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Supplementary Table from Lenalidomide plus R-GDP (R2-GDP) in Relapsed/Refractory Diffuse Large B-Cell Lymphoma: Final Results of the R2-GDP-GOTEL Trial and Immune Biomarker Subanalysis

Purpose:New therapeutic options are needed in relapsed/refractory diffuse large B-cell lymphoma (R/R DLBCL). Lenalidomide-based schedules can reverse rituximab refractoriness in lymphoma.Patients and Methods:In the phase II R2-GDP trial, 78 patients unsuitable for autologous stem cell transplant received treatment with the following schedule: lenalidomide 10 mg Days (D)1–14, rituximab 375 mg/m2 D1, cisplatin 60 mg/m2 D1, gemcitabine 750 mg/m2 D1 and D8, and dexamethasone 20 mg D1–3, up to 6 cycles (induction phase), followed by lenalidomide 10 mg (or last lenalidomide dose received) D1–21 every 28 days (maintenance phase). Primary endpoint was overall response rate (ORR). Secondary endpoints included progression-free survival (PFS), overall survival (OS), safety, and monitorization of key circulating immune biomarkers (EU Clinical Trials Register number: EudraCT 2014-001620-29).Results:After a median follow-up of 37 months, ORR was 60.2% [37.1% complete responses (CR) and 23.1% partial responses (PR)]. Median OS was 12 months (47 vs. 6 months in CR vs. no CR); median PFS was 9 months (34 vs. 5 months in CR vs. no CR). In the primary refractory population, ORR was 45.5% (21.2% CR and 24.3% PR). Most common grade 3–4 adverse events were thrombocytopenia (60.2%), neutropenia (60.2%), anemia (26.9%), infections (15.3%), and febrile neutropenia (14.1%). Complete responses were associated with a sharp decrease in circulating myeloid-derived suppressor cells and regulatory T cells.Conclusions:R2-GDP schedule is feasible and highly active in R/R DLBCL, including the primary refractory population. Immune biomarkers showed differences in responders versus progressors.

Supplementary Data from Lenalidomide plus R-GDP (R2-GDP) in Relapsed/Refractory Diffuse Large B-Cell Lymphoma: Final Results of the R2-GDP-GOTEL Trial and Immune Biomarker Subanalysis

