Unleashing NK- and CD8 T cells by combining monalizumab and trastuzumab for metastatic HER2-positive breast cancer: Results of the MIMOSA trial

The large majority of patients with HER2-positive metastatic breast cancer (MBC) will eventually develop resistance to anti-HER2 therapy and die of this disease. Despite, relatively high levels of stromal tumor infiltrating lymphocytes (sTILs), PD1-blockade has only shown modest responses. Monalizumab targets the inhibitory immune checkpoint NKG2A, thereby unleashing NK- and CD8 T cells. We hypothesized that monalizumab synergizes with trastuzumab by promoting antibody-dependent cell-mediated cytotoxicity. In the phase II MIMOSA-trial, HER2-positive MBC patients were treated with trastuzumab and 750 mg monalizumab every two weeks. Following a Simon's two-stage design, 11 patients were included in stage I of the trial. Treatment was well tolerated with no dose-limiting toxicities. No objective responses were observed. Therefore, the MIMOSA-trial did not meet its primary endpoint. In summary, despite the strong preclinical rationale, the novel combination of monalizumab and trastuzumab does not induce objective responses in heavily pre-treated HER2-positive MBC patients.

Current and future diagnostic and treatment strategies for patients with invasive lobular breast cancer

BACKGROUND

Invasive lobular breast cancer (ILC) is the second most common type of breast cancer after invasive breast cancer of no special type (NST), representing up to 15% of all breast cancers.

DESIGN

Latest data on ILC are presented, focusing on diagnosis, molecular make-up according to the European Society for Medical Oncology Scale for Clinical Actionability of molecular Targets (ESCAT) guidelines, treatment in the early and metastatic setting and ILC-focused clinical trials.

RESULTS

At the imaging level, magnetic resonance imaging-based and novel positron emission tomography/computed tomography-based techniques can overcome the limitations of currently used imaging techniques for diagnosing ILC. At the pathology level, E-cadherin immunohistochemistry could help improving inter-pathologist agreement. The majority of patients with ILC do not seem to benefit as much from (neo-)adjuvant chemotherapy as patients with NST, although chemotherapy might be required in a subset of high-risk patients. No differences in treatment efficacy are seen for anti-human epidermal growth factor receptor 2 (HER2) therapies in the adjuvant setting and cyclin-dependent kinases 4 and 6 inhibitors in the metastatic setting. The clinical utility of the commercially available prognostic gene expression-based tests is unclear for patients with ILC. Several ESCAT alterations differ in frequency between ILC and NST. Germline BRCA1 and PALB2 alterations are less frequent in patients with ILC, while germline CDH1 (gene coding for E-cadherin) alterations are more frequent in patients with ILC. Somatic HER2 mutations are more frequent in ILC, especially in metastases (15% ILC versus 5% NST). A high tumour mutational burden, relevant for immune checkpoint inhibition, is more frequent in ILC metastases (16%) than in NST metastases (5%). Tumours with somatic inactivating CDH1 mutations may be vulnerable for treatment with ROS1 inhibitors, a concept currently investigated in early and metastatic ILC.

CONCLUSION

ILC is a unique malignancy based on its pathological and biological features leading to differences in diagnosis as well as in treatment response, resistance and targets as compared to NST.

High tumor mutation burden fails to predict immune checkpoint blockade response across all cancer types

BACKGROUND

High tumor mutation burden (TMB-H) has been proposed as a predictive biomarker for response to immune checkpoint blockade (ICB), largely due to the potential for tumor mutations to generate immunogenic neoantigens. Despite recent pan-cancer approval of ICB treatment for any TMB-H tumor, as assessed by the targeted FoundationOne CDx assay in nine tumor types, the utility of this biomarker has not been fully demonstrated across all cancers.

PATIENTS AND METHODS

Data from over 10 000 patient tumors included in The Cancer Genome Atlas were used to compare approaches to determine TMB and identify the correlation between predicted neoantigen load and CD8 T cells. Association of TMB with ICB treatment outcomes was analyzed by both objective response rates (ORRs, N = 1551) and overall survival (OS, N = 1936).

