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KOL Pulse · Clinical Trial Profile

ARC-20 Trial

ARC-20 is a Phase 1 study of casdatifan (AB521), an oral HIF-2α inhibitor from Arcus Biosciences, evaluated as monotherapy and in combinations in heavily pretreated advanced clear cell renal cell carcinoma. Results published in Nature showed durable clinical activity with a manageable safety profile. Casdatifan is investigational and not FDA approved.

Phase IAdvanced ccRCCArcus BiosciencesHIF-2α inhibitorNCT05536141Investigational
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At a Glance
ARC-20 — Key Takeaways

The 30-second summary

Design: Phase 1 (ARC-20), casdatifan (AB521) monotherapy and combinations in advanced clear cell RCC. Key readout: durable clinical activity in heavily pretreated patients, published in Nature. Regulatory: investigational — NOT FDA approved (belzutifan/Welireg is the approved HIF-2α inhibitor in RCC). Sponsor / drug: Arcus Biosciences; casdatifan (AB521, oral HIF-2α inhibitor).

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Who's Talking
KOL Leaders on ARC-20
Toni Choueiri, MD
Toni Choueiri, MD
@DrChoueiri
12,430 impressions
Yksel rn
Yksel rn
@DrYukselUrun
4,591 impressions
Chris Labaki
Chris Labaki
@Chrislabaki1
2,270 impressions
Jordan Ciuro, MD
Jordan Ciuro, MD
@jordanciuro
1,797 impressions
Rana McKay, MD, FASCO
Rana McKay, MD, FASCO
@DrRanaMcKay
1,629 impressions
Emre Yekedz
Emre Yekedz
@yekeduz_emre
1,481 impressions
The Data
Key Slides

Conference and publication slides shared by KOLs. Toggle the OCR text under each to read the extracted data verbatim.

@DrYukselUrun
@DrYukselUrun
Presented Slides
2025-02-15 · 4,591 impressions
View post ↗
ARC-20 slide - DrYukselUrunARC-20 slide - DrYukselUrunARC-20 slide - DrYukselUrunARC-20 slide - DrYukselUrun
@Chrislabaki1
@Chrislabaki1
Presented Slides
2025-02-15 · 2,270 impressions
View post ↗
ARC-20 slide - Chrislabaki1ARC-20 slide - Chrislabaki1
@jordanciuro
@jordanciuro
Presented Slides
2025-02-15 · 1,797 impressions
View post ↗
ARC-20 slide - jordanciuroARC-20 slide - jordanciuroARC-20 slide - jordanciuroARC-20 slide - jordanciuro
@DrRanaMcKay
@DrRanaMcKay
Presented Slides
2025-02-15 · 1,629 impressions
View post ↗
ARC-20 slide - DrRanaMcKayARC-20 slide - DrRanaMcKayARC-20 slide - DrRanaMcKayARC-20 slide - DrRanaMcKay
@yekeduz_emre
@yekeduz_emre
Presented Slides
2025-02-15 · 1,481 impressions
View post ↗
ARC-20 slide - yekeduz_emreARC-20 slide - yekeduz_emreARC-20 slide - yekeduz_emre
KOL Voices
Top Tweets by Reach
@DrChoueiri
@DrChoueiri
1/ Results from #ARC20 trial are out in @Nature! This trial evaluated the HIF-2α inhibitor Casdatifan in heavily pretreated advanced ccRCC and provides important insights into HIF-2α biology and response. This is the 2nd HIF2 inhibitor with enough activity to move to a pivotal https://t.co/jbFnSa4eq1
8,546 views120 likes2026-07-01
@JacobPlieth
@JacobPlieth
Is $RCUS casdatifan meaningfully different vs $MRK Welireg? My take on Arc-20 from #Enasymp24 via @ApexOnco -> https://t.co/kRXQUFWNd1
4,929 views8 likes2024-10-25
@DrYukselUrun
@DrYukselUrun
New kid on the block! @DrChoueiri HIF-2α Inhibitor Cas in ccRCC: Early Promise! -Active across IMDC risk groups in pretreated ccRCC. -Grade 3 anemia (36%) & hypoxia (6-9%), no Grade ≥4 TEAEs. -Next: PEAK-1 (Cas + Cabo) & first-line IO combo trials! #GU25 @asco @oncoalert… https://t.co/hfrVSbQvSY https://t.co/hoaXbd0gYn
4,591 views59 likes2025-02-15
@Chrislabaki1
@Chrislabaki1
@DrChoueiri with the results of the ARC-20 trial evaluating the safety and efficacy of castadifan monotherapy in previously treated #ccRCC with promising data #GU24 Next: Phase 3 PEAK-1 trial of Cabozantinib +/- Casdatifan in PD-1 treated #RCC @ASCO @DanaFarber https://t.co/N8QHu8C6yv
2,270 views28 likes2025-02-15
@jordanciuro
@jordanciuro
Updates of Casdatifan in previously treated ccRCC? Ph 1 ARC-20 safety and efficacy @ASCO #GU25 Key Takeaways; in N=93 Casdatifan: ✅At dose 100mg qday ORR in 33% ✅Well tolerated 🔎Pending updates from ph 3 #PEAK-1 trial evaluating 100 mg casdatifan with cabozantinib vs… https://t.co/7cZ1hZvJwc https://t.co/uuCviuCzHV
1,797 views17 likes2025-02-15
@DrRanaMcKay
@DrRanaMcKay
Exciting to see data from Arc20 of Casdatifan in ccRCC. ORR 33% at RP2D with primary PD<10%. Excited about the launch of Peak-1. @DrChoueiri @montypal #GU25 https://t.co/KDwQ3fT41U
1,629 views30 likes2025-02-15
@yekeduz_emre
@yekeduz_emre
⏩ @ASCO #GU25: @DrChoueiri is on the stage! Castadifan (HIF-2α inhibitor) shows promising activity & tolerability in heavily pretreated ccRCC, regardless of IMDC risk. ✅ Key Findings: 🔹 ORR observed, including PR & SD 🔹 Grade ≥3 TEAEs: 42% (BID), 36% (QD) 🔹 Most common… https://t.co/5T6oVOmhr5 https://t.co/9qqwLYJdAt
1,481 views15 likes2025-02-15
@SScagliarini_
@SScagliarini_
🗓️ 01 Jul 2026: A Great Day for ccRCC research and for patients! 🧬 💊 #Casdatifan & #Belzutifan ( + Pembro vs Pembro) @Nature & @NEJM 👏🏼 Congratulation to @DrChoueiri @DrRanaMcKay and @tompowles1 for their tremendous effort…from paving the way…to having another step forward https://t.co/YXulIUr9nE
1,081 views16 likes2026-07-01
@DrChoueiri
@DrChoueiri
2/ #ARC-20 is an open-label, multicenter clinical trial evaluating Casdatifan monotherapy in patients with advanced ccRCC who had previously received both PDL1-based and VEGFR-targeted therapy, a setting with limited treatment options and significant unmet need. @OncoAlert
896 views7 likes2026-07-01
@DrChoueiri
@DrChoueiri
8/ Consistently, tumors with higher HIF-2α staining (≥25%) demonstrated higher tEPO levels and were associated with significantly longer PFS (P = 0.006), further linking tumor HIF-2α activity with clinical benefit from Casdatifan https://t.co/eyljjEwdyC
791 views10 likes2026-07-01
Efficacy & Safety
Results

