Key Ideas
Tarlatamab, a bispecific T-cell engager that targets DLL3, received FDA approval in May 2024 for relapsed small cell lung cancer, offering meaningful, durable responses where chemotherapy options had been limited. It works by directing a patient's own T cells to attack DLL3-expressing tumor cells, and its main risks are cytokine release syndrome and delayed-onset neurotoxicity.
A New Option for a Historically Difficult Cancer
Small cell lung cancer has long been considered one of the more difficult diagnoses in thoracic oncology. For years, treatment options plateaued at a handful of chemotherapy regimens with modest, short-lived benefit. That picture is finally starting to change. A new class of bispecific T-cell engagers targeting a protein called DLL3 is providing meaningful, durable responses for patients who previously had very few options left to try.
What Makes Small Cell Lung Cancer Hard to Detect and Treat
The name itself dates back to the 1980s, when pathologists distinguishing lung cancer subtypes under the microscope categorized tumors as either small cell or non-small cell based on cell appearance. Small cell lung cancer now accounts for roughly 10 to 15 percent of all lung cancer diagnoses, a proportion that has declined over time.
Lung cancer screening programs have improved early detection of many lung cancers, but small cell tumors tend to grow quickly between the intervals of annual screening scans, so they are often missed. As a result, more than three-quarters of patients present with extensive-stage disease at diagnosis, limiting treatment options from the outset.
How Checkpoint Inhibitor Immunotherapy Changed Small Cell Lung Cancer Survival
The introduction of immunotherapy, specifically PD-L1 checkpoint inhibitors, marked the first real shift in outcomes for extensive-stage small cell lung cancer in decades. Randomized trials combining checkpoint inhibitors with platinum-based chemotherapy produced something clinicians had not seen before in this disease: a tail on the survival curve, meaning a subset of patients living for an extended period rather than the survival curves collapsing toward zero as they had with chemotherapy alone.
That said, the benefit has not been universal. Not every patient responds to immunotherapy, and once patients progress, the available chemotherapy options offer only single-digit response rates. A new approach was clearly needed.
What Is DLL3 and Why It Matters in Small Cell Lung Cancer
Delta-like ligand 3, or DLL3, emerged as a promising target because of its expression pattern. Normal cells express very little DLL3 on their surface, but neuroendocrine small cell tumors express it at high levels, a contrast that makes DLL3 an attractive, relatively tumor-specific target for immune-based therapy.
Tarlatamab: FDA-Approved DLL3-Targeted Therapy for Relapsed Small Cell Lung Cancer
Tarlatamab is a bispecific T-cell engager designed to bind DLL3 on the tumor cell and CD3 on T cells, directing the immune system toward DLL3-expressing small cell lung cancer cells. Early-phase studies using this mechanism showed encouraging activity, which was ultimately confirmed in a pivotal randomized trial in patients with recurrent small cell lung cancer who had already progressed on platinum-based chemotherapy. Eligible patients needed a reasonable performance status and an expected life expectancy sufficient to complete treatment, criteria that can be difficult to meet in a population where tumors often progress rapidly.
Tarlatamab Efficacy in Relapsed Small Cell Lung Cancer
The response rates reported in that trial represented a substantial change from what has historically been possible in relapsed small cell lung cancer, leading to FDA approval in May 2024.
Tarlatamab Side Effects: Cytokine Release Syndrome and Neurotoxicity Risk
The toxicity profile reflects what is now a familiar pattern for T-cell engaging therapies: cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS), the latter of which frequently has a delayed onset, often around one month after starting therapy. Grade 3 toxicity rates were reported at roughly 27 percent with tarlatamab, a number that looks more favorable when compared against the toxicity burden of standard chemotherapy in this setting, which exceeds 60 percent. The most common grade 3 toxicities with tarlatamab were neutropenia and lymphopenia, compared with anemia and neutropenia with chemotherapy. Overall, the regimen is well tolerated in a patient population that frequently presents in poor condition at the time of relapse.
Access Barriers to Tarlatamab and Outpatient CRS Monitoring
Toxicity management drives much of the complexity around delivering this therapy. Access to agents like tocilizumab for CRS management is not universally available outside of centers set up for intensive monitoring, and the FDA label requires patients to live within about one hour of the infusion site. That requirement, combined with a step-up dosing schedule requiring inpatient monitoring for the first two doses and an initial six- to eight-hour observation period for outpatient doses thereafter, means treatment currently remains concentrated at academic centers rather than community practices. For patients traveling long distances, that can mean losing a full day, both for themselves and for caregivers, with every treatment cycle.
Future Directions for DLL3-Targeted Therapy in Lung Cancer
Ongoing trials are working to expand the role of DLL3-targeted therapy earlier in the treatment course. One study is evaluating a maintenance strategy that would move the drug out of the second-line setting, while another is testing its use in the first-line setting in combination with existing standards of care. Other companies are developing additional DLL3-directed bispecific and trispecific agents, suggesting this target will remain an active area of investigation for some time.
For Patients
If a diagnosis of small cell lung cancer has been given, know that treatment options have expanded meaningfully in the past few years. Immunotherapy combined with chemotherapy is now standard for many patients at diagnosis, and for those whose disease returns, a newer type of treatment that engages the body's own immune cells against the tumor is now FDA approved and available at select cancer centers. Because this treatment currently requires closer monitoring and travel to specialized centers, it is worth discussing with the care team whether referral to an academic cancer center may open up additional options.
Key Takeaways
-
Small cell lung cancer makes up 10 to 15 percent of lung cancers and is often diagnosed at an advanced stage because it grows rapidly between screening intervals.
-
Checkpoint inhibitor immunotherapy added to chemotherapy has produced the first durable long-term survivors in extensive-stage disease.
-
DLL3 is highly expressed on small cell tumor cells and minimally expressed on normal tissue, making it an attractive treatment target.
-
Tarlatamab, a DLL3-directed bispecific T-cell engager, received FDA approval in May 2024 for relapsed small cell lung cancer based on strong response data.
-
Cytokine release syndrome and delayed-onset neurotoxicity are the main safety considerations, though overall toxicity compares favorably with standard chemotherapy.
-
Current delivery requirements, including proximity to the treating center and step-up dosing observation, currently limit access mainly to academic centers.
-
Ongoing trials are testing whether DLL3-targeted therapy can move earlier into the treatment course, including maintenance and first-line settings.
References
-
Horn L, Mansfield AS, Szczesna A, et al. First-line atezolizumab plus chemotherapy in extensive-stage small-cell lung cancer. N Engl J Med. 2018.
-
Paz-Ares L, Dvorkin M, Chen Y, et al. Durvalumab plus platinum-etoposide versus platinum-etoposide in first-line treatment of extensive-stage small-cell lung cancer (CASPIAN): a randomised, controlled, open-label, phase 3 trial. Lancet. 2019.
-
Ahn MJ, Cho BC, Felip E, et al. Tarlatamab for patients with previously treated small-cell lung cancer. N Engl J Med. 2023.
-
U.S. Food and Drug Administration. FDA grants accelerated approval to tarlatamab-dlle for extensive stage small cell lung cancer. May 2024.