Although we found that ALDH1 activity was relatively higher in the established ovarian cancer cell lines compared to primary ovarian tumor specimens (Figure 3B and Figure 4B), we did not find a significant difference in ALDH1 activity between primary isolated tumors and long-term cultures of tumor cell lines from the same ovarian cancer transgenic mouse model (Figure S1), suggesting that the relatively lower ALDH enzymatic activity observed in primary ovarian cancer cells may be due to the procedure of sample collection and preparation. This evidence concerns the gene ALDH1A1 and ovarian cancer.