The integration of tarlatamab, a bispecific T-cell engager molecule targeting both DLL3 and CD3, into the treatment algorithm for SCLC will substantially improve the prognosis of patients. Nevertheless, disease progression will inevitably occur.
Major challenges for further improving tarlatamab therapy are the molecular understanding of resistance to tarlatamab and the selection of the optimal systemic therapy upon progression. Patients who experience platinum-sensitive progression more than 90 days after first-line chemoimmunotherapy (platinum-free interval (PFI) = day of last administration of platinum-containing chemotherapy until progression) and subsequently progress on tarlatamab therapy may benefit from a platinum-based chemotherapy re-challenge while remaining on tarlatamab treatment. We hypothesize that patients who progress while on tarlatamab may benefit more from the combination of both therapies than from sequential therapy due to synergistic effects. We assume that, besides the cytotoxic effects of platinumbased chemotherapy, additional T-cell modifying effects could support this concept. The disruption of the tumor stroma, which has been described in various chemotherapies, could increase T-cell infiltration and thus have additional immunostimulatory effects (Hoff et al., 2011). The lymphodepletion triggered by chemotherapy and the resulting release of interleukins such as IL-15 could also have an enhancing effect on therapy with bispecific T-cell engagers (Kochenderfer et al., 2017). In addition, it has been shown preclinically that chemotherapeutic agents that have an inhibitory effect on topoisomerase (e.g. doxorubicin) also have a selective inhibitory effect on MDSCs. Here, the administration of the topoisomerase inhibitor etoposide could counteract possible resistance mechanisms (Alizadeh et al., 2014). Different cut-off values for chemotherapy-sensitive progression in small cell lung cancer between 60 - 90 days PFI have been discussed for decades. It has been shown that a platinum re-challenge as a second chemotherapy regimen is superior in a patient population with a PFI greater than 90 days compared to topotecan (Baize et al., 2020). This is expected to apply to approximately 40% of patients receiving standard first-line platinum-based therapy with PD-L1 inhibitors (Torsawa et al., 2023). If tarlatamab is added to first-line therapy in the near future, the proportion of patients with a PFI of more than 90 days could increase further. In the future, platinum-containing chemotherapy could become an increasingly important role as second-line chemotherapy. In parallel with the clinical evaluation of the re-challenge concept, we will conduct an extensive rebiopsy program. This will include a re-biopsy during progression to tarlatamab therapy at screening and a re-biopsy at the time of progression to the study treatment. Whole exome sequencing and transcriptomic analyses of tumor bulks as well as transcriptomic analysis at the single-cell level will be performed to elucidate molecular mechanisms of resistance in the tumor cells and in the tumor microenvironment. Additional immunohistochemical