L-Asparaginase (ASNase) is a non-human enzyme that hydrolyses the amino acid asparagine (Asn) into aspartic acid and ammonia. It is used in the clinic as a cornerstone drug for the treatment of pediatric leukemia. Evidence is accumulating that ASNase may also have clinical potential for the treatment of certain aggressive solid cancer subtypes, including metastastic breast cancer. However, in adult patients ASNase administration is often associated with immunological side-effects and non-immune related toxicities. Because of the tolerability issues in adults, the clinical potential of ASNase for the treatment of solid cancer subtypes has not been fully pursued. One could speculate that the development of a more tolerable and less immunogenic L-asparaginase (ASNase) variants could drastically improve the outcome of adult leukemia patients, and expand its use to many other aggressive subtypes of human cancer with an overall bad outcome. We recently developed an alternative stabilized mammalian ASNase variant that has no glutaminase co-activity. Our data provides strong evidence that this alternative variant is as efficient in killing cancer cells but has significantly less adverse side-effects as compared to the bacterial pegaspargase that is nowadays used in the clinic. In this project, we will evaluate the therapeutic potential of this less toxic alternative asparaginase for the treatment of metastatic breast cancer.