We found that the mRNA expression of RRM1, RRM2, and RRM2B genes were up-regulated in 57.9% (11 of 19), 78.9% (15 of 19), and 0% (0 of 9), respectively, of the Oncomine cancer studies covering the four subtypes of LUSC, LUAD, large cell lung carcinoma (LCLC), and small cell lung carcinoma (SCLC) (Figure 4A). Here, RRM1 is linked to small cell lung carcinoma.