The M1 aminopeptidase family is important for the maturation or degradation of bioactive peptides by hydrolyzing their N-terminal amino acids. Some investigators have studied aminopeptidase in the maintenance of homeostasis including maintenance of normal pregnancy, memory retention, blood pressure regulation and antigen presentation. However, there are a few reports on the relation between the M1 aminopeptidase family and carcinoma. In addition to its capacity to degrade a range of peptides, placental-leucine aminopeptidase (P-LAP) has novel functions that impact on normal cells and neoplastic cells. P-LAP is the focus of this review.