The mu-Opioid Receptor in Cancer and Its Role in Perineural Invasion: A Short Review and New Evidence

Cancer is a significant public health problem worldwide. While there has been a steady decrease in the cancer death rate over the last two decades, the number of survivors has increased and, thus, cancer-related sequela. Pain affects the life of patients with cancer and survivors. Prescription opioids continue as the analgesic of choice to treat moderate-to-severe cancer-related pain. There has been controversy on whether opioids impact cancer progression by acting on cancer cells or the tumor microenvironment. The mu-opioid receptor is the site of action of prescription opioids. This receptor can participate in an important mechanism of cancer spread, such as perineural invasion. In this review, current evidence on the role of the mu-opioid receptor in cancer growth is summarized and preliminary evidence about its effect on the cross-talk between sensory neurons and malignant cells is provided.