In this case report, the choice of natural cycle FET was primarily based on the following considerations: Although CA125 is not a specific biomarker for endometriosis, it was used in these cases as a non-specific marker to monitor disease activity and treatment response rather than diagnostic purposes (24), and postoperative normalization of CA125 levels in these two cases might indicate effective inflammation control. The gene discussed is MUC16; the disease is endometriosis.