Background We evaluated a new chemoimmunotherapy combination based on the anti-PD1 monoclonal antibody pembrolizumab and the pyrimidine antimetabolite gemcitabine in HER2- advanced breast cancer (ABC) patients previously treated in the advanced setting, in order to explore a potential synergism that could eventually obtain long term benefit in these patients. Methods HER2-negative ABC patients received 21-day cycles of pembrolizumab 200 mg (day 1) and gemcitabine (days 1 and 8). A run-in-phase (6 + 6 design) was planned with two dose levels (DL) of gemcitabine (1,250 mg/m2 [DL0]; 1,000 mg/m2 [DL1]) to determine the recommended phase II dose (RP2D). The primary objective was objective response rate (ORR). Tumor infiltrating lymphocytes (TILs) density and PD-L1 expression in tumors and myeloid-derived suppressor cells (MDSCs) levels in peripheral blood were analyzed. Results Fourteen patients were treated with DL0, resulting in RP2D. Thirty-six patients were evaluated during the first stage of Simon’s design. Recruitment was stopped as statistical assumptions were not met. The median age was 52; 21 (58%) patients had triple-negative disease, 28 (78%) visceral involvement, and 27 (75%) ≥ 2 metastatic locations. Progression disease was observed in 29 patients. ORR was 15% (95% CI, 5–32). Eight patients were treated ≥ 6 months before progression. Fourteen patients reported grade ≥ 3 treatment-related adverse events. Due to the small sample size, we did not find any clear association between immune tumor biomarkers and treatment efficacy that could identify a subgroup with higher probability of response or better survival. However, patients that experienced a clinical benefit showed decreased MDSCs levels in peripheral blood along the treatment. Conclusion Pembrolizumab 200 mg and gemcitabine 1,250 mg/m2 were considered as RP2D. The objective of ORR was not met; however, 22% patients were on treatment for ≥ 6 months. ABC patients that could benefit of chemoimmunotherapy strategies must be carefully selected by robust and validated biomarkers. In our heavily pretreated population, TILs, PD-L1 expression and MDSCs levels could not identify a subgroup of patients for whom the combination of gemcitabine and pembrolizumab would induce long term benefit. Trial registration ClinicalTrials.gov and EudraCT (NCT03025880 and 2016–001,779-54, respectively). Registration dates: 20/01/2017 and 18/11/2016, respectively.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection may produce a systemic disease, the coronavirus disease-19 (COVID-19), with high morbidity and mortality. Even though we do not fully understand the interaction of innate and adaptive immunity in the control and complications of the viral infection, it is well recognized that SARS-CoV-2 induces an immunodepression that impairs the elimination of the virus and favors its rapid dissemination in the organism. Even less is known the possible participation of inhibitory cells of the innate immune system, such as the myeloid-derived suppressor cells (MDSCs), or the adaptive immune system, such as the T regulatory cells (Tregs). That is why we aimed to study blood levels of MDSCs as well as lymphocyte subpopulations including Tregs, and activated (OX-40+) and inhibited (PD-1) T lymphocytes in patients with COVID-19 in comparison with data obtained from control donors. We have found that 12 hospitalized patients with COVID-19 and no health history of immnosuppression had a significant increase in the number of peripheral monocytic MDSCs, but not Tregs, as well as an increase in the number of inhibited or exhausted T cells, whereas the number of activated T cells was significantly decreased compared with that from 20 healthy controls. Moreover, there was a significant negative correlation (- 0.791) between the number of M-MDSC and the number of activated T cells. Therefore, SARS-Cov-2 seems to recruit MDSCs, and these inhibitory cells may contribute to the immunosuppression observed in patients with COVID-19.

Lymphoma is a neoplasm arising from B or T lymphocytes or natural killer cells characterized by clonal lymphoproliferation. This tumor comprises a diverse and heterogeneous group of malignancies with distinct clinical, histopathological, and molecular characteristics. Despite advances in lymphoma treatment, clinical outcomes of patients with relapsed or refractory disease remain poor. Thus, a deeper understanding of molecular pathogenesis and tumor progression of lymphoma is required. Epigenetic alterations contribute to cancer initiation, progression, and drug resistance. In fact, over the past decade, dysregulation of epigenetic mechanisms has been identified in lymphomas, and the knowledge of the epigenetic aberrations has led to the emergence of the promising epigenetic therapy field in lymphoma tumors. However, epigenetic aberrations in lymphoma not only have been found in tumor cells, but also in cells from the tumor microenvironment, such as immune cells. Whereas the epigenetic dysregulation in lymphoma cells is being intensively investigated, there are limited studies regarding the epigenetic mechanisms that affect the functions of immune cells from the tumor microenvironment in lymphoma. Therefore, this review tries to provide a general overview of epigenetic alterations that affect both lymphoma cells and infiltrating immune cells within the tumor, as well as the epigenetic cross-talk between them.