Overview

ARC-20 is a Phase 1 study of casdatifan (AB521), an oral hypoxia-inducible factor-2 alpha (HIF-2α) inhibitor from Arcus Biosciences, evaluated as monotherapy and in combination regimens in advanced clear cell renal cell carcinoma. Results published in Nature in 2026 showed durable clinical activity in heavily pretreated patients alongside biomarker correlates of HIF-2α engagement. Casdatifan is investigational and remains under active clinical development, including a Phase 3 program.

Primary endpoint — Efficacy (Phase 1)

In ARC-20, casdatifan demonstrated durable clinical activity in heavily pretreated advanced clear cell RCC, with results published in Nature. Response and duration figures, together with biomarker correlates of HIF-2α inhibition, were highlighted by KOLs in the posts above and detailed in the primary publication.

Durable activity in heavily pretreated ccRCC (Nature)

Safety

KOLs described a manageable safety profile consistent with HIF-2α inhibition, whose class-defining adverse events include anemia and hypoxia. See the KOL posts and the Nature publication for the detailed safety data.

Clinical implications

⚠️ Investigational — casdatifan (AB521) is NOT FDA approved. ARC-20 Phase 1 data support continued development as a next-generation HIF-2α inhibitor in clear cell RCC. Belzutifan (Welireg) is the currently FDA-approved HIF-2α inhibitor in this space (advanced and, as of June 2026, adjuvant RCC).

Community Reaction
KOL Sentiment
KOLComment (verbatim)Sentiment

@DrRanaMcKay		Exciting to see data from Arc20 of Casdatifan in ccRCC. ORR 33% at RP2D with primary PD<10%. Excited about the launch of Peak-1. @DrChoueiri @montypal #GU25 https://t.co/KDwQ3fT41UPositive

@DrChoueiri		1/ Results from #ARC20 trial are out in @Nature! This trial evaluated the HIF-2α inhibitor Casdatifan in heavily pretreated advanced ccRCC and provides important insights into HIF-2α biology and response. This is the 2nNeutral

@JacobPlieth		Is $RCUS casdatifan meaningfully different vs $MRK Welireg? My take on Arc-20 from #Enasymp24 via @ApexOnco -> https://t.co/kRXQUFWNd1Neutral

@DrYukselUrun		New kid on the block! @DrChoueiri HIF-2α Inhibitor Cas in ccRCC: Early Promise! -Active across IMDC risk groups in pretreated ccRCC. -Grade 3 anemia (36%) & hypoxia (6-9%), no Grade ≥4 TEAEs. -Next: PEAK-1 (Cas + CaNeutral

