Background
Luminal breast cancer (BC) is characterized by a positive estrogen receptor (ER) status and categorized into two subclasses, A and B [
1]. Luminal B BC has a higher tumor cell proliferation rate than luminal A BC, with a breast cancer-specific mortality rate twice as high [
1]. The rates of pathological complete response (pCR) with neo-adjuvant chemotherapy (NACT), are poor for luminal B compared to the non-luminal subtypes: 15% in luminal B versus 46% in HER2 positive BC and 45% in triple negative BC (TNBC) [
2‐
4]. Luminal B BC patients who don not achieve pCR after NACT have a significantly lower event-free survival, revealing a need to increase response rate to NACT for luminal B BC [
5].
Recent developments in immuno-oncology permit classification of tumours according to their immunological contexture: inflamed cancer types, such as melanoma and lung cancer, are characterized by the presence of tumour infiltrating lymphocytes (TILs), high CD8+ T-cell density, and high programmed cell death receptor ligand 1 (PD-L1) positivity of tumour or immune cells, and immune signatures. Because of this, higher overall long-term outcomes with immunotherapy can be attained in inflamed cancer types [
6,
7], whereas in non-inflamed cancer types, such as a large proportion of luminal B BC, results with isolated PD-1/PD-L1 blockade are disappointing. Hence, strategies to prime immune responses seem critical to increase clinical benefit of immunotherapy in non-inflamed cancer types [
8‐
10]. An area of active research is how to convert non-inflamed cancers into inflamed cancers, leveraging the effects of local and/or systemic treatment and increasing pCR rates with immunotherapy combinations.
The priming of an anti-tumour immune response in early luminal B BC could be attained via a myriad of strategies [
11]. In the Neo-CheckRay trial, three priming strategies are used: 1. chemotherapy (given in the three study arms), 2. radiation therapy to the primary BC (given in the three study arms) and 3. blockade of the adenosine pathway (only given in arm 3). The rationale behind these priming strategies will be addressed in the discussion section of the present manuscript.
Discussion
Approximately 40% of patients with early-stage luminal B BC who receive NACT experience recurrent disease within 5 years [
5], therefore new treatment strategies to decrease recurrence rates are greatly needed. In recent years, an emerging treatment strategy is the use of ICB. Early trials of single-agent ICB in BC show evidence of a modest response, less than in some other cancers due to the low baseline immunogenicity of most BCs [
17]. Recent advances in the field of immunogenomics identified different immune subtypes that are hypothesized to define how immune response patterns impact prognosis [
18]. In BC, the immune response of hormone receptor positive (luminal) BC is lower compared to the TNBC and HER2+ subtypes, assumedly because luminal BC is generally less inflamed, characterized by a lower presence of TILs and lower PD-L1 expression [
19]. In TNBC and HER2+ BC, increased TIL concentration is correlated with response to chemotherapy and immunotherapy, and is associated with increased survival, whereas in luminal BC the prognostic and predictive value of increased TIL concentration is not fully established [
7].
An attractive strategy to increase the benefit of immunotherapy in luminal B BC seems to be to prime the immune response using a combination strategy with chemotherapy, a doublet immunotherapy, radiation therapy or other agents. The I-SPY2 trial investigated the addition of pembrolizumab (anti PD-1) to a standard NACT backbone in TNBC and luminal B BCs [
20]. The addition of pembrolizumab increased pCR rates from 13 to 30% in luminal B BC and from 22 to 60% in TNBC. These results indicate that non-inflamed” tumours might benefit from immunotherapy when combined with other treatments, such as chemotherapy. In TNBC, the phase III trial KEYNOTE 522 demonstrated superiority of the pembrolizumab-NACT combination with 64.8% pCR and 51.2% pCR in the NACT-only group [
21], whereas for luminal B BC, KEYNOTE 756 is ongoing.
An active domain of research is the identification of non-chemotherapeutic agents able to prime the immune response and to further enhance the conversion to more inflamed tumours with the hope of increasing response rates to immunotherapy. In the Neo-CheckRay trial, radiation therapy to the primary tumour and the use of an anti-CD-73 are investigated as potential strategies to increase the response rate following immunotherapy-chemotherapy combinations.
