The immune system and hormone-receptor positive breast cancer: Is it really a dead end?

Extracellular vesicles reshape the tumor microenvironment to improve cancer immunotherapy: Current knowledge and future prospects

Tumor immunotherapy has revolutionized cancer treatment, but limitations remain, including low response rates and immune complications. Extracellular vesicles (EVs) are emerging as a new class of therapeutic agents for various diseases. Recent research shows that changes in the amount and composition of EVs can reshape the tumor microenvironment (TME), potentially improving the effectiveness of immunotherapy. This exciting discovery has sparked clinical interest in using EVs to enhance the immune system's response to cancer. In this Review, we delve into the world of EVs, exploring their origins, how they're generated, and their complex interactions within the TME. We also discuss the crucial role EVs play in reshaping the TME during tumor development. Specifically, we examine how their cargo, including molecules like PD-1 and non-coding RNA, influences the behavior of key immune cells within the TME. Additionally, we explore the current applications of EVs in various cancer therapies, the latest advancements in engineering EVs for improved immunotherapy, and the challenges faced in translating this research into clinical practice. By gaining a deeper understanding of how EVs impact the TME, we can potentially uncover new therapeutic vulnerabilities and significantly enhance the effectiveness of existing cancer immunotherapies.

Tumor-Associated Neutrophils Are a Negative Prognostic Factor in Early Luminal Breast Cancers Lacking Immunosuppressive Macrophage Recruitment

BACKGROUND

Tumor-associated neutrophils (TANs) are important modulators of the tumor microenvironment with opposing functions that can promote and inhibit tumor progression. The prognostic role of TANs in early luminal breast cancer is unclear.

METHODS

A total of 144 patients were treated for early-stage hormone-receptor-positive breast cancer as part of an Accelerated Partial Breast Irradiation (APBI) phase II trial. Resection samples from multiple locations were processed into tissue microarrays and sections thereof immunohistochemically stained for CD66b+ neutrophils. CD66b+ neutrophil density was measured separately in the stromal and intraepithelial compartment.

RESULTS

High stromal and intraepithelial CD66b+ TAN density was a negative prognostic factor in central tumor samples. In addition, neutrophil density in adjacent normal breast tissue and lymph node samples also correlated with reduced disease-free survival. TAN density correlated with CD163+ M2-like tumor-associated macrophage (TAM) density, which we analyzed in a previous study. TANs were a negative prognostic factor in tumors with an elevated M1/M2 TAM ratio, while this impact on patient outcome was lost in tumors with a low M1/M2 ratio. A combined multivariate analysis of TAM and TAN density revealed that only TAM polarization status was an independent prognostic factor.

CONCLUSIONS

CD66b+ neutrophils were a negative prognostic factor in early-stage luminal breast cancer in single-marker analysis. Combined analysis with TAMs could be necessary to correctly evaluate their prognostic impact in future studies. TAN recruitment might act as a compensatory mechanism of immunoevasion and disease progression in tumors that are unable to sufficiently attract and polarize TAMs.

Tumor-Infiltrating Lymphocytes (TILs) in Breast Cancer: Prognostic and Predictive Significance across Molecular Subtypes

Tumor-infiltrating lymphocytes (TILs) are pivotal in the immune response against breast cancer (BC), with their prognostic and predictive significance varying across BC subtypes. In triple-negative BC (TNBC), higher TIL levels correlate with improved prognosis and treatment response, guiding therapeutic strategies and potentially offering avenues for treatment de-escalation. In metastatic TNBC, TILs identify patients with enhanced immunotherapy response. HER2+ BC, similar to TNBC, exhibits positive correlations between TILs and treatment response, especially in neoadjuvant settings. Luminal BC generally has low TILs, with limited prognostic impact. Single hormone receptor-positive BCs show distinct TIL associations, emphasizing subtype-specific considerations. TILs in ductal carcinoma in situ (DCIS) display ambiguous prognostic significance, necessitating further investigation. Standardizing TIL assessment methods is crucial for unlocking their full potential as biomarkers, guiding treatment decisions, and enhancing patient care in BC.

Experimental and clinical evidence in favour of an effective immune stimulation in ER-positive, endocrine-dependent metastatic breast cancer

In ER+ breast cancer, usually seen as the low immunogenic type, the main mechanisms favouring the immune response or tumour growth and immune evasion in the tumour microenvironment (TME) have been examined. The principal implications of targeting the oestrogen-mediated pathways were also considered. Recent experimental findings point out that anti-oestrogens contribute to the reversion of the immunosuppressive TME. Moreover, some preliminary clinical data with the hormone-immunotherapy association in a metastatic setting support the notion that the reversion of immune suppression in TME is likely favoured by the G0-G1 state induced by anti-oestrogens. Following immune stimulation, the reverted immune suppression allows the boosting of the effector cells of the innate and adaptive immune response. This suggests that ER+ breast cancer is a molecular subtype where a successful active immune manipulation can be attained. If this is confirmed by a prospective multicentre trial, which is expected in light of the provided evidence, the proposed hormone immunotherapy can also be tested in the adjuvant setting. Furthermore, the different rationale suggests a synergistic activity of our proposed immunotherapy with the currently recommended regimen consisting of antioestrogens combined with cyclin kinase inhibitors. Overall, this lays the foundation for a shift in clinical practice within this most prevalent molecular subtype of breast cancer.

Identification of a Panel of miRNAs Associated with Resistance to Palbociclib and Endocrine Therapy

We investigated whether we could identify a panel of miRNAs associated with response to treatment in tumor tissues of patients with Hormone Receptor-positive/HER2-negative metastatic breast cancer treated with endocrine therapy (ET) and the CDK4/6 inhibitor (CDK4/6i)i palbociclib. In total, 52 patients were evaluated, with 41 receiving treatment as the first line. The overall median PFS was 20.8 months (range 2.5-66.6). In total, 23% of patients experienced early progression (<6 months). Seven miRNAs (miR-378e, miR-1233, miR-99b-5p, miR-1260b, miR-448, -miR-1252-5p, miR-324-3p, miR-1233-3p) showed a statistically significant negative association with PFS. When we considered PFS < 6 months, miR-378e, miR-99b-5p, miR-877-5p, miR-1297, miR-455-5p, and miR-4536-5p were statistically associated with a poor outcome. In the multivariate analysis, the first three miRNAs confirmed a significant and independent impact on PFS. The literature data and bioinformatic tools provide an underlying molecular rationale for most of these miRNAs, mainly involving the PI3K/AKT/mTOR pathway and cell-cycle machinery as cyclin D1, CDKN1B, and protein p27Kip1 and autophagy. Our findings propose a novel panel of miRNAs associated with a higher likelihood of early progression in patients treated with ET and Palbociclib and may contribute to shed some light on the mechanisms of de novo resistance to CDK4/6i, but this should be considered exploratory and evaluated in larger cohorts.

Extracellular vesicles remodel tumor environment for cancer immunotherapy

Tumor immunotherapy has transformed neoplastic disease management, yet low response rates and immune complications persist as major challenges. Extracellular vesicles including exosomes have emerged as therapeutic agents actively involved in a diverse range of pathological conditions. Mounting evidence suggests that alterations in the quantity and composition of extracellular vesicles (EVs) contribute to the remodeling of the immune-suppressive tumor microenvironment (TME), thereby influencing the efficacy of immunotherapy. This revelation has sparked clinical interest in utilizing EVs for immune sensitization. In this perspective article, we present a comprehensive overview of the origins, generation, and interplay among various components of EVs within the TME. Furthermore, we discuss the pivotal role of EVs in reshaping the TME during tumorigenesis and their specific cargo, such as PD-1 and non-coding RNA, which influence the phenotypes of critical immune cells within the TME. Additionally, we summarize the applications of EVs in different anti-tumor therapies, the latest advancements in engineering EVs for cancer immunotherapy, and the challenges encountered in clinical translation. In light of these findings, we advocate for a broader understanding of the impact of EVs on the TME, as this will unveil overlooked therapeutic vulnerabilities and potentially enhance the efficacy of existing cancer immunotherapies.

