TOP2A and squamous cell carcinoma: LCNECs mostly shared similarities with SCLC, revealing upregulation of pathways and genes controlling cell cycle and mitosis (E2F transcription factors and checkpoint kinases), DNA damage response (RAD51, TOP2A, and BRCA1) and centrosomal functions (such as BUB1, PLK1, and ASPM); which, to some extent, were also found in squamous cell carcinomas (Fig. 2b; Supplementary Fig. 8g–i, Supplementary Data 13–14), and which is in agreement with previous studies18.