@Chrislabaki1		@DrChoueiri with the results of the ARC-20 trial evaluating the safety and efficacy of castadifan monotherapy in previously treated #ccRCC with promising data #GU24 Next: Phase 3 PEAK-1 trial of Cabozantinib +/- CasdatiNeutral

@jordanciuro		Updates of Casdatifan in previously treated ccRCC? Ph 1 ARC-20 safety and efficacy @ASCO #GU25 Key Takeaways; in N=93 Casdatifan: ✅At dose 100mg qday ORR in 33% ✅Well tolerated 🔎Pending updates from ph 3 #PEAK-1 trial Neutral

@yekeduz_emre		⏩ @ASCO #GU25: @DrChoueiri is on the stage! Castadifan (HIF-2α inhibitor) shows promising activity & tolerability in heavily pretreated ccRCC, regardless of IMDC risk. ✅ Key Findings: 🔹 ORR observed, including PRNeutral

@SScagliarini_		🗓️ 01 Jul 2026: A Great Day for ccRCC research and for patients! 🧬 💊 #Casdatifan & #Belzutifan ( + Pembro vs Pembro) @Nature & @NEJM 👏🏼 Congratulation to @DrChoueiri @DrRanaMcKay and @tompowles1 for their tremeNeutral

@DrChoueiri		2/ #ARC-20 is an open-label, multicenter clinical trial evaluating Casdatifan monotherapy in patients with advanced ccRCC who had previously received both PDL1-based and VEGFR-targeted therapy, a setting with limited treNeutral

@DrChoueiri		8/ Consistently, tumors with higher HIF-2α staining (≥25%) demonstrated higher tEPO levels and were associated with significantly longer PFS (P = 0.006), further linking tumor HIF-2α activity with clinical benefit from CNeutral

@DrChoueiri		2/ After FDA approval of belzutifan & exciting results from LITESPARK-005/003, casdatifan emerges as a novel HIF-2α inhibitor in ccRCC: ARC-20 shows early activity & manageable safety. PEAK-1 PhIII to combine CaNeutral

@DrChoueiri		10/ In summary, Casdatifan demonstrated durable clinical activity in heavily pretreated advanced ccRCC while providing important insights into HIF-2α biology. The association of EPO suppression and hypoxia-related transcNeutral

@DrChoueiri		6/ Biomarker correlates findings: A hallmark pharmacodynamic effect of Casdatifan was this profound suppression of EPO with 68% of patients achieving > 80% maximal reduction in EPO. Now, it gets interestingEPO suppreNeutral

@niklas_kluemper		🚨 Results from #ARC20 are out in @Nature! This study evaluated the HIF-2α inhibitor casdatifan in heavily pretreated advanced ccRCC, providing important insights into HIF-2α biology and response. Casdatifan is now the sNeutral

@BertrandBio		$RCUS ARC-20 cas' (HIF-2a inh) update from #GU25 #ASCOGU25 (cont'd) WF / Swimmer / PFS KM plot @ cas 50mg BID & QD https://t.co/tbbJWoRKW0Neutral

@BertrandBio		$RCUS ARC-20 cas' (HIF-2a inh) update from #GU25 #ASCOGU25 (cont'd) cas safety comp & efficacy bench vs $MRK Welireg (x-trial) https://t.co/Tm9Ivoq2OgNeutral

@weoncologists		Just Out 🏹 ARC-20 study in nature🚨 Casdatifan, a selective HIF-2α inhibitor, demonstrated meaningful and durable antitumour activity with manageable safety in refractory metastatic clear cell renal cell carcinoma #kidneNeutral

@katy_beckermann		@DrChoueiri @Nature @DanaFarber @DanaFarberNews @harvardmed @DrRanaMcKay @montypal @neerajaiims @VivekSubbiah @ASCO @myESMO @ASCOPres Congratulations @DrChoueiri and team on this high-impact paper in @Nature! 🎉 Exciting Neutral
Answers
Frequently Asked Questions
What is the ARC-20 trial?
ARC-20 is a Phase 1 study of casdatifan (AB521), an oral HIF-2α inhibitor from Arcus Biosciences, evaluated as monotherapy and in combinations in advanced clear cell renal cell carcinoma (NCT05536141).
Is casdatifan FDA approved?
No. Casdatifan (AB521) is investigational and not FDA approved. Belzutifan (Welireg) is the currently approved HIF-2α inhibitor in renal cell carcinoma.
What did ARC-20 show?
ARC-20 showed durable clinical activity for casdatifan in heavily pretreated advanced clear cell RCC, with results published in Nature and accompanied by biomarker correlates of HIF-2α inhibition.
Who sponsors ARC-20?
ARC-20 is sponsored by Arcus Biosciences.
How does casdatifan work?
Casdatifan is an oral inhibitor of HIF-2α (hypoxia-inducible factor 2 alpha), a transcription factor central to clear cell RCC biology — the same target class as belzutifan.