Association of tumor-infiltrating lymphocytes with recurrence score in hormone receptor-positive/HER2-negative breast cancer: Analysis of four prospective studies

BACKGROUND

The clinical value of tumor infiltrating lymphocytes (TILs) in hormone receptor-positive (HR+)/HER2- breast cancer (BC) may be unearthed by focusing on more biologically aggressive tumors. Here we deepen and describe the correlation between RS and TILs, proposing an immuno-genomic model for HR+ /HER2- BC.

METHODS

We enrolled T1-T3, N0-N1 BC patients with available RS® and TILs in the context of four multicenter, prospective studies. RS® and TILs were considered as continuous and categorical variables. RS® was categorized into: 0-10 (low risk), 11-25 (intermediate risk) and 26-100 (high risk); TILs were categorized into: low TILs (0-10%), intermediate TILs (11-59%) and high TILs (60-100%).

RESULTS

811 patients were included. RS distribution was (n = 810): low risk 22.0%, intermediate risk 61.2%, high risk 16.8%. TIL distribution was (n = 455): low TILs 84.6%, intermediate TILs 13.6% and high TILs 1.8%. A significant, weak positive, linear correlation was found between continuous TILs and RS (Pearson coefficient=0.223, p < 0.001). When considering RS and TILs categories, tumors with intermediate/high TIL levels significantly enriched the high RS subgroup (p = 0.006). This was confirmed both within Luminal A and Luminal B cohorts. Among high-RS patients, 16.7% of Luminal A and 26.7% of Luminal B tumors had intermediate/high TILs.

CONCLUSIONS

We observed that RS® and TILs capture only slightly overlapping information on the biology of HR+ /HER2- tumor microenvironment. We demonstrated the feasibility of combining RS and TILs into a composite immuno-genomic model, which may serve the purpose of guiding and focalizing patient selection in the further development of immunotherapy strategies for Luminal-like disease.

Evaluation of tumour infiltrating lymphocytes in luminal breast cancer using artificial intelligence

BACKGROUND

Tumour infiltrating lymphocytes (TILs) are a prognostic parameter in triple-negative and human epidermal growth factor receptor 2 (HER2)-positive breast cancer (BC). However, their role in luminal (oestrogen receptor positive and HER2 negative (ER + /HER2-)) BC remains unclear. In this study, we used artificial intelligence (AI) to assess the prognostic significance of TILs in a large well-characterised cohort of luminal BC.

METHODS

Supervised deep learning model analysis of Haematoxylin and Eosin (H&E)-stained whole slide images (WSI) was applied to a cohort of 2231 luminal early-stage BC patients with long-term follow-up. Stromal TILs (sTILs) and intratumoural TILs (tTILs) were quantified and their spatial distribution within tumour tissue, as well as the proportion of stroma involved by sTILs were assessed. The association of TILs with clinicopathological parameters and patient outcome was determined.

RESULTS

A strong positive linear correlation was observed between sTILs and tTILs. High sTILs and tTILs counts, as well as their proximity to stromal and tumour cells (co-occurrence) were associated with poor clinical outcomes and unfavourable clinicopathological parameters including high tumour grade, lymph node metastasis, large tumour size, and young age. AI-based assessment of the proportion of stroma composed of sTILs (as assessed visually in routine practice) was not predictive of patient outcome. tTILs was an independent predictor of worse patient outcome in multivariate Cox Regression analysis.

CONCLUSION

AI-based detection of TILs counts, and their spatial distribution provides prognostic value in luminal early-stage BC patients. The utilisation of AI algorithms could provide a comprehensive assessment of TILs as a morphological variable in WSIs beyond eyeballing assessment.

A Mendelian randomization-based approach to explore the relationship between leukocyte counts and breast cancer risk in European ethnic groups

Exploring the potential association between peripheral blood leukocyte counts and breast cancer risk by Mendelian randomization (MR) analysis methods. Genetic data related to peripheral blood sorting counts of leukocytes were collected from a genome-wide association study by Blood Cell Consortium (BCX). Single nucleotide polymorphic loci predicting peripheral blood sorting counts of these leukocytes were selected as instrumental variables according to the correlation assumption, independence assumption and exclusivity assumption of MR. The data on breast cancer and its subtypes were obtained from Breast Cancer Association Consortium (BCAC) and FinnGen Consortium. In this study, the Inverse-Variance Weighted (IVW), Weighted Median, MR-Egger, Maximum Likelihood (ML), MR-PRESSO and Constrained Maximum Likelihood and Model Averaging (cML-MA) methods of random effects models were used for MR analysis. Cochran's Q analysis, and MR-Egger intercept analysis were applied for sensitivity analysis. IVW and cML-MA were considered the primary analytical tools, and the results of the other 4 MRs were used as complementary and validation. The results suggest that there is no significant causal relationship between leukocyte count and breast cancer risk (IVW OR = 0.98 [95% CI: 0.93-1.03], p-value = 0.35; CML-MA OR = 1.01 [95% CI: 0.98-1.05], p-value = 0.51). In addition, we analyzed whether there was a potential correlation between the five main types of categorized leukocyte counts and different breast cancer subtypes. We did not find significant evidence to support a significant correlation between leukocyte counts and breast cancer subtypes.

Positive p53 Expression Is Associated with Primary Endocrine Therapy Resistance in Locally Advanced Stage Luminal B HER2-Negative Breast Cancer Patients: A Cross-Sectional Study in Indonesia

Luminal B HER2-negative breast cancer (BC) is the most common type in Indonesian BC patients, and frequently manifests with locally advanced staging. Recurrence often occurs within two years of the endocrine therapy course (primary endocrine therapy (ET) resistance). p53 mutation often exists in luminal B HER2-negative BC, but its application as an ET resistance predictor in those populations is still limited. The primary purpose of this research is to evaluate p53 expression and its association with primary ET resistance in luminal B HER2-negative BC. This cross-sectional study compiled 67 luminal B HER2-negative patients' clinical data during their pre-treatment period until they completed a two-year course of endocrine therapy. They were divided into two groups: 29 patients with primary ET resistance and 38 without primary ET resistance. Pre-treatment paraffin blocks from each patient were retrieved, and the p53 expression difference between the two groups was analyzed. Positive p53 expression was significantly higher in patients with primary ET resistance [odds ratio (OR) of 11.78 (95% CI: 3.72-37.37, p-value < 0.0001)]. We conclude that p53 expression could be a beneficial marker for primary ET resistance in locally advanced luminal B HER2-negative BC.

Impact of microbiota on breast cancer hormone therapy

Recent observations indicate that the pathogenesis and prognosis of hormone-receptor breast cancer is not only dictated by the properties of the malignant cells but also by immune and microbial parameters. Thus, the immunosurveillance system retards the development of hormone-positive breast cancer and contributes to the therapeutic efficacy of estrogen receptor antagonists and aromatase inhibitors. Moreover, the anticancer immune response is profoundly modulated by the local and intestinal microbiota, which influences cancer cell-intrinsic signaling pathways, affects the composition and function of the immune infiltrate present in the tumor microenvironment and modulates the metabolism of estrogens. Indeed, specific bacteria in the gut produce enzymes that affect the enterohepatic cycle of estrogen metabolites, convert estrogens into androgens or generate estrogen-like molecules. The knowledge of these circuitries is in its infancy, calling for further in-depth analyses.

Expression of hormone receptors is associated with specific immunological profiles of the breast cancer microenvironment

BACKGROUND

Elucidating the unique immunoregulatory mechanisms in breast cancer microenvironment may help develop new therapeutic strategies. Some studies have suggested that hormone receptors also have immune regulatory functions, but their mechanisms are not fully understood. In this study, we have comprehensively analyzed the relationship between the expressions of estrogen (ER), progesterone (PgR), and androgen receptors (AR), and the immunological profile in breast cancer.

METHODS

Using publicly available gene expression profile datasets, METABRIC and SCAN-B, the associations between the expressions of hormone receptors and the immune cell compositions in breast cancer tissue, estimated by CIBERSORTx algorithm, were analyzed. We histologically evaluated tumor-infiltrating lymphocytes (hTIL), PD-L1 (hPD-L1) expression, and the infiltration of 11 types of immune cells by flow cytometry (FCM) for 45 breast cancer tissue samples. The relationships between them and the expressions of ER, PgR, and AR of tumor tissues, evaluated immunohistochemically, were analyzed.

