Imdelltra and Cytokine Release Syndrome: Why Early-dose Monitoring Matters?

Starting a lung cancer treatment often comes with a period of adjustment, but the beginning of treatment can involve an important extra step of close monitoring after the initial doses. For example, with Imdelltra (tarlatamab), patients are monitored closely after the first two doses. This is not because complications are expected, but because cytokine release syndrome (CRS), one of the treatment’s most notable side effects, is most likely to occur during these early doses. ^[1]

This early monitoring is not a reason for concern; rather, it is a planned safety measure that allows healthcare professionals to recognise and manage potential reactions promptly. Hence, understanding why this monitoring matters when receiving Imdelltra can help one feel more prepared and reassured.

What is Imdelltra and how does it work?

Imdelltra, also known as tarlatamab, is a medicine used to treat people with extensive-stage small cell lung cancer (SCLC) whose disease has worsened during or after initial treatment with chemotherapy. SCLC is a type of lung cancer that can grow and spread quickly. Extensive-stage SCLC means that the cancer has spread within the lung or to other parts of the body. ^[2]

Imdelltra works by bringing T cells, which are immune cells that can kill cancer cells, into close contact with lung cancer cells. This helps the T cells recognise and destroy the cancer cells more effectively. ^[3]

What is Cytokine Release Syndrome (CRS)?

Cytokines are immune substances that perform many different functions in the body. ^[4] When released in excessive amounts, they can cause widespread inflammation that may affect organs and tissues. ^[5] Cytokine release syndrome (CRS) occurs when the immune system releases a large amount of cytokines into the bloodstream. Signs and symptoms of CRS include fever, nausea, headache, rash, rapid heartbeat, low blood pressure, and trouble breathing. Most patients have a mild reaction, but sometimes, the reaction may be severe or life-threatening. ^[4]

Why CRS monitoring matters during early dosing of Imdelltra?

In one of the landmark clinical trials of Imdelltra, named as the DeLLphi-301 trial, CRS occurred in 53% patients. CRS occurred predominantly after the first or second dose, more commonly post the first dose. The median time to CRS onset from the first Imdelltra dose was 13.7 hours, with the median time to resolution being 3 days. The CRS profile of Imdelltra was commonly characterised by low-grade events that rarely required immediate intensive interventions or resulted in treatment interruptions or discontinuations. ^[6]

Because the timing and clinical course of CRS were considered predictable and manageable, the post-infusion monitoring period after the first two infusions was reduced from 48-hour inpatient monitoring to 6–8-hour outpatient monitoring. The monitoring period was subsequently reduced further in later trials. ^[1]

For people living with extensive-stage SCLC, this change can mean less time spent in a healthcare setting during the initial treatment period. It may also help reduce some of the practical challenges associated with administering Imdelltra in community oncology settings. ^[7]

What signs and symptoms to look for after taking Imdelltra for suspecting CRS? ^[8]

The signs and symptoms to look for after taking Imdelltra include,

 - fever of 100.4°F (38°C) or higher

 - nausea and vomiting

 - low blood pressure

 - confusion, restlessness, or feeling anxious

 - tiredness

 - problems with balance and movement, such as trouble walking

 - headache

 - heart, liver, or kidney problems

 - shortness of breath or trouble breathing

 - unusual bleeding or bleeding that lasts a long time

 - fast heartbeat or dizziness

Lesser grade or milder version of CRS are more common with Immdeltra, which include symptoms of fever with low oxygen levels and/or low blood pressure that do not require medications. ^[6]

Who is at risk of getting CRS post-Imdelltra?

Clearly defined clinical risk factors for CRS with tarlatamab have not been established, as events occur across a broad range of patient and disease characteristics. Suggested contributors from the broader literature include high tumour burden, inflammation present at baseline, and poor performance status. ^[7]

What happens in early post-dose monitoring?

