Ifinatamab Deruxtecan Shows Promising Activity in Previously Treated Extensive‑Stage SCLC: Primary Analysis of Phase II IDeate‑Lung01

Highlight

– Ifinatamab deruxtecan (I‑DXd), a B7‑H3–directed antibody‑drug conjugate (ADC), produced a confirmed objective response rate (ORR) of 48.2% in previously treated ES‑SCLC (12 mg/kg every 3 weeks).

– Median progression‑free survival (PFS) was 4.9 months and median duration of response (DOR) 5.3 months; 9‑month overall survival estimate 59.1%.

– Safety signals mirror those seen with other deruxtecan payload ADCs: high rates of hematologic toxicities and an adjudicated treatment‑related interstitial lung disease (ILD) rate of 12.4% (grade ≥3, 4.4%).

Background: disease burden and unmet need

Small cell lung cancer (SCLC) comprises ~15% of lung cancers and is characterized by rapid growth, early metastasis, and an initial sensitivity to cytotoxic chemotherapy. Despite initial responses, most patients with extensive‑stage disease (ES‑SCLC) relapse rapidly and have poor longer‑term outcomes. First‑line treatment now commonly includes platinum‑etoposide plus a PD‑L1 inhibitor (for example, atezolizumab or durvalumab), which modestly extended overall survival in randomized trials, but durable benefit remains uncommon.

Therapeutic options in the relapsed setting are limited. Approved or commonly used second‑line options include topotecan, lurbinectedin, and rechallenge with platinum‑based regimens in selected patients, but response rates are modest and median progression‑free intervals are short. There is therefore an urgent need for new agents with novel mechanisms that can produce clinically meaningful responses in previously treated ES‑SCLC.

Study design

IDeate‑Lung01 is a phase II trial that evaluated I‑DXd, an antibody‑drug conjugate that targets B7 homolog 3 (B7‑H3, also known as CD276), a cell‑surface immunoregulatory protein variably expressed across solid tumors including SCLC. The cytotoxic payload is a topoisomerase I inhibitor delivered through a cleavable linker, a design concept shared with other deruxtecan ADCs.

The trial had two parts. Part 1 randomized patients to dose optimization (I‑DXd 8 mg/kg or 12 mg/kg IV every 3 weeks). Part 2 was an extension cohort in which patients received I‑DXd 12 mg/kg every 3 weeks. Eligible patients had previously treated ES‑SCLC with a median of two prior lines of therapy.

The primary endpoint was objective response rate (ORR) assessed by blinded independent central review according to RECIST v1.1. Key secondary endpoints included duration of response (DOR), progression‑free survival (PFS), overall survival (OS) estimates, and safety, with ILD adjudication performed centrally.

Key findings

Population and dosing

In total, 183 patients received I‑DXd: 88 in part 1 (46 at 8 mg/kg, 42 at 12 mg/kg) and 95 in part 2 (12 mg/kg). The primary analysis focuses on the pooled 12 mg/kg group across parts 1 and 2 (n = 137). Patients were heavily pretreated (median 2 prior lines).

Efficacy

In the pooled 12 mg/kg cohort (n = 137) the confirmed ORR was 48.2% (95% CI, 39.6–56.9). Median time to response was rapid at 1.4 months (range, 1.0–8.1). Median duration of response was 5.3 months (95% CI, 4.0–6.5), and median progression‑free survival was 4.9 months (95% CI, 4.2–5.5). The 9‑month overall survival estimate was 59.1%.

These activity measures compare favorably with historical benchmarks for single‑agent therapies in the relapsed ES‑SCLC setting. For context, the single‑agent lurbinectedin phase II study reported an ORR of ~35% and median PFS of ~3.5 months in a similar population. The higher ORR and somewhat longer PFS with I‑DXd are encouraging, particularly given the heavily pretreated nature of the study population. The rapid onset of responses (median time 1.4 months) is consistent with cytotoxic ADC activity.

Safety

Overall, treatment‑related adverse events (TRAEs) of any grade occurred in 89.8% of patients (grade ≥3, 36.5%). The most frequent TRAEs were nausea (43.1%), anemia (34.3%), and neutropenia (34.3%). Treatment discontinuations due to TRAEs occurred in 9.5% of patients, and treatment‑related deaths were reported in 4.4%.

Of particular note, treatment‑related interstitial lung disease (ILD) adjudicated by the ILD committee occurred in 12.4% of patients, with grade ≥3 ILD in 4.4%. The ILD frequency is clinically important and aligns with the known pulmonary toxicity observed with other ADCs that carry topoisomerase I inhibitor payloads, notably trastuzumab deruxtecan in breast and lung cancer studies.

Interpretation and clinical context

The primary analysis of IDeate‑Lung01 shows that B7‑H3‑targeted delivery of a deruxtecan payload can lead to substantial antitumor activity in a disease historically refractory to multiple lines of therapy. A confirmed ORR near 50% in previously treated ES‑SCLC is notable and suggests that I‑DXd could meaningfully expand therapeutic options if efficacy is confirmed in randomized settings.

