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Mast cells are unique tissue-resident immune cells of the myeloid lineage that have long been implicated in the pathogenesis of allergic and autoimmune disorders. More recently, mast cells have been recognized as key orchestrators of anti-tumor immunity, modulators of the cancer stroma, and have also been implicated in cancer cell intrinsic properties. As such, mast cells are an underrecognized but very promising target for cancer immunotherapy. In this review, we discuss the role of mast cells in shaping cancer and its microenvironment, the interaction between mast cells and cancer therapies, and strategies to target mast cells to improve cancer outcomes. Specifically, we address (1) decreasing cell numbers through c-KIT inhibition, (2) modulating mast cell activation and phenotype (through mast cell stabilizers, FcεR1 signaling pathway activators/inhibitors, antibodies targeting inhibitory receptors and ligands, toll like receptor agonists), and (3) altering secreted mast cell mediators and their downstream effects. Finally, we discuss the importance of translational research using patient samples to advance the field of mast cell targeting to optimally improve patient outcomes. As we aim to expand the successes of existing cancer immunotherapies, focused clinical and translational studies targeting mast cells in different cancer contexts are now warranted.

In the phase II NIMBUS trial, patients with human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (MBC) and high tumor mutational burden (TMB ≥ 9 mut/Mb) received nivolumab (3 mg/kg biweekly) and low-dose ipilimumab (1 mg/kg every 6 weeks) for 2 years or until progression. The primary endpoint was objective response rate (ORR) per RECIST 1.1 criteria. Among 30 patients enrolled, the median TMB was 10.9 mut/Mb (range: 9–110) and the confirmed objective response rate was 20%. Secondary endpoints included progression-free survival, overall survival, clinical benefit rate, and safety and tolerability, including immune-related adverse events (irAEs). A prespecified correlative outcome was to evaluate the ORR in patients with a TMB ≥ 14 mut/Mb. Patients with TMB ≥ 14 mut/Mb (n = 6) experienced higher response rates (60% vs 12%; p = 0.041) and showed a trend towards improved progression-free survival and overall survival compared to patients with TMB < 14 mut/Mb. Exploratory genomic analyses suggested that ESR1 and PTEN mutations may be associated with poor response, while clinical benefit was associated with a decrease or no change in tumor fraction by serial circulating tumor DNA during treatment. Stool microbiome analysis revealed that baseline blood TMB, PD-L1 positivity, and immune-related diarrhea are associated with distinct taxonomic profiles. In summary, some patients with hypermutated HER2-negative MBC experience extended clinical benefit with a dual immunotherapy regimen; a higher TMB, and additional genomic and microbiome biomarkers may optimize patient selection for therapy with nivolumab plus low-dose ipilimumab. (Funded by Bristol Myers Squibb; ClinicalTrials.gov identifier, NCT03789110). The current use of immune checkpoint inhibitors without chemotherapy on patients with metastatic breast cancer (MBC) has not proven useful. Here this group reports a phase 2 NIMBUS trial evaluating the efficacy/safety of nivolumab + low dose ipilimumab in 30 patients with hypermutated HER2-negative MBC.

Immune checkpoint inhibitors (ICIs) have improved overall survival for cancer patients, however, optimal duration of ICI therapy has yet to be defined. Given ICIs were first used to treat patients with metastatic melanoma, a condition that at the time was incurable, little attention was initially paid to how much therapy would be needed for a durable response. As the early immunotherapy trials have matured past 10 years, a significant per cent of patients have demonstrated durable responses; it is now time to determine whether patients have been overtreated, and if durable remissions can still be achieved with less therapy, limiting the physical and financial toxicity associated with years of treatment. Well-designed trials are needed to identify optimal duration of therapy, and to define biomarkers to predict who would benefit from shorter courses of immunotherapy. Here, we outline key questions related to health, financial and societal toxicities of over treating with ICI and present four unique clinical trials aimed at exposing criteria for early cessation of ICI. Taken together, there is a serious liability to overtreating patients with ICI and future work is warranted to determine when it is safe to stop ICI.