RESULTS

Expressions of ESR1, PGR, and AR were negatively correlated with overall immune composition. Expressions of ER and AR, but not that of PgR, were inversely associated with hTIL and hPD-L1 expression. FCM analysis showed that the expressions of ER and AR, but not that of PgR, were associated with decreased total leukocyte infiltration. Both CIBERSORTx and FCM analysis showed that ER expression was associated with reduced infiltration of macrophages and CD4+ T cells and that of AR with reduced macrophage infiltration.

CONCLUSION

Hormone receptor expression correlates with specific immunological profiles in the breast cancer microenvironment both at the gene and protein expression levels.

Immune Checkpoint Inhibitors in Cancer Therapy-How Can We Improve Clinical Benefits?

Immune checkpoint inhibitors (ICIs) are in the spotlight of cancer treatment by increasing the probability for long-term survival in patients with metastatic disease and by considerably prolonging progression-free survival in patients at early disease stages [...].

On-treatment derived neutrophil-to-lymphocyte ratio and survival with palbociclib and endocrine treatment: analysis of a multicenter retrospective cohort and the PALOMA-2/3 study with immune correlates

BACKGROUND

Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors have been established as a standard treatment for hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer (ABC); however, predictive biomarkers with translational relevance have not yet been elucidated.

METHODS

Data from postmenopausal women who received the CDK4/6 inhibitor palbociclib and letrozole for HR-positive, HER2-negative ABC from tertiary referral centers were analyzed (N = 221; exploratory cohort). Pre- and on-treatment neutrophil-to-lymphocyte ratio (NLR) and derived NLR (dNLR; neutrophil/[leukocyte-neutrophil]) were correlated with survival outcomes. Data from the PALOMA-2 (NCT01740427) and PALOMA-3 studies (NCT01942135) involving patients treated with endocrine treatment with or without palbociclib were also analyzed (validation cohort). Prospectively enrolled patients (N = 20) were subjected to immunophenotyping with circulating immune cells to explore the biological implications of immune cell dynamics.

RESULTS

In the exploratory cohort, palbociclib administration significantly reduced leukocyte, neutrophil, and lymphocyte counts on day 1 of cycle 2. Although the baseline dNLR was not significantly associated with progression-free survival (PFS), higher on-treatment dNLRs were associated with worse PFS (hazard ratio = 3.337, P < 0.001). In the PALOMA-2 validation cohort, higher on-treatment dNLRs were associated with inferior PFS in patients treated with palbociclib and letrozole (hazard ratio = 1.498, P = 0.009), and reduction in the dNLR after treatment was predictive of a survival benefit (hazard ratio = 1.555, P = 0.026). On-treatment dNLRs were also predictive of PFS following palbociclib and fulvestrant treatment in the PALOMA-3 validation cohort. Using flow cytometry analysis, we found that the CDK4/6 inhibitor prevented T cell exhaustion and diminished myeloid-derived suppressor cell frequency.

CONCLUSIONS

On-treatment dNLR significantly predicted PFS in patients with HR-positive, HER2-negative ABC receiving palbociclib and endocrine treatment. Additionally, we observed putative systemic immune responses elicited by palbociclib, suggesting immunologic changes upon CDK4/6 inhibitor treatment.

Co-Targeting Luminal B Breast Cancer with S-Adenosylmethionine and Immune Checkpoint Inhibitor Reduces Primary Tumor Growth and Progression, and Metastasis to Lungs and Bone

Breast cancer (BCa) is the most prevalent cancer in females and has a high rate of mortality, especially due to increased metastasis to skeletal and non-skeletal sites. Despite the marked clinical accomplishment of immune checkpoint inhibitor (CPI) therapy in patients with several cancers, it has had limited success in luminal subtypes of BCa. Accordingly, recent efforts have focused on combination therapy with CPI, including epigenetic modulators, to increase response rates of CPI in luminal BCa. We have previously shown that S-adenosylmethionine (SAM), the ubiquitous methyl donor, has strong anti-cancer effects in various cancers, including all subtypes of BCa. In the current study, we took a novel approach and examined the effect of CPI alone and in combination with SAM on tumor growth and metastasis in a syngeneic mouse model of luminal B BCa. We showed that SAM decreases cell proliferation, colony-formation (survival), and invasion of luminal B BCa cell lines (Eo771, R221A) in vitro. In in vivo studies, in Eo771 tumor-bearing mice, either SAM or anti-PD-1 antibody treatment alone significantly reduced tumor growth and progression, while the SAM+anti-PD-1 combination treatment had the highest anti-cancer efficacy of all groups. The SAM+anti-PD-1 combination reduced the percentage of animals with lung metastasis, as well as total metastatic lesion area, compared to control. Additionally, the SAM+anti-PD-1 combination significantly reduced the skeletal lesion area and protected tibial integrity to a greater extent than the monotherapies in an Eo771 bone metastasis model. Transcriptome analysis of Eo771 primary tumors revealed significant downregulation of pro-metastatic genes, including Matrix metalloproteinases (MMPs) and related pathways. On the other hand, CD8⁺ T cell infiltration, CD8⁺ T cell cytotoxicity (elevated granzymes), and immunostimulatory genes and pathways were significantly upregulated by the combination treatment. The results presented point to a combination of SAM with CPI as a possible treatment for luminal B BCa that should be tested in clinical studies.

Multiplexed In Situ Spatial Protein Profiling in the Pursuit of Precision Immuno-Oncology for Patients with Breast Cancer

Immune checkpoint inhibitors (ICIs) have revolutionized the treatment of many solid tumors. In breast cancer (BC), immunotherapy is currently approved in combination with chemotherapy, albeit only in triple-negative breast cancer. Unfortunately, most patients only derive limited benefit from ICIs, progressing either upfront or after an initial response. Therapeutics must engage with a heterogeneous network of complex stromal-cancer interactions that can fail at imposing cancer immune control in multiple domains, such as in the genomic, epigenomic, transcriptomic, proteomic, and metabolomic domains. To overcome these types of heterogeneous resistance phenotypes, several combinatorial strategies are underway. Still, they can be predicted to be effective only in the subgroups of patients in which those specific resistance mechanisms are effectively in place. As single biomarker predictive performances are necessarily suboptimal at capturing the complexity of this articulate network, precision immune-oncology calls for multi-omics tumor microenvironment profiling in order to identify unique predictive patterns and to proactively tailor combinatorial treatments. Multiplexed single-cell spatially resolved tissue analysis, through precise epitope colocalization, allows one to infer cellular functional states in view of their spatial organization. In this review, we discuss-through the lens of the cancer-immunity cycle-selected, established, and emerging markers that may be evaluated in multiplexed spatial protein panels to help identify prognostic and predictive patterns in BC.

Comparative biomarker analysis of PALOMA-2/3 trials for palbociclib

While cyclin-dependent kinase 4/6 (CDK4/6) inhibitors, including palbociclib, combined with endocrine therapy (ET), are becoming the standard-of-care for hormone receptor-positive/human epidermal growth factor receptor 2‒negative metastatic breast cancer, further mechanistic insights are needed to maximize benefit from the treatment regimen. Herein, we conducted a systematic comparative analysis of gene expression/progression-free survival relationship from two phase 3 trials (PALOMA-2 [first-line] and PALOMA-3 [≥second-line]). In the ET-only arm, there was no inter-therapy line correlation. However, adding palbociclib resulted in concordant biomarkers independent of initial ET responsiveness, with shared sensitivity genes enriched in estrogen response and resistance genes over-represented by mTORC1 signaling and G2/M checkpoint. Biomarker patterns from the combination arm resembled patterns observed in ET in advanced treatment-naive patients, especially patients likely to be endocrine-responsive. Our findings suggest palbociclib may recondition endocrine-resistant tumors to ET, and may guide optimal therapeutic sequencing by partnering CDK4/6 inhibitors with different ETs. Pfizer (NCT01740427; NCT01942135).

A comprehensive profiling of the immune microenvironment of breast cancer brain metastases

BACKGROUND

Despite potential clinical implications, the complexity of breast cancer (BC) brain metastases (BM) immune microenvironment is poorly understood. Through multiplex immunofluorescence, we here describe the main features of BCBM immune microenvironment (density and spatial distribution) and evaluate its prognostic impact.