Nevertheless, the safety profile requires careful attention. Hematologic toxicity and gastrointestinal adverse events are expected with topoisomerase I‑containing payloads and were common here, but generally manageable with supportive measures and dose modifications. The adjudicated ILD rate of 12.4% is especially important: although most events were low‑grade, a subset were severe and treatment‑related deaths were reported. ILD is a recognized class effect for deruxtecan payload ADCs and mandates proactive monitoring, early symptom recognition, prompt discontinuation, and institution of glucocorticoids when indicated.

Strengths and limitations

Strengths of the trial include blinded independent central review of response and centralized ILD adjudication, which strengthen the validity of efficacy and safety assessments. The inclusion of a dose‑optimization phase adds useful dose‑response safety data supporting the 12 mg/kg schedule.

Key limitations are the nonrandomized nature of the efficacy evaluation for the pivotal 12 mg/kg cohort (part 2 was an extension cohort), absence of a contemporary control arm, and limited information on biomarker correlates. B7‑H3 expression in SCLC is heterogeneous; it remains unclear whether expression level predicts response to I‑DXd, and whether tissue or circulating biomarkers could improve patient selection. Central nervous system (CNS) activity was not emphasized in the primary report and warrants further study given SCLC’s propensity for brain metastases.

Biologic plausibility and mechanism

B7‑H3 (CD276) is an immunoregulatory molecule overexpressed in multiple solid tumors and is associated with poor prognosis in some malignancies. Targeting B7‑H3 with an antibody‑drug conjugate enables selective delivery of a potent topoisomerase I inhibitor to tumor cells while potentially sparing normal tissues. This method builds on the clinical experience with deruxtecan ADCs in breast and other cancers, which have demonstrated robust tumor responses but also yielded class‑specific toxicities including ILD.

Implications for practice and next steps

For practicing oncologists, the IDeate‑Lung01 results are an early proof of concept that B7‑H3 ADCs can be active in relapsed ES‑SCLC. Before adopting I‑DXd in routine care, confirmatory randomized data comparing against standard second‑line options (for example, topotecan or lurbinectedin where available) are needed to define relative benefit and net clinical advantage.

Future trial priorities should include randomized controlled trials, exploration of combination regimens (for example, pairing ADCs with immune or targeted agents), biomarker development to identify likely responders (tumor B7‑H3 expression, circulating tumor DNA signatures), CNS activity assessments, and prospective ILD mitigation strategies including baseline pulmonary evaluation and standardized monitoring algorithms.

Expert commentary

Leading clinicians and researchers have highlighted two consistent themes for ADCs in SCLC: (1) ADCs that leverage tumor‑selective antigens offer a promising therapeutic strategy in an otherwise treatment‑refractory tumor, and (2) the balance between efficacy and pulmonary toxicity will determine the clinical adoption of deruxtecan‑payload ADCs. The adjudicated ILD signal in IDeate‑Lung01, while not unique to this agent, underscores the need for clear monitoring and management pathways if the drug proceeds toward regulatory review.

Conclusion

The phase II IDeate‑Lung01 primary analysis indicates that ifinatamab deruxtecan 12 mg/kg every 3 weeks produces encouraging antitumor activity in previously treated ES‑SCLC, with a confirmed ORR of 48.2% and median PFS of 4.9 months. Safety findings are consistent with deruxtecan‑containing ADCs, notably an adjudicated treatment‑related ILD rate of 12.4% that requires vigilant monitoring. These data support further randomized evaluation and biomarker development to establish the therapeutic role of I‑DXd in ES‑SCLC.

Funding and clinicaltrials.gov

Details on trial funding, sponsor, and clinicaltrials.gov registration are provided in the primary manuscript: Rudin CM et al., J Clin Oncol. 2025. Readers should consult the published article for full declarations.

References

1) Rudin CM, Johnson ML, Paz‑Ares L, et al. Ifinatamab Deruxtecan in Patients With Extensive‑Stage Small Cell Lung Cancer: Primary Analysis of the Phase II IDeate‑Lung01 Trial. J Clin Oncol. 2025 Oct 14:JCO2502142. doi: 10.1200/JCO‑25‑02142. Epub ahead of print. PMID: 41086386 IF: 41.9 Q1 B1.

2) Horn L, Mansfield AS, Szczesna A, et al. First‑line atezolizumab plus carboplatin and etoposide in extensive‑stage small‑cell lung cancer. N Engl J Med. 2018;379(23):2220–2229.

3) Paz‑Ares L, Dvorkin M, Chen Y, et al. Durvalumab plus platinum‑etoposide vs platinum‑etoposide in first‑line extensive‑stage small‑cell lung cancer (CASPIAN): a randomised, controlled, open‑label, phase 3 trial. Lancet. 2019;394(10212):1929–1939.

4) Trigo J, Subbiah V, Besse B, et al. Lurbinectedin in patients with small‑cell lung cancer: a single‑arm, open‑label, phase 2 basket trial. Lancet Oncol. 2020;21(5):645–654.

5) Picarda E, Ohaegbulam KC, Zang X. Molecular pathways: targeting B7‑H3 (CD276) for human cancer immunotherapy. Clin Cancer Res. 2016;22(14):3425–3431.

6) Modi S, Saura C, Yamashita T, et al. Trastuzumab deruxtecan in previously treated HER2‑positive breast cancer. N Engl J Med. 2020;382(7):610–621.