Purpose: New therapeutic options are needed in relapsed/refractory diffuse large B-cell lymphoma (R/R DLBCL). Lenalidomide-based schedules can reverse rituximab refractoriness in lymphoma. Patients and Methods: In the phase II R2-GDP trial, 78 patients unsuitable for autologous stem cell transplant received treatment with the following schedule: lenalidomide 10 mg Days (D)1–14, rituximab 375 mg/m2 D1, cisplatin 60 mg/m2 D1, gemcitabine 750 mg/m2 D1 and D8, and dexamethasone 20 mg D1–3, up to 6 cycles (induction phase), followed by lenalidomide 10 mg (or last lenalidomide dose received) D1–21 every 28 days (maintenance phase). Primary endpoint was overall response rate (ORR). Secondary endpoints included progression-free survival (PFS), overall survival (OS), safety, and monitorization of key circulating immune biomarkers (EU Clinical Trials Register number: EudraCT 2014-001620-29). Results: After a median follow-up of 37 months, ORR was 60.2% [37.1% complete responses (CR) and 23.1% partial responses (PR)]. Median OS was 12 months (47 vs. 6 months in CR vs. no CR); median PFS was 9 months (34 vs. 5 months in CR vs. no CR). In the primary refractory population, ORR was 45.5% (21.2% CR and 24.3% PR). Most common grade 3–4 adverse events were thrombocytopenia (60.2%), neutropenia (60.2%), anemia (26.9%), infections (15.3%), and febrile neutropenia (14.1%). Complete responses were associated with a sharp decrease in circulating myeloid-derived suppressor cells and regulatory T cells. Conclusions: R2-GDP schedule is feasible and highly active in R/R DLBCL, including the primary refractory population. Immune biomarkers showed differences in responders versus progressors.

Currently, the standard of care for luminal metastatic breast cancer is the combination of cyclin inhibitors with hormone therapy. Palbociclib and Ribociclib have been approved for marketing since 2017 and Abemaciclib since 2019 in Spain. In our center we have experience with the three cdk 4/6 inhibitors in different lines of treatment and patient profiles. We gather in the present work the unicentric experience with the three icdk 4/6. We have collected a total of 152 patients treated with the different cyclin inhibitors, achieving median PFS of 32.1 months for Palbociclib, 28.6 months for Ribociclib and 18.4 months for Abemaciclib. Overall survival data is still immature. The context of the patient and the disease has a significant impact on the results, as well as the line of treatment used. The toxicity profile of the three drugs does not differ from what the registry trials describe, with neutropenia being the most common side effect. We also describe dose reductions produced by the three icdk4/6. Conclusions: This is a real-life study with experience in a single center with the three icdk4/6 currently marketed with a cohort of more than 150 patients. We present data that conform to what was reported by the clinical trials PALOMA, MONALEESA and MONARCH. The data will be updated on the date of the congress for its presentation. Citation Format: Fernando Henao, Esteban Nogales Fernández, Lourdes Sevilla Ortega, Ruben De Toro Salas, Natalia Palazón Carrión, Maria del Carmen Álamo de la Gala, Alberto Sanchez-Camacho Mejías, Maria Luisa Sanchez Leon, Luis de la Cruz-Merino. Unicentric experience with icdk4/6 in metastatic breast cancer [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 P3-01-01.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection may produce a systemic disease, the coronavirus disease-19 (COVID-19), with high morbidity and mortality. Even though we do not fully understand the interaction of innate and adaptive immunity in the control and complications of the viral infection, it is well recognized that SARS-CoV-2 induces an immunodepression that impairs the elimination of the virus and favors its rapid dissemination in the organism. Even less is known about the possible participation of inhibitory cells of the innate immune system, such as the myeloid-derived suppressor cells (MDSCs), or the adaptive immune system, such as the T regulatory cells (Tregs). That is why we aimed to study blood levels of MDSCs, as well as lymphocyte subpopulations, including Tregs, and activated (OX-40+) and inhibited (PD-1) T lymphocytes in patients with mild COVID-19 in comparison with data obtained from control donors. We have found that 20 hospitalized patients with COVID-19 and no health history of immunosuppression had a significant increase in the number of peripheral monocytic MDSCs (M-MDSC), but a decrease in Tregs, as well as an increase in the number of inhibited or exhausted T cells, whereas the number of activated T cells was significantly decreased compared with that from 20 healthy controls. Moreover, there was a significant negative correlation (r = 0.496) between the number of M-MDSC and the number of activated T cells. Therefore, M-MDSC rather than Tregs may contribute to the immunosuppression observed in patients with COVID-19., S.-M. received support from Junta de Andalucia and University of Seville (PAIDI CTS-151 group), A.P. and J.R.-B. receive support for research from Plan Nacional de I+D+i 2013–2016 and Instituto de Salud Carlos III, Subdirección General de Redes y Centros de Investigación Cooperativa, Ministerio de Ciencia, Innovación y Universidades, Spanish Network for Research in Infectious Diseases (REIPI RD16/0016/0001), cofinanced by European Development Regional Fund “A way to achieve Europe,” Operative Program Intelligence Growth 2014–2020. LdC-M received support from the Asociación de Mujeres con Cáncer de Mama (AMAMA Sevilla), Fundación Sandra Ibarra, and Asociación de Cáncer de Mama de Brenes.

