12104 Background: Chemotherapy induced nausea and vomiting (CINV) is a highly prevalent adverse event1,2 that can result in decreased quality of life, dose reduction and interruptions of treatment.3 Four drug protocol including Olanzapine, 5-hydroxytryptamine type 3 receptor (5HT3) antagonist, a neurokinin 1 receptor (NK1) antagonist and dexamethasone is the current standard of care for highly emetogenic chemotherapy (HEC) 2,4-6. Corticosteroids are associated with side effects like insomnia and weight gain. To our knowledge, total Dexamethasone omission has not been addressed previously. Methods: This is a prospective single arm phase II study designed to evaluate the efficacy of Olanzapine, Netupitant and Palonosetron in controlling nausea and vomiting induced by highly emetogenic chemotherapy. Eligible patients were women with histologic confirmed breast cancer, planned to start treatment with Doxorubicin and Cyclophosphamide. Exclusion criteria included use of opioids or antipsychotic medications, medical condition that could potentially cause vomiting or inability to take oral medications. Patients were assigned to take Olanzapine 5mg QD, days 1 – 5, Netupitant 300mg and Palonosetron 0.5mg on day one. No corticosteroid use was allowed. The null hypothesis considered that the scheme containing Olanzapine, Netupitant and Palonosetron could not effectively control nausea. Based on a previous phase III study with Olanzapine (Navari et al.), we set the control of nausea at 20% and the expected control rate at 40% for the present study. To reach 5% (two-sided) significance and 80% statistical power, we calculated that a minimum sample size of 50 patients was required, assuming a 5% dropout rate. We used the one-sample T-test of proportion to analyze the data, based on intent-to-treat (ITT) The primary endpoint was complete control of nausea in the first 5 days after chemotherapy administration. Secondary endpoints were complete emesis control (no emesis, no use of rescue medication) and complete control (no emesis, no rescue and no nausea) Results: Fifty patients were enrolled from January 2020 to December 2021. The median age was 47.6 years-old (range: 29 – 78 years) and 48 patients (96%) received chemotherapy with curative intent. For the primary endpoint, complete nausea control rate was 46% (IC 32 – 59%) and p < 0.0001. The emesis control rate was 68% (IC 55 – 80%) and overall control rate was 46% (IC 32 – 59%). One patient dropped out for dizziness and drowsiness following administration of Olanzapine. Conclusions: Omitting Dexamethasone for highly emetogenic chemotherapy is feasible and showed similar control of nausea and vomiting compared to standard four-drug protocol. This could be a potential prophylactic regimen of choice for patients who have a contraindication for Dexamethasone use. Clinical trial information: NCT04669132.

e12559 Background: Pathologic Complete Response (pCR) to neoadjuvant chemotherapy (NAC) in breast cancer is strongly associated with a favorable prognosis. We evaluated whether there is a correlation between serum levels of circulating tumor DNA (ctDNA) during neoadjuvant therapy with obtaining pCR and detection of residual disease after treatment. Methods: ctDNA was isolated from 310 plasma samples of 27 patients diagnosed with localized and/or locally advanced breast cancer treated with standard NAC alone or combined with immunotherapy and/or anti-HER 2- targeted therapy when indicated. Blood was collected at pretreatment, every 15 days during treatment and before surgery. Results: Eight (29%) of the 27 patients presented pCR, 4 triple negative (50%, 3 HER2+ (37%) and 1 (13%) luminal B. We observed that throughout the neoadjuvant treatment in the seventh collection the ctDNA levels were significantly higher in patients who did not presented pCR in relation to those who achieved it, p-value = 0.014. 62% of patients who presented pCR in the surgical specimen also had a complete radiological response, with a significant correlation, p-value = 0.02492. Although we did not find statistical significance, we did note that patients who presented pCR had a tendency towards an initial increase in their ctDNA levels after the first cycle of chemotherapy. Conclusions: ctDNA dosage in the third month (seventh collection) of neoadjuvant treatment is inversely correlated with the achievement of tumor pCR. The tendency we saw of an increased ctDNA levels soon after the initiation neoadjuvant chemotherapy could indicate tumor sensitivity by the increase in cell death with release of ctDNA into the circulation. Clinical trial information: NCT05050890.

e24112 Background: Anticipatory nausea (AN) and vomiting are unpleasant symptoms observed in anticipation of chemotherapy regimens. It is best described as a learned response through classical conditioning when one or more distinctive features of the chemotherapy clinic (conditioned stimuli) associated with the administration of emetogenic chemotherapy (unconditioned stimuli) trigger the emetogenic reflex. Little is known about AN's occurrence after the advent of the new neurokinin-1 antagonist. This prospective study evaluated AN's prevalence in ambulatory breast cancer patients receiving high effective antiemetic prophylaxis and evaluated potential predictors of AN. Methods: This prospective observational study was performed at a single Brazilian Institution. Key inclusion criteria were patients aged 18 years or older with breast cancer scheduled to receive anthracycline chemotherapy with an appropriate antiemetic regimen, including a neurokinin-1 receptor antagonist, a serotonin-3 receptor antagonist, and a corticosteroid. Eligible patients used a diary to record nausea, vomiting, and use of rescue medication in the first 2-cycle of treatment through 120 after infusion. AN was assessed before chemotherapy on day 1 of cycle two. We excluded patients with nausea and vomiting presented 24h before cycle one and patients who did not receive standard antiemetic prophylaxis. Results: Between August 04, 2020, and August 12, 2021, 60 patients were screened, and 52 patients were enrolled. The mean age was 50,8 (28 – 69), the majority had stage III (53,8%) and received chemotherapy with curative intent (94%). During cycle 1, the frequency of overall nausea and vomiting was 67.31%, and severe nausea and vomiting (defined as grade > 4 at a 10-point visual scale or use of rescue medication) was 55.77%. Ten patients had AN (19.23%). The occurrence of nausea and vomiting during cycle one was the only statistically significant predictor of AN (OR = 16, 95% CI 2.4, 670.9, p-value = 0.0003). Conclusions: The prevalence of AN is still high in the era of neurokinin-1 antagonists, and failure of antiemetic control on cycle one remains the main risk factor. All efforts should be made to control chemotherapy-induced nausea or nausea and vomiting on cycle one to avoid AN. Clinical trial information: NCT04785495.