A previous study analyzing the DNA methylation profiles of ovarian serous neoplasms indicated that CD40 is hypomethylated in LGSCs compared with SBOTs, suggesting the expression of CD40 may be higher in LGSCs than in SBOTs.26 To test this hypothesis, we examined CD40 expression levels in SBOT-derived SBOT3.1 cells and LGSC-derived MPSC1 cells. Here, CD40 is linked to ovarian serous tumor.