Simple Summary Melanoma still represents a major challenge for health systems around the world. A classical treatment for patients with a high tumor burden or rapidly recurrent in-transit metastases is isolated limb perfusion (ILP) therapy instead of locoregional surgical resection, or when the latter is no longer feasible. In this era of modern systemic treatments for melanoma, it still remains interesting to analyze the role of management approaches for locoregionally-advanced disease, such as isolated limb perfusion (ILP). With this purpose, we conducted a systematic review updating the available literature on ILP for malignant melanomas. The main objectives of this review were to focus on the effectiveness and safety of ILP. In conclusion, ILP, with its low incidence of regional and systemic toxicity, is a valuable palliative treatment not only for patients with disease confined to a limb, but also for patients with a metastatic melanoma with a bulky or symptomatic disease, in order to improve their quality of life. Abstract Background. Isolated limb perfusion (ILP) is a locoregional procedure indicated by the unresectable melanoma of the limbs. Its complexity and highly demanding multidisciplinary approach means that it is a technique only implemented in a few referral centers around the globe. This report aims to examine its potential role in the era of targeted therapies and immunotherapy by conducting a systematic review of the literature on ILP. Methods. PubMed, Embase and Cochrane Library were searched. The eligibility criteria included publications from 2000–2020 providing valid data o effectiveness, survival or toxicity. Studies in which the perfusion methodology was not clearly described, letters to the editor, non-systematic reviews and studies that applied outdated clinical guidelines were excluded. To rule out studies of a low methodological quality and assess the risk of bias, the following aspects were also required: a detailed description of the applied ILP regimen, the clinical context, follow-up periods, analyzed clinical endpoints, and the number of analyzed ILPs. The disagreements were resolved by consensus. The results are presented in tables and figures. Results. Twenty-seven studies including 2637 ILPs were selected. The median overall response rate was 85%, with a median complete response rate of 58.5%. The median overall survival was 38 months, with a 5-year overall survival of 35%. The toxicity was generally mild according to Wieberdink toxicity criteria. Discussion. ILP still offer a high efficacy in selected patients. The main limitation of our review is the heterogeneity and age of most of the articles, as well as the absence of clinical trials comparing ILP with other procedures, making it difficult to transfer its results to the current era. Conclusions. ILP is still an effective and safe procedure for selected patients with unresectable melanoma of the limbs. In the era of targeted therapies and immunotherapy, ILP remains an acceptable and reasonable palliative treatment alternative, especially to avoid limb amputations. The ongoing clinical trials combining systemic therapies and ILP will provide more valuable information in the future to clarify the potential synergism of both strategies.

The PANGEA-Breast trial evaluated a new chemo-immunotherapeutic combination that would synergistically induce long-term clinical benefit in HER2-negative advanced breast cancer patients. Treatment consisted of 21-day cycles of 200 mg of pembrolizumab (day 1) plus gemcitabine (days 1 and 8). The primary objective was the objective response rate (ORR). The tumor infiltrating lymphocytes (TILs) density and PD-L1 expression in tumor, and the myeloid-derived suppressor cells (MDSCs) level in peripheral blood, were analyzed to explore associations with treatment efficacy. Considering a two-stage Simon’s design, the study recruitment was stopped after its first stage as statistical assumptions were not met. A subset of 21 triple-negative breast cancer (TNBC) patients was enrolled. Their median age was 49 years, 15 patients had visceral involvement, and 16 had ≤3 metastatic locations. Treatment discontinuation due to progressive disease (PD) was reported in 16 patients. ORR was 15% (95% CI 3.2–37.9). Four patients were on treatment &gt, 6 months before PD. Grade ≥3 treatment-related adverse events were observed in 8 patients, where neutropenia was the most common. No association was found between TILs density, PD-L1 expression or MDSCs levels and treatment efficacy. ORR in TNBC patients also did not meet the assumptions, but 20% were on treatment &gt, 6 months.