Background Inflammatory breast cancer (IBC) has a highly invasive and metastatic phenotype. However, little is known about its genetic drivers. To address this, we report the largest cohort of whole-genome sequencing (WGS) of IBC cases. Methods We performed WGS of 20 IBC samples and paired normal blood DNA to identify genomic alterations. For comparison, we used 23 matched non-IBC samples from the Cancer Genome Atlas Program (TCGA). We also validated our findings using WGS data from the International Cancer Genome Consortium (ICGC) and the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium. We examined a wide selection of genomic features to search for differences between IBC and conventional breast cancer. These include (i) somatic and germline single-nucleotide variants (SNVs), in both coding and non-coding regions; (ii) the mutational signature and the clonal architecture derived from these SNVs; (iii) copy number and structural variants (CNVs and SVs); and (iv) non-human sequence in the tumors (i.e., exogenous sequences of bacterial origin). Results Overall, IBC has similar genomic characteristics to non-IBC, including specific alterations, overall mutational load and signature, and tumor heterogeneity. In particular, we observed similar mutation frequencies between IBC and non-IBC, for each gene and most cancer-related pathways. Moreover, we found no exogenous sequences of infectious agents specific to IBC samples. Even though we could not find any strongly statistically distinguishing genomic features between the two groups, we did find some suggestive differences in IBC: (i) The MAST2 gene was more frequently mutated (20% IBC vs. 0% non-IBC). (ii) The TGF β pathway was more frequently disrupted by germline SNVs (50% vs. 13%). (iii) Different copy number profiles were observed in several genomic regions harboring cancer genes. (iv) Complex SVs were more frequent. (v) The clonal architecture was simpler, suggesting more homogenous tumor-evolutionary lineages. Conclusions Whole-genome sequencing of IBC manifests a similar genomic architecture to non-IBC. We found no unique genomic alterations shared in just IBCs; however, subtle genomic differences were observed including germline alterations in TGFβ pathway genes and somatic mutations in the MAST2 kinase that could represent potential therapeutic targets.

BackgroundCyclin-dependent kinase 4/6 inhibitors (CDK4/6i) combined with endocrine therapy are a mainstay treatment for hormone receptor-positive breast cancer. While their principal mechanism is inhibition of cancer cell proliferation, preclinical and clinical evidence suggests that CDK4/6i can also promote antitumor T-cell responses. However, this pro-immunogenic property is yet to be successfully harnessed in the clinic, as combining CDK4/6i with immune checkpoint blockade (ICB) has not shown a definitive benefit in patients.MethodWe performed an in-depth analysis of the changes in the tumor immune microenvironment and systemic immune modulation associated with CDK4/6i treatment in muring breast cancer models and in patients with breast cancer using high dimensional flow cytometry and RNA sequencing. Gain and loss of function in vivo experiments employing cell transfer and depletion antibody were performed to uncover immune cell populations critical for CDK4/6i-mediated stimulation of antitumor immunity.ResultsWe found that loss of dendritic cells (DCs) within the tumor microenvironment resulting from CDK4/6 inhibition in bone marrow progenitors is a major factor limiting antitumor immunity after CDK4/6i and ICB. Consequently, restoration of DC compartment by adoptively transferring ex vivo differentiated DCs to mice treated with CDK4/6i and ICB therapy enabled robust tumor inhibition. Mechanistically, the addition of DCs promoted the induction of tumor-localized and systemic CD4 T-cell responses in mice receiving CDK4/6i-ICB-DC combination therapy, as characterized by enrichment of programmed cell death protein-1-negative T helper (Th)1 and Th2 cells with an activated phenotype. CD4 T-cell depletion abrogated the antitumor benefit of CDK4/6i-ICB-DC combination, with outgrowing tumors displaying an increased proportion of terminally exhausted CD8 T cells.ConclusionsOur findings suggest that CDK4/6i-mediated DC suppression limits CD4 T-cell responses essential for the sustained activity of CD8 T cells and tumor inhibition. Furthermore, they imply that restoring DC-CD4 T-cell crosstalk via DC transfer enables effective breast cancer immunity in response to CDK4/6i and ICB treatment.

