Human arylamine N-acetyltransferase 1 (NAT1) is a phase II xenobiotic-metabolizing enzyme (XME) involved in the biotransformation of many aromatic and heterocyclic amines. This XME plays key roles in both the detoxification and/or bioactivation of numerous drugs and carcinogens. NAT1 is polymorphic and displays a large tissue distribution. NAT1 activity has been extensively studied because of its potential role in the biotransformation of important carcinogens. Several recent studies suggest that NAT1 may have a role in breast cancer progression. Indeed, this XME has been shown to affect the growth and drug resistance of breast cancer cells and appears as a marker in human estrogen receptor positive breast cancer. In addition, it has been shown that this enzyme is inhibited in vivo by cancer drugs such as cisplatin or tamoxifen. Recent published data suggest that NAT1 could be of therapeutic interest for cancer. We provide here an overview on the putative involvement of NAT1 in cancer and its possible role as a drug target.