The search of prognostic factors is a priority in diffuse large B-cell lymphoma (DLBCL) due to its aggressiveness. We have recently found that the level of circulating MDSCs is a good marker of survival in a translational study based on a trial (EudraCT Number: 2014-001620-29), using lenalidomide combined with R-GDP (rituximab plus gemcitabine, cisplatin, and dexamethasone). Since Vitamin D is a known immunomodulator, we have studied blood levels of these cell populations comparing patients with deficit of vitamin D levels (&lt, 15 ng/mL with those with normal levels &gt, 15 ng/mL. Mann–Whitney U test was used to compare cells distributions between groups, Wilcoxon test to compare cells distribution at different times and Spearman test to measure the association between cell populations. Patients with vitamin D deficit maintained the increased level of immune suppressor cells, whereas we observed a depletion of all immune suppressor cells in patients with normal vitamin D levels. In conclusion, we have confirmed the importance of vitamin D in the response to treatment in R/R DLBCL, suggesting that vitamin D deficit may be involved in the immune deficit of these patients, and thus, vitamin D supplementation in these patients may help to obtain a better response, warranting further investigation.

Background: Immune escape of tumor cells is a new hallmark of cancer in general, and breast cancer, in particular. Previous studies have demonstrated that the immunological profile in peripheral blood may be a prognostic and/or predictive biomarker in breast cancer. Thus, higher number of regulatory T cells (Tregs) in blood from patients with breast cancer has been reported in relation to normal donors. In the present study, we planned to evaluate the changes in different cell populations in peripheral blood: neutrophils, monocytes and lymphocytes, as well as lymphocyte subpopulations [natural killer (NK), B lymphocytes, T lymphocytes, both CD4(+) and CD8(+), and Tregs] from patients with local breast cancer (both Her2(+) and Her2(-)), before, during and after neoadjuvant chemotherapy.Methods: We have employed flow cytometry for the cell analysis of fresh samples obtained before and whilst the neoadjuvant treatment was accomplished. We have studied 50 successive patients from the Breast Cancer Unit of the Virgen Macarena University Hospital during 2 years.Results: Neoadjuvant chemotherapy induced a significant reduction in B cells, especially in Her2(-) patients, and a reduction in NK cells. CD4(+) T cells decreased, whereas CD8(+) cells only decreased in Her2(-) patients. Tregs were also diminished, especially in Her2(+) patients, in response to treatment. Thus, higher CD8/Treg ratio was observed in Her2(+) patients. A higher percentage of Her2(+) patients (66.6%) achieved complete response than Her2(-) patients (27.5%). Monocytes and neutrophils were not changed in peripheral blood.Conclusions: Even though the decrease in B cells and NK cells in response to chemotherapy may be deleterious in the neoadjuvant treatment of breast cancer, the decrease in Tregs and CD4 T cells, but not CD8 T cells, increasing the CD8/Treg ratio, especially in Her2(+) patients, may reveal a new tool to monitor the immune response in breast cancer treated with chemotherapy in the neoadjuvant setting.