METHODS

Sixty BCBM from patients undergoing neurosurgery at three institutions (2003-2018) were comprehensively assessed using two multiplex immunofluorescence panels (CD4, CD8, Granzyme B, FoxP3, CD68, pan-cytokeratin, DAPI; CD3, PD-1, PD-L1, LAG-3, TIM-3, CD163, pan-cytokeratin, DAPI). The prognostic impact of immune subpopulations and cell-to-cell spatial interactions was evaluated.

RESULTS

Subtype-related differences in BCBM immune microenvironment and its prognostic impact were observed. While in HR-/HER2- BM and HER2+ BM, higher densities of intra-tumoral CD8+ lymphocytes were associated with significantly longer OS (HR 0.16 and 0.20, respectively), in HR+/HER2- BCBMs a higher CD4+FoxP3+/CD8+ cell ratio in the stroma was associated with worse OS (HR 5.4). Moreover, a higher density of intra-tumoral CD163+ M2-polarized microglia/macrophages in BCBMs was significantly associated with worse OS in HR-/HER2- and HR+/HER2- BCBMs (HR 6.56 and 4.68, respectively), but not in HER2+ BCBMs. In HER2+ BCBMs, multiplex immunofluorescence highlighted a negative prognostic role of PD-1/PD-L1 interaction: patients with a higher percentage of PD-L1+ cells spatially interacting with (within a 20 µm radius) PD-1+ cells presented a significantly worse OS (HR 4.60).

CONCLUSIONS

Our results highlight subtype-related differences in BCBM immune microenvironment and identify two potential therapeutic targets, M2 microglia/macrophage polarization in HER2- and PD-1/PD-L1 interaction in HER2+ BCBMs, which warrant future exploration in clinical trials.

Immunological profiles of the breast cancer microenvironment represented by tumor-infiltrating lymphocytes and PD-L1 expression

Tumor-infiltrating lymphocytes (TILs) and programmed cell death 1 ligand 1 (PD-L1) are established prognostic and predictive biomarkers for certain breast cancer subsets. However, their association with the immune response complexity is not fully understood. Therefore, we analyzed the association between the immune cell fractions in breast cancer tissues and histologically assessed TIL (hTIL) and PD-L1 (hPD-L1). Forty-five tumor and eighteen blood samples were collected from patients with breast cancer. Total leukocyte counts, frequency of 11 immune cell populations, and PD-L1 expression in each cell fraction were evaluated by flow cytometry. TILs and PD-L1 were assessed by hematoxylin and eosin staining and immunohistochemistry, respectively. A higher hTIL score showed association with increased leukocyte infiltration, higher CD4⁺ and CD8⁺ T cell proportions, and lower natural killer and natural killer T cell proportions. PD-L1 was highly expressed in nonclassical monocytes, monocyte/macrophages, myeloid-derived suppressor cells, myeloid dendritic cells, dendritic cells, and other lineages in tumors. hPD-L1 positivity reflected PD-L1 expression accurately in these fractions, as well as increased leukocyte infiltration in tumors. These results indicate that hTILs reflect differences in the immune responses in the tumor microenvironment, and certain immune cell fractions are favorably expressed in the PD-L1 pathway in breast cancer microenvironments.

Neoadjuvant Chemotherapy and Immunotherapy in Luminal B-like Breast Cancer: Results of the Phase II GIADA Trial

PURPOSE

The role of immunotherapy in hormone receptor (HR)-positive, HER2-negative breast cancer is underexplored.

PATIENTS AND METHODS

The neoadjuvant phase II GIADA trial (NCT04659551, EUDRACT 2016-004665-10) enrolled stage II-IIIA premenopausal patients with Luminal B (LumB)-like breast cancer (HR-positive/HER2-negative, Ki67 ≥ 20%, and/or histologic grade 3). Patients received: three 21-day cycles of epirubicin/cyclophosphamide followed by eight 14-day cycles of nivolumab, triptorelin started concomitantly to chemotherapy, and exemestane started concomitantly to nivolumab. Primary endpoint was pathologic complete response (pCR; ypT0/is, ypN0).

RESULTS

A pCR was achieved by 7/43 patients [16.3%; 95% confidence interval (CI), 7.4-34.9]; the rate of residual cancer burden class 0-I was 25.6%. pCR rate was significantly higher for patients with PAM50 Basal breast cancer (4/8, 50%) as compared with other subtypes (LumA 9.1%; LumB 8.3%; P = 0.017). Tumor-infiltrating lymphocytes (TIL), immune-related gene-expression signatures, and specific immune cell subpopulations by multiplex immunofluorescence were significantly associated with pCR. A combined score of Basal subtype and TILs had an AUC of 0.95 (95% CI, 0.89-1.00) for pCR prediction. According to multiplex immunofluorescence, a switch to a more immune-activated tumor microenvironment occurred following exposure to anthracyclines. Most common grade ≥3 treatment-related adverse events (AE) during nivolumab were γ-glutamyltransferase (16.7%), alanine aminotransferase (16.7%), and aspartate aminotransferase (9.5%) increase. Most common immune-related AEs were endocrinopathies (all grades 1-2; including adrenal insufficiency, n = 1).

CONCLUSIONS

Luminal B-like breast cancers with a Basal molecular subtype and/or a state of immune activation may respond to sequential anthracyclines and anti-PD-1. Our data generate hypotheses that, if validated, could guide immunotherapy development in this context.

Circulating T-Cell Repertoires Correlate With the Tumor Response in Patients With Breast Cancer Receiving Neoadjuvant Chemotherapy

PURPOSE

Neoadjuvant chemotherapy (NAC) has been widely used in patients with breast cancer to minish tumor burden and increase resection rate of cancer. T-cell repertoire has been believed to be able to monitor antitumor immune responses. This study aimed to explore the dynamic change of T-cell repertoire and its clinical value in evaluating the tumor response in patients with breast cancer receiving NAC.

MATERIALS AND METHODS

Ninety-four patients who underwent NAC before surgery were recruited, and peripheral blood samples were collected at multiple time points during NAC. High-throughput T-cell receptor (TCR)-β sequencing was used to characterize the T-cell repertoire of every sample and analyzed the changes in circulating T-cell repertoire during NAC.

RESULTS

We found that the diversity of TCR repertoires was associated with age and clinical stage of the patients with breast cancer. The distribution of Vβ and Jβ genes in TCR repertoires was skewed in patients with human epidermal growth factor receptor 2-positive (HER2+) breast cancer. Vβ20.1 and Vβ30 expression levels before NAC correlate with tumor response after all cycles of NAC in HER2- and HER2+ patients, respectively. Some CDR3 motifs that correlated with clinical response in either HER2+ or HER2- patients were identified. Besides, TCR repertoire evolved during NAC and the diversity of TCR repertoire decreased more after two cycles of NAC in patients with good tumor response after all cycles of NAC (P = .0061).

CONCLUSION

Our results demonstrated that TCR repertoire correlated with the characteristics of the tumor, such as the expression status of HER2. Moreover, some characteristics of TCR repertoires that correlated with clinical response were identified and they might provide useful information to tailor therapeutic regimens at the early cycle of NAC.

Treatment with ribociclib shows favourable immunomodulatory effects in patients with hormone receptor-positive breast cancer-findings from the RIBECCA trial

BACKGROUND

Inhibitors of the cyclin-dependent kinases 4 and 6 (CDK4/6i) have significantly improved clinical outcomes in patients with advanced hormone receptor-positive (HR+) breast cancer and have demonstrated favourable antitumour immune responses in preclinical studies.

METHODS

Here, we investigated peripheral immune responses to ribociclib in patients with metastatic HR+ breast cancer as a preplanned exploratory subanalysis of the RIBECCA trial (NCT03096847). Peripheral blood mononuclear cells were subjected to immune cell profiling, gene expression analysis of immune-related signatures, and deep T cell receptor profiling before treatment started and after 12 weeks of treatment with ribociclib.

