In the context of breast cancer, a study by Zareba et al. in MCF-7 breast cancer cells suggested that Gly-Pro and Gly-Pro-derived proline, along with the level of activity of the enzymes that cleave it (e.g., proline dehydrogenase/proline oxidase and prolidase) may play an intricate role in the balance between apoptosis, autophagy, and the growth of neoplastic cells [80]. Here, PEPD is linked to breast cancer.