Early-post dose monitoring of 6 to 8 hours is done from the start of infusion for the first 2 doses.  The monitoring period then decreases to 3–4 hours for Cycles 3 - 4 and 2 hours for Cycle 5 and subsequent doses. Patients should also remain within 1 hour of an appropriate healthcare setting for a total of 48 hours from the start of the infusion after the Cycle 1 Day 1 and Cycle 1 Day 8 doses, accompanied by a caregiver. A follow-up assessment, including vital signs, is also recommended on the day after each of these first two doses, on Cycle 1 Days 2 and 9. ^[8,9]

What other measures are taken to avoid the risk of Imdelltra-induced CRS?

Because of the risk of CRS, Imdelltra is given using a “step-up dosing schedule.” This means:

 - A smaller dose of Imdelltra is given on Day 1 of the first treatment cycle (Cycle 1).

 - The full treatment dose is given on Day 8 and Day 15 of Cycle 1.

 - After Day 15 of Cycle 1, the full treatment dose is given once every 2 weeks.

 - If a dose of Imdelltra is delayed for any reason, the step-up dosing schedule may need to be repeated.

Conclusion:

Imdelltra offers a different kind of treatment for small cell lung cancer, one that harnesses the immune system rather than working through chemotherapy. That same immune activation is what makes the first doses different from every dose after them. Close monitoring during this early window is not a sign of a problem; it is what allows CRS to be caught and managed quickly if it happens, so treatment can continue safely. Your oncology team can walk you through exactly what to expect during those first two doses and beyond.

Medical Disclaimer:

This information is provided for educational purposes only and is not a substitute for professional medical advice. Medicine should only be taken under the guidance of a qualified healthcare provider. Patients should always consult their doctor for advice on diagnosis, treatment, and medication use, and should not make changes to their prescribed therapy without medical supervision.

References:

 - Mountzios, G., Sun, L., for the DeLLphi-304 Investigators, Cho, B. C., Demirci, U., Baka, S., Gümüş, M., Lugini, A., Zhu, B., Yu, Y., Korantzis, I., Han, J. Y., Ciuleanu, T. E., Ahn, M. J., Rocha, P., Mazières, J., Lau, S. C. M., Schuler, M., Blackhall, F., ... Dingemans, A.-M. (2025). Tarlatamab in Small-Cell Lung Cancer after Platinum-Based Chemotherapy. New England Journal of Medicine, 393(4), 349-361.

 - European Medicines Agency. Imdylltra (tarlatamab): EPAR [Internet]. Amsterdam: European Medicines Agency; 2025

 - National Cancer Institute. Tarlatamab-dlle [Internet]. Bethesda (MD): National Cancer Institute; [cited 2026 Sep 25]

 - National Cancer Institute. Cytokine release syndrome [Internet]. Bethesda (MD): National Cancer Institute

 - Cleveland Clinic. Cytokine release syndrome (CRS) [Internet]. Cleveland (OH): Cleveland Clinic

 - Sands JM, Champiat S, Hummel HD, Paulson KG, Borghaei H, Alvarez JB, Carbone DP, Carlisle JW, Choudhury NJ, Clarke JM, Gadgeel SM, Izumi H, Navarro A, Lau SCM, Lammers PE, Huang S, Hamidi A, Mukherjee S, Owonikoko TK. Practical management of adverse events in patients receiving tarlatamab, a delta-like ligand 3-targeted bispecific T-cell engager immunotherapy, for previously treated small cell lung cancer. Cancer. 2025 Feb 1;131(3):e35738.

 - FDA approves reduced monitoring time for first two doses of IMDELLTRA (tarlatamab-dlle) [Internet]. Thousand Oaks (CA): Amgen; 2026 Sep 14

 - S. Food and Drug Administration. IMDELLTRA (tarlatamab-dlle) prescribing information [Internet]. Silver Spring (MD): U.S. Food and Drug Administration; 2024

 - Cheema, P.K.; Perdrizet, K.A.; Sangha, R.S.; Breadner, D.; Daaboul, N.; Farley, S.; Jao, K.; Liu, G.; Logan, B.; Melosky, B.; et al. Early Experience with Tarlatamab (T-Cell Engagers) for Extensive-Stage Small Cell Lung Cancer (ES-SCLC) in Canada: Lessons Learned and Implementation Strategies. Oncol. 2026, 33, 8