RESULTS

Gene expression analysis revealed an upregulation of signatures associated with an activated adaptive immune system and a decrease in immunosuppressive cytokine signalling during treatment with ribociclib. Profiling of peripheral immune cell subpopulations showed a decrease in Treg cell frequencies, which was associated with treatment response. Furthermore, induction of CD4+ naive T cells could be seen, whereas effector and memory T cell populations remained largely unchanged. Correspondingly, T cell repertoire diversity remained mostly unchanged during treatment, although an increase in clonality could be observed in single patients.

CONCLUSIONS

We show that treatment with ribociclib has significant effects on the peripheral innate and adaptive immune response in patients with HR+ breast cancer. Our data suggest that these effects lead to an activation of an already existing immune response rather than a de novo induction and make a strong case for future combination strategies of CDK4/6i with immunotherapies to enhance the adaptive immune response in HR+ breast cancer.

Intratumoral Heterogeneity and Immune Response Indicators to Predict Overall Survival in a Retrospective Study of HER2-Borderline (IHC 2+) Breast Cancer Patients

Breast cancer (BC) categorized as human epidermal growth factor receptor 2 (HER2) borderline [2+ by immunohistochemistry (IHC 2+)] presents challenges for the testing, frequently obscured by intratumoral heterogeneity (ITH). This leads to difficulties in therapy decisions. We aimed to establish prognostic models of overall survival (OS) of these patients, which take into account spatial aspects of ITH and tumor microenvironment by using hexagonal tiling analytics of digital image analysis (DIA). In particular, we assessed the prognostic value of Immunogradient indicators at the tumor–stroma interface zone (IZ) as a feature of antitumor immune response. Surgical excision samples stained for estrogen receptor (ER), progesterone receptor (PR), Ki67, HER2, and CD8 from 275 patients with HER2 IHC 2+ invasive ductal BC were used in the study. DIA outputs were subsampled by HexT for ITH quantification and tumor microenvironment extraction for Immunogradient indicators. Multiple Cox regression revealed HER2 membrane completeness (HER2 MC) (HR: 0.18, p = 0.0007), its spatial entropy (HR: 0.37, p = 0.0341), and ER contrast (HR: 0.21, p = 0.0449) as independent predictors of better OS, with worse OS predicted by pT status (HR: 6.04, p = 0.0014) in the HER2 non-amplified patients. In the HER2-amplified patients, HER2 MC contrast (HR: 0.35, p = 0.0367) and CEP17 copy number (HR: 0.19, p = 0.0035) were independent predictors of better OS along with worse OS predicted by pN status (HR: 4.75, p = 0.0018). In the non-amplified tumors, three Immunogradient indicators provided the independent prognostic value: CD8 density in the tumor aspect of the IZ and CD8 center of mass were associated with better OS (HR: 0.23, p = 0.0079 and 0.14, p = 0.0014, respectively), and CD8 density variance along the tumor edge predicted worse OS (HR: 9.45, p = 0.0002). Combining these three computational indicators of the CD8 cell spatial distribution within the tumor microenvironment augmented prognostic stratification of the patients. In the HER2-amplified group, CD8 cell density in the tumor aspect of the IZ was the only independent immune response feature to predict better OS (HR: 0.22, p = 0.0047). In conclusion, we present novel prognostic models, based on computational ITH and Immunogradient indicators of the IHC biomarkers, in HER2 IHC 2+ BC patients.

Preoperative Systemic Inflammatory Biomarkers Are Independent Predictors of Disease Recurrence in ER+ HER2- Early Breast Cancer

The host's immune system plays a crucial role in determining the clinical outcome of many cancers, including breast cancer. Peripheral blood neutrophils and lymphocytes counts may be surrogate markers of systemic inflammation and potentially reflect survival outcomes. The aim of the present study is to assess the role of preoperative systemic inflammatory biomarkers to predict local or distant relapse in breast cancer. In particular we investigated ER+ HER2- early breast cancer, considering its challenging risk stratification. A total of 1,763 breast cancer patients treated at tertiary referral Breast Unit were reviewed. Neutrophil-to-lymphocyte (NLR), platelet-to-lymphocyte (PLR) and lymphocyte-to-monocyte (LMR) ratios were assessed from the preoperative blood counts. Multivariate analyses for 5-years locoregional recurrence-free (LRRFS), distant metastases-free (DMFS) and disease-free survivals (DFS) were performed, taking into account both blood inflammatory biomarkers and clinical-pathological variables. Low NLR and high LMR were independent predictors of longer LRRFS, DMFS and DFS, and low PLR was predictive of better LRRFS and DMFS in the study population. In 999 ER+ HER2- early breast cancers, high PLR was predictive of worse LRRFS (HR 0.42, p=0.009), while high LMR was predictive of improved LRRFS (HR 2.20, p=0.02) and DFS (HR 2.10, p=0.01). NLR was not an independent factor of 5-years survival in this patients' subset. Inflammatory blood biomarkers and current clinical assessment of the disease were not in agreement in terms of estimate of relapse risk (K-Cohen from -0.03 to 0.02). In conclusion, preoperative lymphocyte ratios, in particular PLR and LMR, showed prognostic relevance in ER+ HER2- early breast cancer. Therefore, they may be used in risk stratification and therapy escalation/de-escalation in patients with this type of tumor.

Enriched transcriptome analysis of laser capture microdissected populations of single cells to investigate intracellular heterogeneity in immunostained FFPE sections

To investigate intracellular heterogeneity, cell capture of particular cell populations followed by transcriptome analysis has been highly effective in freshly isolated tissues. However, this approach has been quite challenging in immunostained formalin-fixed paraffin-embedded (FFPE) sections. This study aimed at combining the standard pathology techniques, immunostaining and laser capture microdissection, with whole RNA-sequencing and bioinformatics analysis to characterize FFPE breast cancer cell populations with heterogeneous expression of progesterone receptor (PR). Immunocytochemical analysis revealed that 60% of MCF-7 cells admixture highly express PR. Immunocytochemistry-based targeted RNA-seq (ICC-RNAseq) and in silico functional analysis revealed that the PR-high cell population is associated with upregulation in transcripts implicated in immunomodulatory and inflammatory pathways (e.g. NF-κB and interferon signaling). In contrast, the PR-low cell population is associated with upregulation of genes involved in metabolism and mitochondrial processes as well as EGFR and MAPK signaling. These findings were cross-validated and confirmed in FACS-sorted PR high and PR-low MCF-7 cells and in MDA-MB-231 cells ectopically overexpressing PR. Significantly, ICC-RNAseq could be extended to analyze samples captured at specific spatio-temporal states to investigate gene expression profiles using diverse biomarkers. This would also facilitate our understanding of cell population-specific molecular events driving cancer and potentially other diseases.

A review of immune checkpoint blockade in breast cancer

In the recent years characterized by the cancer immunotherapy revolution, attention has turned to how to potentially boost and/or generate an efficient anti-tumor immune response in breast cancer (BC). Clinical activity of immune checkpoint blockade (ICB) targeting PD-1 or PD-L1 in BC has been more evident in the triple negative subtype and in earlier lines of the treatment. Remarkably, some responders to single agent ICB have achieved durable responses with metastatic disease, possibly as a result of treatment-induced immunological memory. However, most BC are immunologically quiescent and current research efforts developing ICB combinations are attempting to convert "cold" into "hot" tumors by manipulating the tumor microenvironment, expanding anti-tumor T cells improving efficient antigen presentation, and suppressing pro-tumor inhibitory cells. The aim of this review is to summarize existing data on the efficacy of immune checkpoint blockers as single agents and combination strategies in all BC subtypes, highlighting the BC subgroups that benefit most from ICB.

Neu Perspectives, Therapies, and Challenges for Metastatic HER2-Positive Breast Cancer

Even though gene amplification or protein overexpression occurs in approximately one-fifth of all breast cancers, the discovery of HER2 has, nevertheless, had profound implications for the disease. Indeed, the characterization of the receptor resulted in a number of significant advances. Structurally, unique features provided avenues for the development of numerous compounds with target-specificity; molecularly, biological constructs revealed a highly complex, internal signal transduction pathway with regulatory effects on tumor proliferation, survival, and perhaps, even resistance; and clinically, disease outcomes manifested its predictive and prognostic value. Yet despite the receptor’s utility, the beneficial effects are diminished by tumor recurrence after neo- or adjuvant therapy as well as losses resulting from the inability to cure patients with metastatic disease. What these observations suggest is that while tumor response may be partially linked to uncoupling cell surface message reception and nuclear gene expression, as well as recruitment of the innate immune system, disease progression and/or resistance may involve a reprogrammable signaling mainframe that elicits alternative growth and survival signals. This review attempts to meld current perceptions related to HER2-positive metastatic breast cancer with particular attention to current biological insights and therapeutic challenges.

