Introduction

Small cell lung cancer has trailed its non-small cell counterpart in new drug approvals for years, and at this year's ASCO meeting there were no studies presented that affect first-line treatments at this time. There were two developments presented that were worth attention: early but encouraging data on a new antibody-drug conjugate for relapsed disease, and a transcriptomic analysis that, perhaps more usefully, shows what current biomarkers cannot yet do.

A SEZ6-Targeted ADC Shows Activity After Platinum Failure

Seizure-related homolog 6 (SEZ6) is a neuroendocrine-lineage marker expressed at levels and a frequency comparable to DLL3, the target already exploited by other small cell lung cancer therapies. ABBV-706 pairs a SEZ6-directed antibody with a topoisomerase-1 inhibitor payload, and a phase 1 trial (NCT05599984) evaluated it both as monotherapy and in combination with budigalimab, an anti-PD-1 antibody, in patients with relapsed or refractory extensive-stage small cell lung cancer.

The study enrolled patients with an ECOG performance status of 0 or 1 who had received prior platinum-based chemotherapy, excluding those with interstitial lung disease, pulmonary fibrosis, or organizing pneumonia, given the known class risks of antibody-drug conjugates. Monotherapy dose optimization resulted in a dose of 1.8 mg/kg every three weeks, continued until progression or toxicity; the combination arm paired the same dose with budigalimab on the same schedule.

Of 124 total patients, the median age was in the mid-60s, roughly a decade younger than a typical VA population, which is worth keeping in mind when extrapolating these results to older or more comorbid patients. Most had received one or two prior lines of therapy, a majority were platinum-refractory (a chemotherapy-free interval under three months in 61 percent), and rates of brain and liver metastases were high, reflecting an advanced, heavily pretreated population.

Efficacy was strongest in the second-line, 1.8 mg/kg monotherapy cohort: an objective response rate of 82 percent, median progression-free survival of 6.8 months, and median overall survival of 14.3 months. Across the full monotherapy population at that dose, the objective response rate was 56 percent, with a median overall survival of 12.4 months. The combination with budigalimab, tested in a smaller cohort, produced a progression-free survival of 8.1 months with overall survival not yet reached. Toxicity was predominantly hematologic and gastrointestinal: over half of patients had anemia, more than 40 percent had grade 3 anemia, and roughly 20 percent had grade 3 cytopenias, findings likely to shape how this drug is dosed and monitored if it advances toward approval.

What Transcriptomic Subtyping in IMforte Does, and Does Not, Tell Clinicians

The current standard for extensive-stage small cell lung cancer is platinum-etoposide chemotherapy with immunotherapy continued as maintenance until progression or intolerance. The phase 3 IMforte trial tested whether adding lurbinectedin to atezolizumab maintenance improves outcomes compared with atezolizumab alone, and a transcriptomic analysis presented this year described whether any biomarker predicts which patients benefit most.

Pretreatment tumor samples were classified into the recognized small cell lung cancer molecular subtypes (SCLC-A, SCLC-N, and SCLC-I (divided in to neuroendocrine and non-neuroendocrine subgroups); the rare SCLC-P subtype was excluded), alongside gene signatures for tumor-associated macrophage activity and T-effector activity, and expression of SLFN11, a marker previously linked to chemotherapy and PARP-inhibitor sensitivity.

The result: progression-free and overall survival benefit from adding lurbinectedin favored the combination regardless of molecular subtype, meaning no subtype identified a group that benefited disproportionately, or not at all. A signal toward improved overall survival in patients with high tumor-associated macrophage activity did not reach statistical significance, with confidence intervals crossing 1. SLFN11 expression showed no predictive value for outcome in this analysis.

In practice, this means the decision to add lurbinectedin to maintenance atezolizumab remains a discussion grounded in performance status, tolerance of continued therapy, and patient preference, not a biomarker-driven choice. Some sites do not currently offer this option as a pathway default, based partly on concern that the atezolizumab-alone control arm outperformed prior historical expectations in this trial, which complicates interpretation of the absolute benefit. Where it is offered, most patients who have already completed four rounds of chemotherapy are, understandably, may be reluctant to take on more; the trial's own results were positive, but real-world uptake is likely to be modest until a biomarker or a more tolerable regimen changes that calculus for some patients with a poorer performance status or significant co-morbidities.

For Patients

An antibody-drug conjugate works like a targeted delivery system: an antibody finds a protein on the surface of cancer cells and carries a chemotherapy payload directly to them, aiming to spare more of the healthy tissue nearby. The SEZ6-targeted drug described here is still investigational and is not yet approved for general use, but early results in patients whose small cell lung cancer had stopped responding to standard chemotherapy are encouraging enough to watch closely, and patients whose disease has progressed after first-line treatment may want to ask their oncologist about clinical trial availability. Separately, for patients currently on or considering maintenance immunotherapy after initial chemotherapy, no genetic or molecular test yet exists to predict who benefits most from adding a second maintenance drug; that decision is, for now, a personal one to work through with a care team rather than one guided by a tumor's genetic or molecular profile.

Key Takeaways

  • ABBV-706, a SEZ6-targeted antibody-drug conjugate, showed an 82 percent response rate and 14.3-month median overall survival in a second-line monotherapy cohort of relapsed small cell lung cancer, though the data remain early-phase.

  • Hematologic toxicity, particularly anemia and cytopenias, was the most significant safety signal and will likely shape future dosing strategies.

  • A transcriptomic analysis of the phase 3 IMforte trial found that no molecular subtype, macrophage or T-effector signature, or SLFN11 expression level predicted differential benefit from adding lurbinectedin to atezolizumab maintenance.

  • Benefit from lurbinectedin plus atezolizumab appeared consistent across molecular subgroups, meaning the treatment decision currently rests on clinical judgment and patient preference rather than biomarker selection.

  • Unlike the oncogene-driven precision now available in non-small cell lung cancer, small cell lung cancer still lacks a validated biomarker to guide maintenance therapy choices.

References

  1. Byers LA, et al. ABBV-706 as monotherapy and in combination with budigalimab in patients with relapsed/refractory small cell lung cancer. Presented ASCO 2026, Abstract 8008.

  2. Cooper AJ, et al. SEZ6-targeting antibody-drug conjugate ABBV-706 in advanced small cell lung cancer and solid tumors: a phase 1 trial. Nat Med. 2026.

  3. Paz-Ares LG, et al. Transcriptomic analyses of molecular subsets and correlations with clinical outcomes from the phase 3 IMforte study of lurbinectedin plus atezolizumab maintenance treatment in extensive-stage small-cell lung cancer. Presented ASCO 2026, Abstract 8014.

  4. Gay CM, et al. Patterns of transcription factor programs and immune pathway activation define four major subtypes of small cell lung cancer with distinct therapeutic vulnerabilities. Cancer Cell. 2021.