Identification of the different elements intervening at the immunoedition process, in each body compartment, seems key to explain clinical evolution in several tumor types. In this study, a set of immune biomarkers (myeloid derived suppressor cells, regulatory T cells, and OX40+ and PD-1+ T lymphocytes counts) in peripheral blood of patients diagnosed with advanced breast cancer, were analyzed prior to and along the implementation of first line antineoplastic therapy. Subsequently, a formal comparison between groups with clinical benefit versus progression of disease and with a healthy women cohort was executed. Results reflected that patients basally showed higher levels of myeloid derived suppressor cells (35.43, IR=180.73 vs 17.53, IR=16.96 cells/μl; p=0.001) and regulatory T cells (32.05, IR=29.84 vs 22.61, IR=13.57 cells/μl; p=0.001) in comparison with healthy women. Furthermore, after therapy, an increase in the number of activated T lymphocytes (expressing OX40), and a decrease of immune inhibitory cells (MDSCs, and Tregs), and the number of inhibited (or exhausted) T lymphocytes (expressing PD-1), could be ascertained in patients with clinical benefit (p≤0.001). The opposite trend was observed in the case of disease progression. These findings suggest that some critical immune elements can be easily detected and measured in peripheral blood, which open a new opportunity for translational research, as they seem to be clearly correlated with clinical evolution, at least in ABC.

Introduction: Leptomeningeal dissemination due to HER2-overexpressing breast cancer is a rare and hard to treat complication with short-term dismal prognosis. Patient concerns: A 34-year-old female previously treated because of HER2+ breast cancer is admitted to the Neurology Department in December 2016 due to sensory-motor neurological semiology. Diagnosis: A wide set of diagnostic tests is performed and finally cytologic findings after repeated CSF confirm leptomeningeal infiltration by breast carcinoma (panCK+, GATA3+). Interventions: Weekly intrathecal triple therapy with methotrexate, cytarabine and hydrocortisone plus trastuzumab is carried out during 4 months. Outcomes: Clinical and pathological response that lasts more than 24 months. Conclusion: Leptomeningeal carcinomatosis is an oncological situation where conventional therapies have limited activity. In HER2+ advanced breast cancer patients, intrathecal therapy with anti-HER2 therapy (trastuzumab) is feasible and may reach long-term disease control, especially in cases of low-tumor burden.

Immunology and immunotherapy of cancer is an expanding field in oncology, with recent great achievements obtained through the new successful approaches implemented to circumvent immune evasion, which is undoubtedly considered a novel hallmark of cancer. Translational research in this topic has revealed targets that can be modulated in the clinical setting with new compounds and strategies. Like most of the tumors, breast cancer is considered a complex and heterogeneous disease in which host immune responses have been also recently demonstrated of critical relevance. T infiltrating lymphocyte measurement is suggested as a powerful new tool necessary to predict early breast cancer evolution, especially for the her2-positive and triple-negative subtypes. Other biomarkers in tissue and peripheral blood are under intense scrutiny to ascertain their eventual role as prognostic and/or predictive factors. This background has fueled the interest in developing clinical research strategies to test activity of modern immunotherapy in breast cancer, which constitutes the main focus of this review.

