ALDH1A1 and breast cancer: However, high expression of ALDH1A1 has been associated with resistance to chemotherapy in in vitro studies [43,44,45], and with worse disease-free survival and OS after neoadjuvant chemotherapy in breast cancer [46] The ALDH1A1 enzyme participates in the conversion process of ifosfamide to its active metabolite, by the detoxification of aldoifosfamide.