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A Phase 1/2 Clinical Trial to Assess the Safety, Tolerability, Pharmacokinetics and Preliminary Efficacy of HMBD-501 in Patients With HER3-Expressing Solid Tumors
What is small cell lung cancer?
Lung cancers split into two families by how the cells look under a microscope. Non small cell lung cancer is about 85 percent of cases and is covered on our lung cancer clinical trials page. Small cell lung cancer is the other 15 percent: a neuroendocrine cancer made of small, fast dividing cells that usually starts in the airways near the center of the chest. It is almost always caused by smoking, it tends to spread to lymph nodes, the brain, liver, and bones before it causes symptoms, and about two thirds of people are diagnosed after it has already spread. Doctors use a two stage system. Limited stage means the cancer is confined to one side of the chest and can be covered by a single radiation field, about 30 percent of cases. Extensive stage means it has spread beyond that.
The disease responds dramatically to initial treatment, with up to 70 percent of tumors shrinking on chemotherapy, and then almost always returns, which is why survival stayed low for so long. Limited stage disease treated with chemotherapy and radiation has a five year survival around 30 percent; extensive stage disease, historically under 5 percent. The recent approvals attack the relapse problem directly. Our lung cancer treatment guide covers the approved options in detail; for the biggest risk factor, see our smoking cessation trials page.
Types of small cell lung cancer clinical trials
Antibody drug conjugate trials. Chemotherapy attached to an antibody that seeks out small cell cancer cells, tested against standard second line chemotherapy in Phase 3.
T cell engager and bispecific trials. Antibodies that pull immune cells onto cancer cells, following tarlatamab, in new combinations and earlier lines.
CAR T cell trials. Early studies of engineered T cells aimed at proteins such as B7-H3 in people whose cancer has returned.
First line and maintenance trials. New drugs added to chemotherapy plus immunotherapy from the start, and treatments to extend the time before relapse.
Limited stage trials. Radiation techniques, including proton therapy, and immunotherapy timing in people treated with the goal of cure.
Biology studies. Tumor sampling and blood based research into why small cell cancer resists treatment, often open to anyone with the diagnosis.
New to research? Read how clinical trials for cancer work.
Who can participate in small cell lung cancer clinical trials?
Trials specify stage and treatment history precisely. First line trials enroll people with newly diagnosed extensive stage disease before any treatment. Relapsed trials, the largest group, enroll people whose cancer returned after platinum chemotherapy, often split by whether it returned within 90 days (platinum resistant) or later. Limited stage trials enroll people around the time of chemoradiation. Most require that you can manage daily activities and have adequate organ function, and many allow treated, stable brain metastases, which are common in this disease. Because the cancer moves fast, screening is usually quick. Eligibility always varies by study; our guide explains eligibility criteria.
The stages of small cell lung cancer, and why they matter for trials
Limited stage. Cancer on one side of the chest, treatable within one radiation field. Treated with chemotherapy and radiation together, followed by durvalumab since 2024, with cure as the goal. About 30 percent of cases.
Extensive stage. Spread beyond one side of the chest or to distant organs. Treated with chemotherapy plus immunotherapy, then maintenance. About 70 percent of cases, and where most new drug trials recruit.
Relapsed. Cancer that returned after first treatment, described as platinum sensitive or resistant by how soon it came back. The setting for T cell engagers, antibody drug conjugates, and CAR T trials.
Study titles use exactly these words. Your stage and the date your cancer last responded to platinum chemotherapy tell you which studies fit.
What is the newest treatment for small cell lung cancer?
Three arrived in 18 months: tarlatamab (Imdelltra), a DLL3 T cell engager approved in May 2024 with full approval in November 2025; durvalumab after chemoradiation for limited stage disease, approved in December 2024; and lurbinectedin with atezolizumab as maintenance, approved in October 2025. Antibody drug conjugates and CAR T cells are in trials.
How to enroll in a small cell lung cancer clinical trial
Identify your trial. Use the filters and start with "small cell," then the stage and line: "extensive stage first line," "relapsed," or "limited stage."
Select your preferred location. Enter your city or state. Phase 3 trials run at dozens of sites including community oncology practices; CAR T trials run at a few centers.
Explore study details. Click "Learn More" for prior treatment requirements, brain metastasis rules, and the visit schedule.
Complete the health profile. Click "Get started" to begin the 5-step application. Have three things ready: your stage, the treatments you have had and when your cancer last responded, and whether you have brain metastases and how they were treated.
Submit the application. A clinical trial coordinator reviews it and contacts you, usually within days. Nothing is decided until informed consent, and participation is voluntary at every step.