First Clinical Data for Arcus Biosciences' HIF-2a Inhibitor, Casdatifan, Showed Promising Clinical Activity and Tumor Shrinkage in Patients with Metastatic Kidney Cancer

• Objective response rate of 34% (2 responses pending confirmation) and 25% (confirmed) in the 100mg daily dose expansion cohort (n=32) of ARC-20, a Phase 1/1b study of casdatifan in metastatic clear cell renal cell carcinoma (ccRCC)

• Low rate of primary progression (19%) and high rate of disease control (81%) was observed in the 100mg expansion cohort with many of those patients still on treatment

• Arcus will host a conference call to discuss these results, including results from the 50mg expansion cohort, at 5:00 AM PT / 8:00 AM ET today

Arcus Biosciences, Inc. (NYSE:RCUS), a clinical-stage, global biopharmaceutical company focused on developing differentiated molecules and combination therapies for patients with cancer, today presented the first clinical activity data for casdatifan, a HIF-2a inhibitor with best-in-class potential, in an oral plenary session by Dr. Toni K. Choueiri, Dana-Farber Cancer Institute at the 2024 EORTC-NCI-AACR Symposium on Molecular Targets and Cancer Therapeutics in Barcelona, Spain.

"Based on our experience in the ARC-20 study, we have seen casdatifan's ability to quickly bring tumor growth under control and its high response and disease control rates," said Toni K. Choueiri, M.D., director of the Lank Center for Genitourinary (GU) Oncology at Dana-Farber, the Jerome and Nancy Kohlberg chair and professor of medicine at Harvard Medical School and lead investigator of ARC-20. "Based on these data, casdatifan has the potential to be a future treatment option for kidney cancer. I am particularly interested in planned research into novel combinations for casdatifan in both first- and second-line ccRCC."

"In the 100mg daily dose-expansion cohort of ARC-20, casdatifan showed encouraging results, particularly a low primary progressive disease rate and very durable responses. This was accomplished with a manageable safety profile," said Dimitry Nuyten, M.D., Ph.D., chief medical officer of Arcus. "These data support the potential for casdatifan to be a best-in-class HIF-2a inhibitor for the treatment of ccRCC. We look forward to initiating our first Phase 3 study for casdatifan, PEAK-1, in the first half of 2025, and expanding our development program into the first-line setting with a novel combination, as well as into other ccRCC subpopulations."

ARC-20 is a Phase 1/1b dose-escalation and -expansion study. In the dose escalation (20mg to 200mg) portion of the study, the safety profile was comparable across the doses; there were no dose-limiting toxicities, and the maximum tolerated dose was not reached at daily doses of up to 150 mg (200 mg portion of the study is currently ongoing). The 100 mg daily dose (50 mg BID [twice daily]) was selected for dose expansion, and casdatifan was evaluated in patients with metastatic ccRCC who had progressed on at least two prior lines of therapy, including both an anti-PD-1 and a tyrosine kinase inhibitor (TKI) therapy (n=33). The patient population was heavily pre-treated: 52% had received at least three prior lines of therapy; 26% had received at least four prior lines of therapy; and 61% had an International Metastatic Renal Cell Carcinoma Database Consortium (IMDC) risk factor of intermediate.

At the time of data cut off (DCO, Aug. 30, 2024), median follow-up was 11 months. Casdatifan showed a rapid time to response, and only 19% of patients had primary progressive disease (progressed at or before their first disease assessment). The majority of patients (81%) experienced disease control with either a partial response or stable disease. At the time of the DCO, the median progression-free survival had not been reached. 34% of patients experienced an objective response, meaning their tumor shrank by at least 30%. A summary of initial results is below.

In the 100mg dose-expansion cohort, no unexpected safety signals were observed at the time of DCO, and casdatifan had an acceptable and manageable safety profile. Grade 3 treatment-emergent adverse events (TEAEs) related to casdatifan were 42%, including anemia (36%) and hypoxia (9%). No patients discontinued treatment from anemia. No TEAEs were life-threatening or led to death.

Arcus is pursuing a broad development program in both the first-line and post-anti-PD-1 settings with differentiated combinations to maximize the opportunity for casdatifan in ccRCC. In addition to the monotherapy cohorts of ARC-20, the study is also enrolling a cohort to evaluate casdatifan in combination with cabozantinib, a VEGFR TKI which is intended to support the initiation of Arcus's planned first Phase 3 study, PEAK-1, evaluating casdatifan in combination with cabozantinib versus cabozantinib monotherapy in patients with metastatic ccRCC who have previously received anti-PD-1 therapy. The primary endpoint will be progression-free survival with a key secondary endpoint of overall survival. Arcus also recently announced a clinical collaboration as part of its first-line strategy in advanced ccRCC to evaluate casdatifan in combination with volrustomig, an investigational anti-PD-1/CTLA-4 bispecific antibody.

