MKI67 and carcinoid tumor: Uniquely, in five patients (cases A02, A05, A16, A17, and A20), the SCLC histotype was present in metastatic sample(s), whereas primary/intrathoracic sample(s) exhibited a carcinoid histotype, characterized by well-differentiated bland, uniform cells with a lower nuclear-to-cytoplasmic ratio, and Ki67 index of mostly ≤20% (Fig. 1E; Supplementary Figs. S3 and S4A).