In addition, KEGG enrichment analysis revealed that the upregulated pathways included the ubiquitin-mediated proteolysis, progesterone-mediated oocyte maturation, protein processing in the endoplasmic reticulum and small cell lung cancer, and downregulated pathways included the calcium signaling pathway, glucagon signaling pathway and insulin signaling pathway had a close relationship with the DE-circRNAs in HO samples. This evidence concerns the gene GCG and small cell lung carcinoma.