Investors may dial in to the conference call at +1 (404) 975- 4839 (local) or +1 (833) 470-1428 (toll-free), using Conference ID: 595409 on Thursday, October 24, 2024 at 5:00 AM PT / 8:00 AM ET. Participants may also register for the call online using the following link: https://www.netroadshow.com/events/login?show=a0338351&confId=70796. In addition to the ARC-20 data, the conference call will address the development strategy and market potential for casdatifan. Arcus will also be joined by Dr. Rana McKay of the University of California San Diego. To access the live webcast and accompanying slide presentation, please visit the "Investors & Media" section of the Arcus Biosciences website at www.arcusbio.com. A replay will be available following the live event.

About Casdatifan (AB521)

Casdatifan is a small-molecule inhibitor of HIF-2a, a tumorigenic transcription factor involved in oxygen sensing in multiple organs as well as in tumors. Clear cell RCC is almost universally associated with HIF-2a dysregulation as a result of genetic abnormalities in the VHL pathway. This creates a situation of pseudohypoxia and the abnormal increase in HIF-2a-mediated expression of a broad range of oncogenic proteins. By selectively inhibiting HIF-2a, casdatifan is designed to disable a wide array of pathways involved in tumor proliferation and survival, treatment resistance and angiogenesis, leading to cancer cell death. Casdatifan is being evaluated in ARC-20, a Phase 1/1b study in cancer patients, and STELLAR-009, a Phase 1b/2 study in combination with zanzalintinib in patients with advanced solid tumors, including ccRCC.

Under the Gilead and Arcus collaboration agreement, Gilead has the right to opt-in to development and commercialization for casdatifan after Arcus's delivery of a qualifying data package.

Casdatifan is an investigational molecule. Approval from any regulatory authority for its use has not been received, and its safety and efficacy have not been established.

About RCC

According to the American Cancer Society, kidney cancer is among the top 10 most commonly diagnosed forms of cancer among both men and women in the U.S., and an estimated 81,600 Americans will be diagnosed with kidney cancer in 2024. Clear cell RCC is the most common type of kidney cancer in adults. If detected in its early stages, the five-year survival rate for RCC is high; for patients with advanced or late-stage metastatic RCC, however, the five-year survival rate is only 15%. In 2022, approximately 32,200 patients with advanced kidney cancer required systemic therapy in the U.S., with over 20,000 patients receiving first-line treatment.

About Arcus Biosciences

Arcus Biosciences is a clinical-stage, global biopharmaceutical company developing differentiated molecules and combination medicines for people with cancer. In partnership with industry collaborators, patients and physicians around the world, Arcus is expediting the development of first- or best-in-class medicines against well-characterized biological targets and pathways and studying novel, biology-driven combinations that have the potential to help people with cancer live longer. Founded in 2015, the company has expedited the development of multiple investigational medicines into clinical studies, including new combination approaches that target TIGIT, PD-1, HIF-2a, CD73, dual A2a/A2b receptor, CD39, and AXL. For more information about Arcus Biosciences' clinical and preclinical programs, please visit www.arcusbio.com.

Forward Looking Statements

This press release contains forward-looking statements. All statements regarding events or results to occur in the future contained herein are forward-looking statements reflecting the current beliefs and expectations of management made pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995, including, but not limited to, the statements in Dr. Nuyten's and Dr. Choueiri's quotes and statements regarding: the potency, efficacy or safety of casdatifan, including its potential for a best-in-class profile; casdatifan's safety profile; ability for casdatifan to be used in first-line therapy; how data from ARC-20 will support or advance Arcus's development program for casdatifan, including plans for future development; plans to initiate a new Phase 3 study with casdatifan, including timing for initiating any such study; and combinations that Arcus plans to explore in future studies. All forward-looking statements involve known and unknown risks and uncertainties and other important factors that may cause Arcus's actual results, performance or achievements to differ significantly from those expressed or implied by the forward-looking statements. Factors that could cause or contribute to such differences include, but are not limited to risks associated with: interim data not being replicated in future studies evaluating the same investigational molecules or regimen; the unexpected emergence of adverse events or other undesirable side effects in Arcus's investigational products; risks associated with manufacturing or supplying product for such clinical trials; uncertainties in timelines associated with the conduct of clinical studies and with respect to the regulatory application process; difficulties associated with the management of the collaboration activities with our strategic partners or expanded clinical programs; changes in the competitive landscape for Arcus's programs; and the inherent uncertainty associated with pharmaceutical product development and clinical trials. Risks and uncertainties facing Arcus are described more fully in the "Risk Factors" section of Arcus's most recent periodic report filed with the U.S. Securities and Exchange Commission. You are cautioned not to place undue reliance on the forward-looking statements, which speak only as of the date of this press release. Arcus disclaims any obligation or undertaking to update, supplement or revise any forward-looking statements contained in this press release except to the extent required by law.

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