Background The Dallas Metastatic Cancer Study is a clinical database established to examine local trends associated with the diagnosis and treatment of de novo metastatic breast cancer and identify factors for further evaluation. Clinical characteristics of patients with de novo metastatic breast cancer are often underreported in the literature. Methods We report data from 2010 to 2021 for patients with de novo metastatic breast cancer along with the impact of clinical variables such as age, BMI, race and ethnicity, insurance status, hypertension, diabetes, and site of metastasis with survival analysis with respect to subtype. Results Black race (HR 2.07, 95% CI 1.56–2.74), public insurance (HR 1.64, 95% CI 1.23–2.18), no insurance (HR 1.69, 95% CI 1.24–2.31), hypertension (HR 1.50, 95% CI 1.18–1.91), diabetes (HR 1.69, 95% CI 1.24–2.31), and visceral metastases including brain (HR 1.68, 95% CI 1.20–2.36), liver (HR 1.80, 95% CI 1.40–2.30), and lung (HR 1.50, 95% CI 1.17–1.92) were associated with increased mortality and remained significant when controlled for subtype. In the multivariate analysis, diabetes (HR 1.74, 95% CI 1.22–2.49) and presence of liver metastases (HR 1.97, 95% CI 1.43–2.49) remained independently associated with decreased overall survival regardless of subtype and other variables. Patients diagnosed at 40 and younger were less likely to have hypertension and diabetes, more likely to be Hispanic, and showed distinct subtype distributions compared to those diagnosed at older ages. Conclusions Future work will focus on these associations at the patient level to identify targets for intervention. Plain language summary The Dallas Metastatic Cancer Study aims to better understand metastatic breast cancer by examining local trends in diagnosis and treatment. The study analyzed data from 2010 to 2021 and specifically focused on patients with a metastatic breast cancer diagnosis at first presentation. The study evaluated how factors such as age, BMI, race, insurance status, and co-existing medical conditions like hypertension and diabetes affected survival. The results show that Black patients, those with public or no insurance, those with specific metastases (i.e., liver, brain, lung) had worse survival outcomes. These outcomes underscore the areas where targeted interventions could improve patient outcomes. Chang, Cao et al. examine local trends associated with the diagnosis and treatment of de novo metastatic breast cancer. Findings show that black race, hypertension, diabetes, as well as the presence of visceral metastases are associated with a worse prognosis.

Preclinical studies suggest that treatment with neoadjuvant immune checkpoint blockade is associated with enhanced survival and antigen-specific T cell responses compared with adjuvant treatment 1 ; however, optimal regimens have not been defined. Here we report results from a randomized phase 2 study of neoadjuvant nivolumab versus combined ipilimumab with nivolumab in 23 patients with high-risk resectable melanoma ( NCT02519322 ). RECIST overall response rates (ORR), pathologic complete response rates (pCR), treatment-related adverse events (trAEs) and immune correlates of response were assessed. Treatment with combined ipilimumab and nivolumab yielded high response rates (RECIST ORR 73%, pCR 45%) but substantial toxicity (73% grade 3 trAEs), whereas treatment with nivolumab monotherapy yielded modest responses (ORR 25%, pCR 25%) and low toxicity (8% grade 3 trAEs). Immune correlates of response were identified, demonstrating higher lymphoid infiltrates in responders to both therapies and a more clonal and diverse T cell infiltrate in responders to nivolumab monotherapy. These results describe the feasibility of neoadjuvant immune checkpoint blockade in melanoma and emphasize the need for additional studies to optimize treatment regimens and to validate putative biomarkers. Neoadjuvant combination treatment with nivolumab and ipilimumab in patients with high-risk melanoma results in higher response rates than nivolumab monotherapy and warrants future optimization of dosing regimens to preserve efficacy while limiting toxicity.

