FDA Grants Accelerated Approval to Tarlatamab (Imdelltra) for Earlier-Stage Small Cell Lung Cancer
The bispecific antibody targeting DLL3 and CD3, previously approved for later lines of therapy, is now authorized for use after progression on first-line platinum-based chemotherapy, based on data from the phase 3 DeLLphi-304 trial showing a significant improvement in overall survival.
We are witnessing a rare moment in oncology—when a drug from the most hopeless niche breaks out not through flashy response rates, but through mathematically unassailable survival statistics. 13.6 months versus 8.3—this is not a clinical nuance; it is a death sentence for the old standard. But the real story isn't just the numbers. It's the trajectory: tarlatamab starts separating Kaplan-Meier curves not after six months, as is typical with immunotherapy, but from the first month. The second factor that should make investors rethink their models: the 40% reduction in risk of death is reproducible across the most stubborn subgroups—patients with platinum resistance, brain metastases, and those who failed anti-PD-(L)1 therapy. No drug in the history of small cell lung cancer has demonstrated such universality. This means Amgen has not just secured a linear label expansion; it has rewritten the standard of care for second-line treatment of a disease that has seen nothing but toxic topotecan with its meager 7.5 months of life for thirty years.
Timeline and Context: Thirty Years of Waiting and One Molecule
The story of DLL3 as a target is a graveyard of ambitions. Back in 2016, AbbVie (yes, the same AbbVie now nipping at Amgen's heels) launched the antibody-drug conjugate rovalpituzumab tesirine (Rova-T) targeting DLL3. The results were catastrophic: extreme toxicity, zero efficacy, and the program was shut down with a $5.8 billion loss. At the time, DLL3 seemed like a dead target. But Amgen saw it differently: the problem wasn't DLL3, but the payload. Conjugates fail because small cell lung cancer mutates rapidly and loses sensitivity to cytotoxins. The solution isn't to poison the cell, but to bring a T-cell to it.
- FDA grants accelerated approval to tarlatamab based on phase 2 DeLLphi-301 data: a 40% response rate and median duration of response of 9.7 months in patients who had received two or more prior lines of therapy. The market reacts cautiously—after all, the data is non-randomized and the population is small.
September-November 2025. At ESMO and subsequently in the New England Journal of Medicine, results from the phase 3 DeLLphi-304 trial are published—a multicenter, randomized study involving 509 patients. Median overall survival: 13.6 vs. 8.3 months, p<0.001. Objective response rate: 35% vs. 20%. Serious adverse events: 54% vs. 80% with chemotherapy. The drug also improves cough and dyspnea better than chemotherapy.
May 2026. With full phase 3 data in hand, the FDA removes the accelerated approval status and grants full approval for tarlatamab in the second-line setting. Simultaneously, the CHMP in Europe recommends approval, opening up EU markets.
Winners and Losers: A New Balance of Power
Amgen wins, but not just from sales (peak sales of Imdelltra are forecast at $2.8-3.2 billion by 2029). The key asset Amgen gains is the BiTE (Bispecific T-cell Engager) platform. Tarlatamab validates the concept itself: if a BiTE works in small cell lung cancer—one of the most aggressive and rapidly mutating tumors—it will work in other neuroendocrine tumors. Expect Amgen to launch trials of tarlatamab in neuroendocrine prostate cancer by the end of 2026.
The loser is not so much chemotherapy as the DLL3 competitors who didn't make it in time. Merck with MK-6070 (a trispecific T-cell engager acquired for $650 million from Harpoon) is 2-3 years behind. Daiichi Sankyo, which paid $170 million for a stake in the same asset, is also playing catch-up. But the biggest loser is AbbVie. They were first with Rova-T and lost. Now they're back, paying a $100 million upfront and promising up to $1.075 billion for the trispecific ZG006 (alveltamig) from China's Zelgen. The problem is that by the time ZG006 hits the market (2028-2029), tarlatamab will have already consumed the entire second-line space, and potentially the first-line as well (Amgen is already testing tarlatamab in combination with durvalumab as maintenance therapy after platinum).
What the Media Misses: The Trojan Horse of First-Line Therapy
The key non-obvious fact that news outlets overlooked: DeLLphi-304 is not an endpoint, but a springboard. Amgen has already launched the phase 3 DeLLphi-306 trial, in which tarlatamab is added to standard chemotherapy and durvalumab in the first-line setting. This is a superiority-design trial, and if positive, tarlatamab will become not just a salvage therapy, but the treatment of choice for all patients with small cell lung cancer from the moment of diagnosis.
Why is this critical? Because the first-line patient population is 3-4 times larger than second- and third-line combined. This transforms a drug with a $700 million market (relapsed niche) into a blockbuster with a potential $6 billion market. That's why Amgen is aggressively pushing for second-line approval—it creates a safety precedent and gives physicians experience with BiTE before the drug moves to first-line. In effect, Amgen is using the second-line as a training ground for oncologists and a proof-of-concept for regulators.
The second point glossed over in press releases: the issue of cytokine release syndrome (CRS). Yes, the rate of grade ≥3 CRS in DeLLphi-304 is low (around 2-3%), but that's because Amgen implemented hospitalization for the first two cycles and premedication with dexamethasone. This creates a hidden logistical burden on the healthcare system: tarlatamab cannot simply be prescribed at a pharmacy; the patient must spend 48 hours in the hospital. In the US, this adds $12,000-15,000 to the cost of the course, which is not included in the drug's price. Clinics with infrastructure for CRS monitoring benefit; small oncology practices that cannot afford it lose out.
Forecast: The Next 30 and 90 Days
In the next 30 days, expect two events. First: Amgen will announce the price for the European market. Given that the annual course in the US costs around $256,000, the European price will be in the range of €120,000-145,000 after negotiations with NICE and IQWiG. Second: AbbVie will release updated data on its trispecific antibody ZG006, trying to show an advantage over tarlatamab in depth of response. Watch the population closely: if Zelgen/AbbVie present data only from an Asian cohort, it's a weak signal that efficacy may not replicate in European populations.
Within 90 days, a tectonic shift will occur: Amgen will file for accelerated approval of tarlatamab in the first-line setting using interim data from DeLLphi-306. The FDA, armed with retrospective analysis results—a 35% reduction in risk of death across any subgroup in DeLLphi-304, including patients with a platinum-free interval of zero—may take an unprecedented step: approving a BiTE in the first-line without full phase 3 data. This would set a precedent that could send shares of Merck, Daiichi Sankyo, and AbbVie in the DLL3 segment down 8-15% in a single trading day. And then we will be discussing not the success of a single molecule, but the birth of a new paradigm: immunotherapy has ceased to be a "support" for chemotherapy and has become its replacement. Small cell lung cancer is no longer a death sentence with a median of 8 months, but a manageable chronic disease. 13.6 months is just the beginning of the curve.
— Editorial Team
