline information. For the purpose of comparisons of epidemiologic and clinicopathologic features at the time of diagnosis of BC, patients were divided in two groups: women aged ≤40 years (Group 1) and &gt;40 years (Group 2). Quantitative variables were expressed with mean, while categorical variables were described as their count and percentage and compared using the chi-square test. RESULTS: Of 2888 women, 486 (17%) were ≤40 years of age. No differences were found between ethnicity, performance status, body mass index, personal income, health insurance and family history of cancer between the two groups. Young women had higher educational level (p&lt;0.001), were more involved into a labor activity (p&lt;0.001) and were more frequently married (p&lt;0.001). There were also significant differences regarding nulliparity (p&lt;0.001) and previous use of oral contraceptives (p&lt;0.001). Mode of detection of BC was symptomatic in 73.4% of young group versus 64.5% in older group and screen-detected was only 26.6% vs. 35.5% respectively (p&lt;0.001). Table 1 describes clinicopathological characteristics of the two groups. Young women presented more frequently with stage III,T3/T4, Grade 3 tumors and HER-2 positive, Luminal B and triple negative subtypes. Women older than 40 years had more stage I, Luminal A and Grade 1/2 tumors. CONCLUSION: Brazilian women under the age of 40 have unfavorable clinicopathological features of BC at diagnosis with more aggressive subtypes and advanced stage compared with older women. No differences in socioeconomic and ethnical aspects were found but a higher percentage of young women had symptomatic detection of BC which could explain the later stage of disease at diagnosis. Young women were economically active and the majority married which highlights the socioeconomic impact of this disease in Brazil.

Breast cancer features by age groups at diagnosis in Brazilian women.InformationGroup 1 (≤40 years)Group 2 (&gt; 40 years)p-valueN: 2888486 (16.83%)2402 (83.17%) Stage at diagnosis  p&lt; 0.001I76 (19.2%)541 (27.8%) II156 (39.4%)816 (41.9%) III146 (36.8%)489 (25.1%) IV19 (4.6%)101 (5.2%) Tumor size  p&lt; 0.001T1114 (27.1%)749 (36.9%) T2141 (33.6%)764 (37.6%) T3101 (24.1%)282 (13.9%) T464 (15.2%)235 (11.6%) Tumor grade  p &lt; 0.001Grade 146 (10.7%)381 (17.9%) Grade 2198 (46.2%)1150 (52.0%) Grade 3185 (43.1%)641 (30.1%) Molecular Subtype  p &lt; 0.001Luminal A106 (30.6%)957 (51.3%) Luminal B - HER 2 negative55 (15.8%)212 (11.4%) Luminal B- HER 2 positive79 (22.8%)298 (16.0%) HER 2 positive27 (7.8%)135 (7.2%) Triple negative80 (23.0%)264 (14.1%) 

Citation Format: Franzoi MA, Rosa D, Barrios C, Bines J, Cronemberger E, Queiroz G, Cordeiro de Lima VC, Junior R, Couto J, Emerenciano K, Resende H, Crocamo S, Reinert T, Van Evyl B, Neron Y, Dybal V, Lazaretti N, Costamilan RdC, de Andrade D, Mathias C, Zerwes Vacaro G, Borges G, Silva K, Werutsky G, Morelle A, Sampaio Filho CA, Mano M, Zaffaroni F, Simon S, Liedke PE. Advanced stage at diagnosis and worse clinicopathologic features in young woman with breast cancer. A sub-analysis of Brazilian population through the AMAZONA III study (GBECAM 0115) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-08-27.

Abstract P1-08-29: Current status of clinical and pathological characteristics of breast cancer patients in Brazil: Results of the AMAZONA III study (GBECAM 0115)

BACKGROUND

Breast cancer (BC) is the most common tumor in women in Brazil with about 60 thousand new cases estimated per year. In low and middle-income countries, patients with BC are diagnosed with more advanced stages as compared with high-income countries. In Brazil, disparities in access to new therapies are recognized; previous data suggests worse survival of BC patients treated in the public system. The aim of AMAZONA III study (GBECAM 0115) is to describe the current status of BC care in Brazil. Here we report patients data at baseline.

METHODS

The AMAZONA III is a prospective BC registry that included women 18 years or older with newly diagnosed stage I to IV BC from 22 sites in Brazil in the period of January 2016 to March 2018. All patients provided written informed consent; data was collected from interview and medical charts, comprising clinical-demographic variables, initial treatment and a planned follow-up for 5 years. BC subtypes were defined by hormone receptor (HR) expression, HER2 status and grade according to von Minckwitz G. et al 2012. Here we present a descriptive analysis of the patients' baseline characteristics. Continuous variables are shown as mean (standard-deviation) and categorical variables by its absolute and relative frequencies. The study is registered in clinicaltrials.gov NCT02663973.

