RRM2 and small cell lung carcinoma: Firstly, the mRNA expression levels of CDC20, BUB1, TOP2A, RRM2, CCNA2, UBE2C, MAD2L1, and BUB1B were significantly increased in SCLC samples compared with normal lung samples based on the Oncomine database, which was consistent with the above bioinformatics investigation (Fig 7).