Quantitative real-time PCR revealed that BRCA1, RAD51, BIRC5, CDC6, E2F1, MCM4, CDC20, TUBA4A, TUBG1, CCNA1, CCNB1, CCNA2, CHEK1, TOPBP1, MAD2L1, CDT1, HIST3H3, CDK1, BLM, CCNE1, and UBE2C were significantly downregulated in patients with SCOS, compared with normal patients (Fig. 3A). Here, MCM4 is linked to small cell osteogenic sarcoma.