RESULTS

A total of 2950 patients were included in the study. Median age at diagnosis was 53 years old (8.4% &lt;= 35 years, 34.8% 36-50 years, 56.8% &gt; 50 years), 58.6% were white, 34.4% had brown skin-color, 83% had children before BC diagnosis (median of 1 child/patient) and 63.1% had public health insurance. In terms of method of detection 34% were screen-detected whereas 66% were symptomatic, the last was even higher (70%) in patients in younger than 50 years. The distribution of BC stage at diagnosis was I (26.4%), II (41.6%), III (27%) and IV (5%). The most common histologies were ductal (80.9%) and lobular carcinoma (6.9%). The pathological characteristics were HR positive in 78.0%, HER-2 positive in 23.4% and grade 2 in 51%. BC subtypes were as follows: Luminal A 48%, Luminal B 12%, Luminal HER2 positive 17%, Non-luminal HER2 positive 7.3% and Triple negative 15.5%.

DISCUSSION

Breast cancer is diagnosed at an earlier age among Brazilian patients. The majority of patients were detected through symptomatic BC and therefore a significant proportion is still diagnosed in stages III and IV. Among other factors, these findings could have a significant impact in treatment outcomes. Further analysis of this large cohort of patients will help to identify other important elements and direct future strategies for breast cancer control.

TRIAL REGISTRY: NCT02663973

KEYWORDS: Breast Cancer; Epidemiology; Treatment; Brazil

Citation Format: Rosa D, Barrios C, Bines J, Werustky G, Cronemberger E, Queiroz GS, Lima VC, Freitas-Júnior R, Couto J, Emerenciano K, Resende H, Crocamo S, Reinert T, Van Eyil B, Néron Y, Dybal V, Lazaretti N, Costamilan RC, Andrade DA, Mathias C, Vacaro GZ, Borges G, Torres KL, Morelle A, Sampaio Filho CA, Mano M, Zaffaroni F, Simon S. Current status of clinical and pathological characteristics of breast cancer patients in Brazil: Results of the AMAZONA III study (GBECAM 0115) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-08-29.

139 Effect of protein and calcium ionophore A23187 concentration on hyperactivated motility and acrosome status of stallion sperm

In vitro fertilization does not occur readily in the horse. Fertilization can be achieved using sperm treated with the calcium ionophore A23187 (CaI), but rates are low and variable. In order to fertilize, it is thought that the sperm must show hyperactivated motility and undergo the acrosome reaction. The presence of protein in the media is thought to suppress the effect of CaI, but protein is needed for maintenance of sperm motility. Therefore, the objective of this study was to assess the effect of CaI in the presence or absence of protein on the acrosome and on hyperactivated motility of equine sperm. For this purpose, sperm from 4 stallions were exposed for 10min at 37°C to vehicle or to 1 (C1), 5 (C5) or 10 (C10) μM CaI, with (BSA) or without (N) 7mg mL−1 BSA. The sperm were then washed and incubated at 37°C for 2h. Total and hyperactivated motility were measured by computer-assisted semen analysis. Sperm were considered hyperactivated if curvilinear velocity was &gt;180μm s−1, amplitude of lateral head displacement was &gt;12μm, linearity was &lt;30% and fractal dimension value was &gt;1.3. The percentage of live acrosome-reacted sperm was measured by flow cytometry after staining with propidium iodide and Pisum sativum agglutinin. Data were analysed by repeated-measures 2-way ANOVA. Results were expressed as mean±standard error. Total motility in C5 and C10 treatments was significantly decreased in relation to control (BSA-vehicle) starting at 30min of incubation (35.42±13.57 to 28.20±13.10% v. 71.72±9.21%, respectively; P&lt;0.05). Hyperactivated motility was significantly lower in C10, C5 and N-C1 than in control after 2h of incubation (1.46±0.64v. 3.10±0.58%, respectively). Live acrosome-reacted sperm were significantly higher (P&lt;0.05) for BSA-C5 (14.04±1.99%) and BSA-C10 (14.85±2.52%) than for control (7.50±1.62%) after 2h of incubation. The exposure to sperm of concentrations ≥5μM CaI was associated with loss of motility from 30min of incubation on. However, 2h of incubation after ≥5 μM CaI in the presence of BSA were needed to increase the percentage of live acrosome-reacted sperm. This mismatch between motility and acrosome response helps to clarify the reasons for the variable effect of sperm CaI treatment on equine IVF. Further studies measuring calcium influx and assessing the effect of sperm pre-incubation on CaI response are needed to explore mechanisms for equine in vitro sperm capacitation.