RESULTS

In cancer types where CD8 T-cell levels positively correlated with neoantigen load, such as melanoma, lung, and bladder cancers, TMB-H tumors exhibited a 39.8% ORR to ICB [95% confidence interval (CI) 34.9-44.8], which was significantly higher than that observed in low TMB (TMB-L) tumors [odds ratio (OR) = 4.1, 95% CI 2.9-5.8, P < 2 × 10^-16]. In cancer types that showed no relationship between CD8 T-cell levels and neoantigen load, such as breast cancer, prostate cancer, and glioma, TMB-H tumors failed to achieve a 20% ORR (ORR = 15.3%, 95% CI 9.2-23.4, P = 0.95), and exhibited a significantly lower ORR relative to TMB-L tumors (OR = 0.46, 95% CI 0.24-0.88, P = 0.02). Bulk ORRs were not significantly different between the two categories of tumors (P = 0.10) for patient cohorts assessed. Equivalent results were obtained by analyzing OS and by treating TMB as a continuous variable.

CONCLUSIONS

Our analysis failed to support application of TMB-H as a biomarker for treatment with ICB in all solid cancer types. Further tumor type-specific studies are warranted.

Abstract SP084: Replication stress response defects predict responses to ICT in non-hypermutated tumors

Immune checkpoint blockade (ICT) has provided robust, durable responses to a subset of patients. Many initial ICT trials were focused on highly mutated cancer types, such as melanoma and lung cancer, largely predicated on the idea that mutation-derived neoantigens would allow for generation of tumor-specific T cells. Subsequent analysis of patient responses in these highly mutated cancer types confirmed that increased tumor mutation burden (TMB) corresponded with improved patient outcomes. Further clinical studies identified additional predictive biomarkers, such as PD-L1 protein expression, and various gene expression signatures. Based on the success of ICT in hypermutated cancer types, further clinical trials with ICT were performed in cancers with overall lower mutational burden. These studies have indicated that many non-hypermutated cancer types with relatively low TMB may be effectively treated with ICT. For example, patients with clear cell renal cell carcinoma (ccRCC) display relatively low TMB overall, and a narrow distribution of TMB across patients, yet clinical response rates to ICT are ~30%, with some durable responses seen. Other tumor types with minimal mutation burdens, including glioblastoma (GBM) and triple negative breast cancer (TNBC), have likewise shown encouraging clinical responses to ICT. We recently demonstrated distinct tumor immunobiology between hypermutated and non-hypermutated tumor types, notably that relative neoantigen load/tumor mutation burden was only a relevant factor for immune infiltration in hypermutated tumor types. Consistent with this, clinical trials have demonstrated that TMB does not predict response to ICT in tumor types with minimal mutational load, such as breast cancer, ccRCC, and GBM. Thus, there remains a critical gap in knowledge as to how to identify which patients with non-hypermutated cancer may benefit from ICT. Here, we demonstrate that a replication stress response (RSR) defect gene expression signature accurately predicts ICT response in 11 independent non-hypermutated patient cohorts from 6 tumor types for which other biomarkers failed. Pre-clinical studies indicate that aberrant origin firing in RSR deficient tumor cells causes exhaustion of replication protein A, resulting in accumulation of immunostimulatory cytosolic DNA. Induction or suppression of RSR deficiencies was sufficient to modulate response to ICT. Taken together, the RSR defect gene signature can accurately identify patients who will benefit from ICT across numerous non-hypermutated tumor types, and pharmacological induction of RSR defects may further expand the benefits of ICT to more patients.

Citation Format: D McGrail, P Pilié, XHF Zhang, J Rosen, L Voorwerk, M Kok, A Heimberger, C Peterson, E Jonasch, S Lin. Replication stress response defects predict responses to ICT in non-hypermutated tumors [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr SP084.