In recent years, a large amount of clinical trials and animal studies have described the synergistic effects on local and distant tumour control of combining radiation therapy with immunotherapy [
22‐
26]. In BC models, radiation has been shown to induce T cell priming via antigenic release and by activation of the innate immunity [
22,
27,
28]. Pivotal pre-clinical work by Vanpouille-Box et al. showed that a fractionation schedule of three fractions of 8 Gy given daily induces a better activation of the cGAS-STING pathway in comparison to treatments with a higher dose per fraction [
29]. Despite the fact that the 3 × 8 Gy schedule has been used in several clinical trials to evaluate its efficacy and toxicity in combination with immunotherapy [
30‐
32], this fractionation schedule remains yet to be validated. While an excessively high radiation fraction dose might suppress the immune response or increase toxicity, an insufficient dose might not induce an immune response at all. Apart from dose/fractionation parameters, also the sequencing of radiation therapy when combined with ICB remains largely unknown, further highlighting the importance of the need for more clinical trials. A challenge of delivering pre-operative radiation therapy in combination with immunotherapy is the concern of post-operative toxicities, with potential impacts on breast cosmesis, lymphedema, fibrosis and surgical outcomes, especially in case of breast reconstruction. The impact on these parameters can be estimated from other pre-operative trials combing radiation therapy with chemotherapy [
33], but it remains unknown how the addition of immunotherapy will modulate these effects. For this, breast cosmesis will be monitored during and after the Neo-Checkray trial, using standardised breast photography and clinical examinations.
Oleclumab is a human immunoglobulin monoclonal antibody (mAb) that selectively binds to and inhibits the ectonucleotidase activity of CD73. CD73 converts adenosine monophosphate (AMP) into adenosine. Adenosine presents anti-inflammatory and immunosuppressive effects, mediated by the adenosine receptors expressed on immune cells [
34,
35]. CD73 therefore serves as an immune checkpoint, with the clinical association between elevated CD73 expression and poor prognosis being well documented in several tumour types [
36‐
38]. The therapeutic potential of blocking adenosine pathways with monoclonal antibodies targeting is currently being tested in phase II trials [
39].
Radiation therapy has pre-clinically been shown to act synergistically with anti-CD-73 through the prevention of adenosine-mediated immunosuppression [
40]. Recent research suggests that CD73 may be a radiation-induced checkpoint, and that CD73 blockade in combination with radiation therapy and ICB might improve patient response to therapy [
41]. Pre-clinical data show that the combination of CD73 inhibition and radiation therapy has the following effect: 1) enhancement of the radiation-induced activation of the antitumour immune response, 2) restriction of the immunosuppressive action of CD39/CD73 on circulating immune cells and 3) attenuation of adverse late effects of radiation therapy through inhibition of fibrosis [
41‐
43].
The Neo-CheckRay trial was designed to harness these potential synergies, by combining durvalumab with oleclumab and radiation therapy to the primary BC in addition to a standard chemotherapy backbone. Parts of this combination have been tested for safety, such as the combination of radiation therapy and docetaxel [
33], radiation therapy with PD-L1 blockade [
32], and the combination of oleclumab, durvalumab and paclitaxel [
44]. The combination of all 4 treatment agents will be tested in a safety run-in phase of the Neo-CheckRay trial before proceeding to the randomized phase II trial.
Given the choice of RCB 0–1 as primary endpoint of the current trial, it was decided to deliver radiation therapy to the three treatment arms to avoid an imbalance in local treatment between the study arms. Indeed, radiation therapy might increase the local response without necessarily reflecting an impact on the systemic response and is therefore more difficult to discriminate as being an independent surrogate of long-term outcome. Moreover, our study design allows singling out the effect of durvalumab and oleclumab without the results being disbalanced by radiation therapy. The drawback of this choice is that arm 1 is not a commonly accepted standard of care, which would have been chemotherapy alone, excluding the individual impact of pre-operative SBRT.
A similar trial could have been designed with the systemic treatments in the adjuvant setting or in the metastatic setting. The neo-adjuvant setting, however, with a primary tumour in place, presents unique advantages for priming the anti-tumour immune response and potential eradication of micrometastatic disease [
45]. Pre-clinical models of BC support the superiority of neo-adjuvant immunotherapy compared to adjuvant immunotherapy [
46]. With the intact primary cancer still in place, radiation therapy and ICB might help to convert the tumour into an in-situ, individualized vaccine; hypothetically preventing patients against metastasis [
47]. In addition, neo-adjuvant treatment followed by complete surgical resection of the tumour allows a rapid and thorough assessment of response with the possibility of performing a wide range of translational research on the surgical specimen.
The Neo-Checkray trial targets a subselection of luminal B cancers by strictly including patients with a MammaPrint test showing a genomic high risk of relapse. Patients with luminal B BC and a genomic high risk of relapse derive a greater benefit from chemotherapy than patients with a genomic low risk result [
48]. The use of this test ensures that patients included in the trial derive benefit of chemotherapy. Unlike with chemotherapy, biomarkers to select patients for immunotherapy have not yet been identified for BC patients. Hence, an important part of the translational research objectives of the Neo-CheckRay study is to evaluate the predictive value of potential biomarkers, such as PD-L1 and TILs, and to identify other biomarkers, both in situ as well as in the systemic circulation [
49], that might help to better tailor therapy in this setting.
