Consistent with the reports in multiple types of tumors [34], [37], [38], [40], [41], [42], [43], we found that higher percentage of ALDH1 positive tumor cells is significantly associated with poor clinical outcome in serous ovarian cancer (Figure 2D, n = 439, p = 0.0036). The gene discussed is ALDH1A1; the disease is ovarian serous adenocarcinoma.