Accordingly, this review aims to update the findings regarding the involvement of opioid peptides (enkephalins, endorphins, and dynorphins) in cancer development (e.g., mitogenesis, metastasis, angiogenesis); to suggest anticancer therapeutic strategies targeting the opioid peptidergic system (e.g., using opioid-receptor antagonists) and to highlight the main research lines to be developed in the future focused on the involvement of enkephalins, endorphins, and dynorphins in tumor development and progression. Here, PDYN is linked to neoplasm.