TP53 and neoplasm: Belotecan’s longer OS in patients with more advanced disease may be partially due to its higher anti-tumour potency,4 particularly in tumours rich in TP53 mutations.18 It is well-established that advanced SCLC has high levels of TP53 mutation.19,20 Our subgroup OS analyses imply that the patient’s baseline characteristics may indicate whether belotecan would be preferable to topotecan on an individual basis.