Tarlatamab population survival kinetics in extensive-stage small cell lung cancer: brief report

Immune checkpoint inhibitors (ICIs) prolong progression-free survival (PFS) and overall survival (OS) in extensive-stage small cell lung cancer (ES-SCLC). ES-SCLC PFS curve exponential decay nonlinear regression analyses (EDNLRAs) suggests that only 10% of patients benefit. Here we report ES-SCLC EDNLRAs for the bispecific T-cell engager tarlatamab.

We digitized tarlatamab ES-SCLC PFS and OS curves from published studies and performed EDNLRAs of curve data.

All four PFS curves fit 2-phase decay models, suggesting the presence of two distinct subpopulations- one with a short PFS half-life (median 3.2 months, similar to the tarlatamab DeLLphi-304 study chemotherapy arm) and the other with a very long PFS half-life). EDNLRAs indicated that 88 % of the patients belonged to the rapidly progressing subpopulation. The proportion of patients in the subpopulation with long PFS was lower than the study response rates. However, log-linear plots of response-duration curves also suggested 2-phase decay, with one subpopulation having very long responses and the other having very short responses. Two of four OS curves assessed fit 2-phase decay models. Longer follow-up will be required to assess the other two curves. For curves fitting 2-phase decay models, OS half-life for the subpopulation with shorter OS was modestly longer than the OS for the Dellphi-304 chemotherapy arm.

In ES-SCLC, EDNLRA of tarlatamab PFS curves and log-linear plots of response duration curves suggest two distinct subpopulations- one deriving marked benefit from tarlatamab and the other deriving much less benefit. Individual patient data might provide insight into underlying driving factors.