Breast cancer metastases exhibit many different genetic alterations, including copy number amplifications (CNA). CNA are genetic alterations that are increasingly becoming relevant to breast oncology clinical practice. Here we identify CNA in metastatic breast tumor samples using publicly available datasets and characterize their expression and function using a metastatic mouse model of breast cancer. Our findings demonstrate that our organoid generation can be implemented to study clinically relevant features that reflect the genetic heterogeneity of individual tumors.

Complex tumor microenvironmental (TME) features influence the outcome of cancer immunotherapy (IO). Here we perform immunogenomic analyses on 67 intratumor sub-regions of a PD-1 inhibitor-resistant melanoma tumor and 2 additional metastases arising over 8 years, to characterize TME interactions. We identify spatially distinct evolution of copy number alterations influencing local immune composition. Sub-regions with chromosome 7 gain display a relative lack of leukocyte infiltrate but evidence of neutrophil activation, recapitulated in The Cancer Genome Atlas (TCGA) samples, and associated with lack of response to IO across three clinical cohorts. Whether neutrophil activation represents cause or consequence of local tumor necrosis requires further study. Analyses of T-cell clonotypes reveal the presence of recurrent priming events manifesting in a dominant T-cell clonotype over many years. Our findings highlight the links between marked levels of genomic and immune heterogeneity within the physical space of a tumor, with implications for biomarker evaluation and immunotherapy response. Immunotherapies now dominate the treatment landscape for melanoma, but why they only work in a subset of patients remains unclear. Here, the authors perform an immunogenomic analysis on 67 intratumor sub-regions of a PD-1 inhibitor resistant melanoma, and 2 additional metastases from a single patient, mapping the spatial relationships between genomic and immune heterogeneity at high resolution.

BackgroundBreast cancers have shown limited responses to current FDA approved forms of immunotherapy. Defective antigen presentation in breast cancers contributes to this deficient anti-tumor immunity. Flt3 ligand (Flt3L) is a growth factor that increases differentiation of cDC1 dendritic cells, critical mediators of antigen presentation. CD40 agonist (CD40a) activates all 3 classes of antigen presenting cells - dendritic cells, B cells, and macrophages. Synergy has been demonstrated between Flt3L and CD40a as well as between CD40a and chemotherapy in other cancers, however the combination of all three has not been studied in breast cancer.Methods6–8 week old C57BL/6 mice were injected with E0771 breast cancer cells. When tumors were 50 mm3, mice were first treated with pegylated liposomal doxorubicin (PLD) once by tail vein followed by Flt3L intraperitoneal (IP) daily for 5 days and then CD40a IP 1 week after. Tumor volumes were measured serially to assess pre-clinical activity of the drug combinations. To assess mechanism of action, tumors and lymph nodes were harvested from sacrificed mice for single cell RNA sequencing and immunohistochemistry analysis.ResultsTreatment with PLD, Flt3L, and CD40a led to improved tumor control compared to control, PLD monotherapy, CD40a monotherapy, Flt3L monotherapy, PLD + Flt3L doublet, and PLD + CD40a doublet (p<0.0001). Immunohistochemistry revealed an increase in CD8 T cell infiltration into the tumor microenvironment with addition of CD40a and Flt3L to PLD chemotherapy. Single cell RNA sequencing demonstrated Flt3L addition to PLD chemotherapy induced an increase in intra-tumoral cDC1 and other dendritic cell subsets with Flt3L treatment. CD40a addition to PLD instead led to a decrease in DC subsets in the tumor likely from activation and emigration, repolarization of intra-tumoral macrophages, and class switching of lymph node B cells. Addition of Flt3L and CD40a to PLD in triplet combination led to both sets of changes.ConclusionsNovel triplet combination with PLD, CD40a, and Flt3L leads to enhanced tumor control in the E0771 breast cancer mouse model. A clinical trial with this combination in metastatic triple negative breast cancer patients is open and recruiting (NCT05029999).Ethics ApprovalThe research was conducted in accordance with the ethical guidelines set forth by the Institutional Animal Care and Use Committee (IACUC).