Few other trials are investigating the role of pre-operative radiation therapy in combination with immunotherapy in BC. A phase I clinical trial (NCT03366844 - recruiting) is evaluating the safety of 3 × 8 Gy radiation therapy to the primary BC in combination with pembrolizumab for TNBC and ER + HER2- BC, without the use of chemotherapy [
50]. Another pre-operative design in luminal BC is the CBCV trial (NCT03804944 – not yet recruiting), a 4 arms study consisting of 1) radiation therapy 3 × 8 Gy (RT) + hormonal treatment (HT); 2) RT/HT + pembrolizumab; 3) RT/HT + CDX-301 (anti-CD135); 4) RT/HT + pembrolizumab + CDX-301 [
51]. In TNBC, the PANDoRA trial (NCT03872505 – not yet recruiting) will evaluate the addition of radiation therapy (3x8Gy) to non-anthracycline chemotherapy and durvalumab in TNBC [
52]. To our knowledge, the Neo-CheckRay trial is the first trial to examine the effect of the pre-operative addition of radiation therapy to the combination of immunotherapy with standard NACT in early luminal B BC.
Acknowledgements
Not applicable.
Sponsor identification
Sponsor: Institut Jules Bordet, Rue Héger Bordet 1, 1000 Brussels, Belgium.
Sponsor Protocol Number: IJB-LBC-NEOCHECKRAY-2018.
Trial identification
EudraCT Number: 2018–004165-13.
Role of study sponsor and funders
The sponsor (Institut Jules Bordet, Rue Héger Bordet 1, Brussels) detains ultimate authority on study design; collection, management, analysis, and interpretation of data; writing of the report; and the decision to submit the report for publication.
Composition, roles, and responsibilities of the coordinating centre, steering committee, endpoint adjudication committee, data management team
The coordinating centre is the clinical trials support unit (CTSU) of the Jules Bordet Institute. Information on the composition, roles and responsibilities of the CTSU can be found at
https://ctsu.bordet.be/#.
Protocol version and date on which this manuscript was based
Protocol version 2, dated 01/02/2020.
Names, affiliations, and roles of protocol contributors
Alex De Caluwé, Institut Jules Bordet, radiation oncologist, study chair.
Laurence Buisseret, Institut Jules Bordet, medical oncologist.
Philip Poortmans, GZA Antwerp, radiation oncologist.
Roberto Salgado, GZA Antwerp, pathologist.
Marianne Paesmans, Institut Jules Bordet, study statistician.
Fabien Reyal, Institut Curie, surgeon.
Martine Piccart, Institut Jules Bordet, medical oncologist.
Emanuela Romano, Institut Curie, medical oncologist, study co-chair.
Michail Ignatiadis, medical oncologist.
Study sites
Safety run-in: Institut Jules Bordet, Brussels, Belgium.
Phase II randomized trial: Institut Jules Bordet, Brussels, Belgium; Institut Curie, Paris, France; 4 other sites in Belgium and France to be confirmed.
Biological specimens
Biological specimens will be collected and stored for molecular analysis.
Protocol amendments
Important protocol modifications will be communicated to investigators, research ethics review process, regulators and trial registries.
Declarations
Competing interests
ADC: institutional research grant from AstraZeneca. LB: institutional research grant from AstraZeneca; speaker honoraria from BMS; travel grant from Roche. PP: part-time medical advisor for Sordina IORT Technologies s.p.a., since 1 April 2020, not related to this work. DVG: Advisory board/Honoraria received: Sanofi, Accuray, Merck-Pfizer, Takeda and Novartis. RS: non-financial support from Merck, non-financial support from BMS, other from Puma Biotechnology, other from Roche, other from Roche, other from Merck. DE: Research Funding (ESMO Fellowship): Novartis. Speaker fee: Janssen. MP: Board Member (Scientific Board): Oncolytics; Consultant (honoraria): AstraZeneca, Camel-IDS, Crescendo Biologics, Debiopharm, G1 Therapeutics, Genentech, Huya, Immunomedics, Lilly, Menarini, MSD, Novartis, Odonate, Periphagen, Pfizer, Roche, Seattle Genetics. Research grants to my Institute: AstraZeneca, Lilly, MSD, Novartis, Pfizer, Radius, Roche-Genetech, Servier, Synthon. No stock ownership. ER: no disclosures relevant to this project. MI: Consultant or advisory role (honoraria): Celgene, Novartis, Pfizer, Seattle Genetics, Tesaro. Research grants to my Institute: Roche, Menarini Silicon Biosystems, Janssen Diagnostics, Pfizer. No stock ownership. Travel grants: Pfizer, Amgen. All other authors: no competing interests disclosed.
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