Endogenous and Therapeutic Estrogens: Maestro Conductors of the Microenvironment of ER+ Breast Cancers

Estrogen receptor alpha (ERα) marks heterogeneous breast cancers which display a repertoire of somatic genomic mutations and an immune environment that differs from other breast cancer subtypes. These cancers also exhibit distinct biological behaviors; despite an overall better prognosis than HER2+ or triple negative breast cancers, disseminated dormant cells can lead to disease recurrence decades after the initial diagnosis and treatment. Estrogen is the best studied driver of these cancers, and antagonism or reduction of estrogen activity is the cornerstone of therapeutic approaches. In addition to reducing proliferation of ERα+ cancer cells, these treatments also alter signals to multiple other target cells in the environment, including immune cell subpopulations, cancer-associated fibroblasts, and endothelial cells via several distinct estrogen receptors. In this review, we update progress in our understanding of the stromal cells populating the microenvironments of primary and metastatic ER+ tumors, the effects of estrogen on tumor and stromal cells to modulate immune activity and the extracellular matrix, and net outcomes in experimental and clinical studies. We highlight new approaches that will illuminate the unique biology of these cancers, provide the foundation for developing new treatment and prevention strategies, and reduce mortality of this disease.

Comprehensive description of the current breast cancer microenvironment advancements via single-cell analysis

Breast cancer is a heterogeneous disease with a complex microenvironment consisting of tumor cells, immune cells, fibroblasts and vascular cells. These cancer-associated cells shape the tumor microenvironment (TME) and influence the progression of breast cancer and the therapeutic responses in patients. The exact composition of the intra-tumoral cells is mixed as the highly heterogeneous and dynamic nature of the TME. Recent advances in single-cell technologies such as single-cell DNA sequencing (scDNA-seq), single-cell RNA sequencing (scRNA-seq) and mass cytometry have provided new insights into the phenotypic and functional diversity of tumor-infiltrating cells in breast cancer. In this review, we have outlined the recent progress in single-cell characterization of breast tumor ecosystems, and summarized the phenotypic diversity of intra-tumoral cells and their potential prognostic relevance.

Immunotherapy for the Breast Cancer treatment: Current Evidence and Therapeutic Options

Breast cancer (BC) stands at the first position among all forms of malignancies found in women globally. The available therapeutic approaches for breast cancer includes chemotherapy, radiation therapy, hormonal therapy and finally surgery. Despite the conventional therapies, in recent years the advance immunology based therapeutics emerge a potential in breast cancer treatment, including immune checkpoint blockades, vaccines and in combination with other treatment strategies. Although, commonly used treatments like trastuzumab/pertuzumab for human epidermal growth factor receptor 2 (Her2) positive and hormone therapy for estrogen receptor (ER) positive and/or progesterone receptor (PR) positive BC are specific but triple negative breast cancer (TNBC) cases remain a great challenge for treatment measures. Immune checkpoint inhibitors (anti-PD-1/ anti-CTLA-4) and anti-cancer vaccines (NeuVax, Muc-1, AVX901, INO-1400 and CEA), either alone or in combination with other therapies have created new paradigm in therapeutic world. In this review, we highlighted the current immunotherapeutic aspects and their ongoing trials towards the better treatment regimen for BC.

The Peripheral Immune Landscape of Breast Cancer: Clinical Findings and In Vitro Models for Biomarker Discovery

Breast cancer is the deadliest female malignancy worldwide and, while much is known about phenotype and function of infiltrating immune cells, the same attention has not been paid to the peripheral immune compartment of breast cancer patients. To obtain faster, cheaper, and more precise monitoring of patients' status, it is crucial to define and analyze circulating immune profiles. This review compiles and summarizes the disperse knowledge on the peripheral immune profile of breast cancer patients, how it departs from healthy individuals and how it changes with disease progression. We propose this data to be used as a starting point for validation of clinically relevant biomarkers of disease progression and therapy response, which warrants more thorough investigation in patient cohorts of specific breast cancer subtypes. Relevant clinical findings may also be explored experimentally using advanced 3D cellular models of human cancer-immune system interactions, which are under intensive development. We review the latest findings and discuss the strengths and limitations of such models, as well as the future perspectives. Together, the scientific advancement of peripheral biomarker discovery and cancer-immune crosstalk in breast cancer will be instrumental to uncover molecular mechanisms and putative biomarkers and drug targets in an all-human setting.

Single-Cell Profiling to Explore Immunological Heterogeneity of Tumor Microenvironment in Breast Cancer

Immune infiltrates in the tumor microenvironment (TME) of breast cancer (BRCA) have been shown to play a critical role in tumorigenesis, progression, invasion, and therapy resistance, and thereby will affect the clinical outcomes of BRCA patients. However, a wide range of intratumoral heterogeneity shaped by the tumor cells and immune cells in the surrounding microenvironment is a major obstacle in understanding and treating BRCA. Recent progress in single-cell technologies such as single-cell RNA sequencing (scRNA-seq), mass cytometry, and digital spatial profiling has enabled the detailed characterization of intratumoral immune cells and vastly improved our understanding of less-defined cell subsets in the tumor immune environment. By measuring transcriptomes or proteomics at the single-cell level, it provides an unprecedented view of the cellular architecture consist of phenotypical and functional diversities of tumor-infiltrating immune cells. In this review, we focus on landmark studies of single-cell profiling of immunological heterogeneity in the TME, and discuss its clinical applications, translational outlook, and limitations in breast cancer studies.

Identification of unanimous immune subtypes for different hormone receptor phenotypes of human breast cancer with potential prognostic significance

The immunogenicity of the breast tumor microenvironment is clinically heterogeneous. The insight into the role of tumor-infiltrating lymphocytes (TILs) might serve as a biomarker to predict a survival benefit and enable optimal patient selection for immunotherapy. In this study, we aimed at characterizing the breast cancer immune subtypes linked to CD8 T cells and associating with the patient characteristics and clinical outcomes. We analyzed the immune gene signatures of human breast cancer using The Genotype-Tissue Expression (GTEx) and The Cancer Genome Atlas (TCGA) database profiling of 1092 breast tumor patients. We performed hierarchical clustering to the immune gene expression by applying hormone receptor status including triple negative breast cancer to categorize 66 immune-related genes in breast tumors. The separation was characterized by dividing the breast tumors into two major immune subtypes: predominant immune (PI) subtype and low immune subtype (LI). Our results showed that both PI and LI subtypes can be observed in the different hormone receptor phenotypes of breast tumors, and PI subtype accounted for 16% and LI subtype 20% in the breast tumor patients. The estimated odds for LI subtype breast tumors were significantly higher than PI subtype breast tumors in primary tumor stages. Our data demonstrated that the PI subtype breast tumors have significantly improved survival compared with LI subtype. Our findings provide a novel perspective of breast cancer immune subtypes linked to CD8 T cells. The immune subtypes will be a valuable resource for future research to identify clinically relevant biomarkers for precision immunotherapy.

Immune microenvironment and intrinsic subtyping in hormone receptor-positive/HER2-negative breast cancer

Little is known regarding the interaction between immune microenvironment and tumor biology in hormone receptor (HR)+/HER2− breast cancer (BC). We here assess pretreatment gene-expression data from 66 HR+/HER2− early BCs from the LETLOB trial and show that non-luminal tumors (HER2-enriched, Basal-like) present higher tumor-infiltrating lymphocyte levels than luminal tumors. Moreover, significant differences in immune infiltrate composition, assessed by CIBERSORT, were observed: non-luminal tumors showed a more proinflammatory antitumor immune infiltrate composition than luminal ones.

