We found that CD55+ cells isolated from cisplatin-naive (A2780, TOV112D, PDX) and cisplatin-resistant (CP70, HEC1a) endometrioid tumor cells were significantly more self-renewing than their CD55− counterparts (stem cell frequencies for CD55+ vs. CD55− were 1 in 2.2 vs. 1 in 4.3 in A2780 [P < 0.01], 1 in 10.8 vs. 1 in 59.2 in TOV112D [P < 0.001], 1 in 36 vs. 1 in 87.7 in PDX [P < 0.05], 1 in 1.4 vs. 1 in 5.1 in CP70 [P < 0.001], and 1 in 59.6 vs. 1 in 209.7 in HEC1a [P < 0.01]; Fig. 1 F and Fig. S1 H). This evidence concerns the gene CD55 and endometrioid tumor.