8019 Background: Lenalidomide is an immunomodulatory drug that could reverse rituximab refractoriness in lymphoma patients (pts). We conducted an open label multicenter phase 2 trial testing the efficacy and toxicity of a combination of lenalidomide and rituximab (R2) plus GDP schedule (R2-GDP) in Relapsed/Refractory Diffuse Large B Cell Lymphoma (R/R DLBCL) pts, not suitable for autologous stem cell transplant (ASCT). Methods: Patients with R/R DLBCL previously treated with at least 1 prior line of immunochemotherapy including rituximab, and not candidates for ASCT, were eligible. After a run-in phase period, treatment consisted of an induction phase with lenalidomide (LEN) 10 mg po d1-14, rituximab 375 mg/m2 iv d1, cisplatin 60 mg/m2 iv d1, gemcitabine 750 mg/m2 iv d1 and d8 and dexamethasone 20 mg d1-3, up to a maximum of 6 cycles. Pts without disease progression (DP) entered into a maintenance phase with LEN 10 mg, or last LEN dose received in the induction phase, d1-21 in cycles every 28 days. Primary endpoint was overall response rate (ORR) by investigator assessment. Secondary endpoints included disease free survival (DFS), event free survival (EFS), overall survival (OS), safety and response by cell of origin (COO), type of DLBCL (double-triple hit) and other microenvironment and genomic biomarkers. Results: 79 pts were enrolled between April 2015 and September 2018. Median age was 70 years (range 23-86), 48,7% women. 78 pts were considered for efficacy and safety in the intention to treat (ITT) analysis. With a median follow-up of 13 months at the time of cut-off (November 2019), ORRwas 59.0%, with 32.1% complete responses (CR) and 26.9% partial responses (PR). In the primary refractory population (n = 33), ORR was 45.5%, with 21.2% CR and 24.3% PR. There were no statistically significant differences in ORR with respect to COO. In Double-Hit R/R DLBCL (n = 16), ORR was 37.5% with 25% CR. Median OS was 12.0 months (6.9-17.0). Most common grade 3/4 (G3/4) adverse events were thrombocytopenia (60.2%), neutropenia (60.2%) and anemia (26.9%). Febrile neutropenia occurred in 14.1% pts. Most frequent non-hematologic G3/4 events were asthenia (19.2%), infection (15.3%) and renal insufficiency (6.4%). There were 4 toxic deaths related to the R2-GDP schedule. Conclusions: LEN with Rituximab and GDP (R2-GDP) is feasible and active in R/R DLBCL. Results in the primary refractory DLBCL population are particularly promising. Analysis of COO did not revealed differences in response rates. Immune biomarkers results will be showed at the meeting. Clinical trial information: EudraCT 2014-001620-29 .

2543 Background: High levels of myeloid-derived suppressor cells (MDSCs) seem a negative prognostic factor in advanced breast cancer (ABC) patients (pts). Preclinical studies suggest an immunomodulatory effect of some classical anti-tumor agents through alteration of MDSCs homeostasis. We analyzed the association of MDSCs and clinical evolution of ABC pts, taking into account the systemic treatment (tx) modulation of MDSCs levels in pts from two studies (“A”: GEICAM/2015-04 PANGEA-BREAST, NCT03025880 “Efficacy and Safety of Pembrolizumab and Gemcitabine in HER2-negative ABC”, and “B”: PI-0502-2014 “Peripheral blood analyses of immune response induced by 1st line tx of ABC according to clinical guidelines”). Methods: MDSCs (CD33+ CD11b+) levels were determined by flow-cytometry in peripheral blood samples at three time points (basal, at cycles 3 and 6) from: 39 HER2-negative heavily pretreated pts from study “A”, 43 non-pretreated pts (all subtypes) from study “B” and 20 women from a healthy cohort (HC), with no cancer diagnosis. MDSCs levels from the different cohorts were compared and correlated with pts with Clinical Benefit (CB: partial/complete response + disease stabilization) vs pts with Progressive Disease (PD). Results: Tx response was assessed in 33 pts (85%) from study “A” and 39 pts (91%) from study “B”. CB was observed in 11 pts (28%) from study “A” and in 34 (79%) from study “B” while PD was observed in 22 pts (56%) from study “A” and in 5 (12%) from study “B”. Basal MDSCs levels were significantly higher in ABC pts (studies “A”+”B”) than in HC (15.95 vs 0.81 cells/µl, p = 0.009). At cycle 6, MDSCs were considerably lower in pts with CB vs DP (2.90 vs 13.75 cells/µl, p < 0.001). This decrease was more pronounced in study “B” than in study “A” pts (p < 0.001 vs p = 0.074, respectively), probably due to differences in number of events, tumor subtypes and tx between both studies. Conclusions: Our results suggest that ABC pts show alterations in MDSCs and that their decrease along tx may have a positive predictive value, highlighting the importance that immune-competent status may play in the evolution of ABC. MDSCs may represent a target for therapeutic purposes in ABC.