Immune Infiltrates in Breast Cancer: Recent Updates and Clinical Implications

In recent decades, the increasing interest in the field of immunotherapy has fostered an intense investigation of the breast cancer (BC) immune microenvironment. In this context, tumor-infiltrating lymphocytes (TILs) have emerged as a clinically relevant and highly reproducible biomarker capable of affecting BC prognosis and response to treatment. Indeed, the evaluation of TILs on primary tumors proved to be strongly prognostic in triple-negative (TN) BC patients treated with either adjuvant or neoadjuvant chemotherapy, as well as in early TNBC patients not receiving any systemic treatment, thus gaining level-1b evidence in this setting. In addition, a strong relationship between TILs and pathologic complete response after neoadjuvant chemotherapy has been reported in all BC subtypes and the prognostic role of higher TILs in early HER2-positive breast cancer patients has also been demonstrated. The interest in BC immune infiltrates has been further fueled by the introduction of the first immune checkpoint inhibitors in the treatment armamentarium of advanced TNBC in patients with PD-L1-positive status by FDA-approved assays. However, despite these advances, a biomarker capable of reliably and exhaustively predicting immunotherapy benefit in BC is still lacking, highlighting the imperative need to further deepen this issue. Finally, more comprehensive evaluation of immune infiltrates integrating both the quantity and quality of tumor-infiltrating immune cells and incorporation of TILs in composite scores encompassing other clinically or biologically relevant biomarkers, as well as the adoption of software-based and/or machine learning platforms for a more comprehensive characterization of BC immune infiltrates, are emerging as promising strategies potentially capable of optimizing patient selection and stratification in the research field. In the present review, we summarize available evidence and recent updates on immune infiltrates in BC, focusing on current clinical applications, potential clinical implications and major unresolved issues.

An overview of immune checkpoint inhibitors in breast cancer

Although breast cancer is not traditionally considered an immunogenic type of tumor, the combination of immunotherapy and chemotherapy has recently emerged as a novel treatment option in triple-negative subtype in the advanced setting and other similar combinations of immune checkpoint inhibitors with chemotherapy are expected to become part of the neoadjuvant management in the near future. In addition, encouraging results have been observed with the combination of immune checkpoint blockade with diverse biological agents, including anti-HER2 agents, CDK 4/6 inhibitors, PARP-inhibitors. The present review summarized the available evidence coming from clinical trials on the role of immune checkpoint inhibitors in the management of breast cancer, both in advanced and early setting.

Peripheral cytotoxic T lymphocyte predicts first-line progression free survival in HER2-positive advanced breast cancer

Background

The role of peripheral blood lymphocyte (pBL) in breast cancer has long been studied. However, the predictive role of pBL in advanced breast cancer (ABC) is poorly understood.

Methods

A total of 303 patients with ABC were consecutively recruited at our center between January 2015 and September 2019. At baseline, pBL subtypes were detected in all patients with 229 blood samples available for circulating tumor DNA (ctDNA) detection. pBL was analyzed through flow cytometry. ctDNA-based gene mutations were detected using next generation sequencing. The cutoff value of pCTL was estimated by X-tile software. Progression free survival (PFS) was estimated by Kaplan-Meier curve and Cox hazard proportion regression model, with difference detection by log-rank test.

Results

Median follow-up time of the study was 21.0 months. The median age of diagnosis was 52.0 years. Among the pBL subtypes, only pCTL level was found predictive for PFS in the HER2+ patients whom received anti-HER2 therapy (13.1 vs. 5.6 months, P = 0.001). However, the predictive role of pCTL was not found in HR-positive (P = 0.716) and TNBC (P = 0.202). pCTL high associated with suppressive immune indictors including lower CD4/CD8 ratio (P = 0.004) and high level of Treg cell (P = 0.004). High occurrence of FGFR1 amplification which has been reported as immune suppressor was also found in HER2+ patients with pCTL high (22.2% vs. 4.3%, P = 0.048).

Conclusions

Higher pCTLs level associated with shorter PFS and FGFR1 mutation in HER2+ ABC patients.

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High pCTL level predicts shorter first-line PFS in HER2+ patients receiving anti-HER2 based regimens.

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The predictive role of pCTL level found in HER2+ patients was not applicable in HR+ and TNBC patients.

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High level of pCTL was associated with immunosuppressive status and FGFR1 mutations in HER2+ breast cancer patients.

Therapeutic Strategies for the Management of Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Positive (HR+/HER2+) Breast Cancer: A Review of the Current Literature

Enormous advances have been made in the understanding and treatment of human epidermal growth factor receptor 2-positive breast cancer (HER2+ BC) in the last 30 years that have resulted in survival gains for affected patients. A growing body of evidence suggests that hormone receptor-positive (HR+)/HER2+ BC and HR-negative (HR-)/HER2+ BC are biologically different, with complex molecular bidirectional crosstalk between the estrogen receptor and HER2 pathway potentially affecting sensitivity to both HER2-targeted and endocrine therapy in patients with HR+/HER2+ BC. Subgroup analyses from trials enrolling patients with HER2+ BC and the results of clinical trials specifically designed to evaluate therapy in patients with HR+/HER2+ BC are helping to guide treatment decisions. In this context, encouraging results with strategies aimed at delaying or reversing drug resistance, including extended adjuvant therapy and the addition of drugs targeting alternative pathways, such as cyclin-dependent kinase (CDK) 4 and 6 inhibitors, have recently emerged. We have reached the point where tailoring the treatment according to risk and biology has become the paradigm in early BC. However, further clinical trials are needed that integrate translational research principles and identify and consider specific patient subgroups and biomarkers.

Tumour-Infiltrating Inflammatory Cells in Early Breast Cancer: An Underrated Prognostic and Predictive Factor?

The role of tumour-infiltrating inflammatory cells (TIICs) in the disease progression of hormone-receptor-positive breast cancer (HR+ BC) is largely unclear since it is generally regarded as the least immunogenic BC subtype. This study investigated the prognostic significance of CD1a+ dendritic cells, CD20+ B cells, CD45RO+ memory T cells and CD4+ T-helper cells in HR+ BC. One hundred and forty-six patients were treated for early stage, distant-metastases-free HR+ BC in an accelerated partial breast irradiation (APBI) phase II trial. Immunohistochemistry was used to double-stain two adjoining sets of tissue microarrays from pre-RT (radiotherapy) tumour resection samples for CD1a/CD20 and CD45RO/CD4. Cell densities of CD1a+, CD20+, CD45RO+ and CD4+ TIICs in the stromal and intraepithelial compartment were registered semiautomatically. High densities of CD20+ and CD4+ TIICs were strongly associated with reduced disease-free survival (DFS), while high stromal CD45RO+ TIIC densities were indicators of subsequent successful treatment. An immunoscore based on CD20+ and CD45RO+ TIIC densities identified three different risk groups (p < 0.001). Thus, contrary to current assumptions, intratumoural immune cell composition might be an important prognostic indicator and a possible contributing factor in the outcome of HR+ BC and should be the subject of further research. Specifically, B-cell infiltration entailed an increased relapse rate and could play an important role in disease progression.

A Spontaneous Aggressive ERα+ Mammary Tumor Model Is Driven by Kras Activation

The NRL-PRL murine model, defined by mammary-selective transgenic rat prolactin ligand rPrl expression, establishes spontaneous ER+ mammary tumors in nulliparous females, mimicking the association between elevated prolactin (PRL) and risk for development of ER+ breast cancer in postmenopausal women. Whole-genome and exome sequencing in a discovery cohort (n = 5) of end-stage tumors revealed canonical activating mutations and copy number amplifications of Kras. The frequent mutations in this pathway were validated in an extension cohort, identifying activating Ras alterations in 79% of tumors (23 of 29). Transcriptome analyses over the course of oncogenesis revealed marked alterations associated with Ras activity in established tumors compared with preneoplastic tissues; in cell-intrinsic processes associated with mitosis, cell adhesion, and invasion; as well as in the surrounding tumor environment. These genomic analyses suggest that PRL induces a selective bottleneck for spontaneous Ras-driven tumors that may model a subset of aggressive clinical ER+ breast cancers.

