Abstract
Tarlatamab is a novel bispecific T-cell engager immunotherapy that has demonstrated efficacy against small-cell lung cancer (SCLC) in terms of noteworthy anticancer activity and survival outcomes. However, no studies have detailed the patterns of disease progression during tarlatamab treatment. Herein, we present a case of acute disease progression after tarlatamab initiation in a 71-year-old male patient with extensive-stage SCLC. Following tarlatamab administration, he developed symptoms of cognitive impairment, which raised suspicion of immune effector cell-associated neurotoxicity syndrome (ICANS), an adverse event associated with the drug. Diagnostic evaluation revealed that the symptoms were caused by obstructive hydrocephalus due to worsening brain metastases. Following tarlatamab administration, we observed rapid progression of the previously indolent SCLC, leading to deterioration in the patient's overall condition. This case highlights the need to consider the possibility of rapid disease progression following tarlatamab administration and underscores the importance of adequate assessment to exclude ICANS. Since rapid tumor progression may lead to a decline in the patient's general condition, careful follow-up is advised.