Tumor-infiltrating lymphocytes (TILs) in ER+/HER2- breast cancer

PURPOSE

The prognostic role of tumor-infiltrating lymphocytes (TILs) in ER+/HER2- breast cancer (BC) is debated. We evaluated the association of TILs and clinico-pathological features with distant disease-free survival (DDFS) in patients with ER+/HER2- BC treated at a single institution.

PATIENTS AND METHODS

A mono-institutional case-cohort series of 987 patients with early ER+/HER2- BC was retrospectively analyzed. TILs were considered both as continuous variable, and dichotomized in low (< 5%) vs high (≥ 5%). The main outcome was DDFS. Median follow-up was 7.5 years (0.1-10). Univariate and multivariable Cox proportional hazards regression with inverse sub-cohort sampling probability weighting were used to evaluate the risk across groups.

RESULTS

Median TIL count was 2% (Q1-Q3 1-4%). Higher TILs were positively associated with number of lymph nodes involved (p = 0.003), tumor grade (p < 0.0001), peritumoral vascular invasion (p = 0.003), higher Ki-67 (p = 0.0001), luminal B subtype (p < 0.0001), and chemotherapy use (p < 0.00019). In multivariable regression analysis, only higher Ki-67 expression retained significant association with TILs. At univariate Cox regression analysis, TIL expression (≥ 5% vs. < 5%) was not associated with DDFS (HR 1.08, 95% CI 0.80-1.46, p = 0.62). In patients treated with adjuvant chemotherapy, high TILs were associated with better DDFS (HR 0.52, 95%CI 0.33-0.83, p = 0.006), particularly in the group with Ki-67 ≥ 20% (HR 0.50, 95%CI 0.29-0.86, p = 0.01).

CONCLUSION

High TILs in ER+/HER2- BC are significantly associated with clinico-pathological features of dismal outcome. TIL prognostic value seems different in patients treated with or without chemotherapy. Our findings suggest that the high-risk subgroup might be more immunogenic, thus deserving the exploration of immunotherapy approaches.

Immune checkpoint inhibitors: Key trials and an emerging role in breast cancer

This review focuses on immune checkpoint inhibitors - immunomodulatory agents that aim to relieve tumour-mediated immune-cell suppression. Immune checkpoint proteins can be expressed on the tumour-cell or immune-cell populations. Immune checkpoint proteins dampen the immune response by inactivating immune cells capable of tumour destruction. Blockade of immune checkpoints has shown impressive results in a range of solid cancers, particularly melanoma and non-small cell lung cancer. The potential benefit of this class of drugs is widespread across most cancer types and an unprecedented number of clinical studies are underway to examine the benefit of these agents. The aims of this review are to: provide an overview of the key early immune checkpoint inhibitor trials involving drugs targeting programmed cell death-1 (PD-1), programmed cell death ligand-1 (PD-L1) and cytotoxic T-lymphocyte antigen-4 (CTLA-4) in multiple disease types; provide an overview of emerging therapies aimed at these targets; and provide a detailed exploration of the status of immune checkpoint inhibitors in breast cancer.

Blockade of PD-1, PD-L1, and TIM-3 Altered Distinct Immune- and Cancer-Related Signaling Pathways in the Transcriptome of Human Breast Cancer Explants

Immune checkpoint inhibitors (ICIs) are yet to have a major advantage over conventional therapies, as only a fraction of patients benefit from the currently approved ICIs and their response rates remain low. We investigated the effects of different ICIs—anti-programmed cell death protein 1 (PD-1), anti-programmed death ligand-1 (PD-L1), and anti-T cell immunoglobulin and mucin-domain containing-3 (TIM-3)—on human primary breast cancer explant cultures using RNA-Seq. Transcriptomic data revealed that PD-1, PD-L1, and TIM-3 blockade follow unique mechanisms by upregulating or downregulating distinct pathways, but they collectively enhance immune responses and suppress cancer-related pathways to exert anti-tumorigenic effects. We also found that these ICIs upregulated the expression of other IC genes, suggesting that blocking one IC can upregulate alternative ICs, potentially giving rise to compensatory mechanisms by which tumor cells evade anti-tumor immunity. Overall, the transcriptomic data revealed some unique mechanisms of the action of monoclonal antibodies (mAbs) targeting PD-1, PD-L1, and TIM-3 in human breast cancer explants. However, further investigations and functional studies are warranted to validate these findings.

Clinicopathologic Characteristics of Breast Cancer According to the Infiltrating Immune Cell Subtypes

The clinical significance of immune cell subtypes in breast cancer remains poorly understood. To identify tumor-infiltrating immune cell subtypes in breast cancer and investigate their implications, tissue microarrays were constructed using 334 cases of invasive ductal carcinoma (luminal A type: 162 (48.5%), luminal B type: 96 (28.7%), HER-2 type: 21 (6.3%), and triple negative breast cancer: 55 (16.5%)). Hormone receptors (ER, PR, and HER-2), Ki-67, and immune cell subtype-related proteins (STAT4, STAT6, FOXP3, CD8, CD68, and CD163) were assessed immunohistochemically. The proportion of highly expressed STAT6, FOXP3, CD8, CD68, and CD163 proteins was found to be lowest in luminal A type but highest in the HER-2 type. Additionally, high-level STAT6, FOXP3, CD68, and CD163 protein expression was associated with higher histologic grade. ER negativity was associated with high STAT6, FOXP3, and CD163 expression levels, whereas PR negativity and high Ki-67 labeling index were associated with high CD163 expression. Univariate (p = 0.003) and multivariate Cox (hazard ratio: 2.435, 95% CI: 1.110-5.344, p = 0.049) analyses showed that high CD8 expression is an independent factor associated with shorter disease-free survival. Immune cell subtype-related protein expression is dependent on breast cancer molecular subtypes, and CD8 expression is associated with patient prognosis.

High Expression of microRNA-143 is Associated with Favorable Tumor Immune Microenvironment and Better Survival in Estrogen Receptor Positive Breast Cancer

microRNA-143 (miR-143) is a well-known tumor suppressive microRNA that exhibits anti-tumoral function by targeting KRAS signaling pathways in various malignancies. We hypothesized that miR-143 suppresses breast cancer progression by targeting KRAS and its effector molecules. We further hypothesized that high expression of miR-143 is associated with a favorable tumor immune microenvironment of estrogen receptor (ER)-positive breast cancer patients which result in improved survival. Two major publicly available breast cancer cohorts; The Cancer Genome Atlas (TCGA) and Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) were used. The miR-143 high expression group was associated with increased infiltration of anti-cancer immune cells and decreased pro-cancer immune cells, as well as enrichment of the genes relating to T helper (Th1) cells resulting in improved overall survival (OS) in ER-positive breast cancer patients. To the best of our knowledge, this is the first study to demonstrate that high expression of miR-143 in cancer cells associates with a favorable tumor immune microenvironment, upregulation of anti-cancer immune cells, and suppression of the pro-cancer immune cells, associating with better survival of the breast cancer patients.

Cortical Brain Age from Pre-treatment to Post-chemotherapy in Patients with Breast Cancer

Chemotherapy-related cognitive impairment and associated brain changes may reflect accelerated brain aging; however, empirical evidence for this theory is limited. The purpose of this study was to measure brain aging in newly diagnosed patients with breast cancer treated with chemotherapy (n = 43) and compare its longitudinal change to that of controls (n = 50). Brain age indices, derived from cortical measures, were compared between women with breast cancer and matched healthy controls across 3 timepoints (time 1: pre-surgery, time 2: 1 month following chemotherapy completion, and time 3: 1-year post-chemotherapy). The breast cancer group showed a significant decrease in cortical thickness across the 3 timepoints (p < .001) and a trend towards significant increase in predicted brain age especially from pre-treatment (time 1) to post-chemotherapy (time 2) compared to controls (p = 0.08). Greater increase in predicted brain age was related to several clinical factors (HER-2 status, surgery type, and history of neoadjuvant chemotherapy) and greater decrease in cortical thickness was associated with greater decrease in performance on a verbal learning task from time 1 to time 3 (r = - 0.48, p < .01). This study demonstrated evidence of increased cortical brain aging in middle-aged patients with breast cancer following chemotherapy treatment that was associated with decreased verbal memory performance.