Paravertebral anesthesia: how substance P and the NK-1 receptor could be involved in regional block and breast cancer recurrence

Abstract

In a retrospective study, Exadaktylos et al. [1] reported a beneficial relationship between paravertebral block and cancer recurrence in women undergoing mastectomy and axillary clearance for breast cancer. In fact, these authors concluded that ‘‘breast cancer patients undergoing surgery with paravertebral anesthesia and analgesia combined with general anesthesia have a lower incidence of cancer recurrence or metastasis during the initial years of followup than patients undergoing surgery with general anesthesia and patient-controlled morphine analgesia’’ [1]. These authors speculated that regional anesthesia might attenuate the perioperative factors that enhance tumor growth and spreading [1]. In this sense, regional anesthesia may help to maintain normal perioperative immune function by attenuating the surgical stress response by blocking noxious inputs mediated by substance P [2]. It is known that the stress response induces an inhibition of the immune function (i.e., there is a marked attenuation of natural killer cells, these cells being involved in preventing tumor dissemination) [3]. Paravertebral anesthesia also spares patients from postoperative opioids (e.g., morphine), which inhibit both cellular and humoral immune function [4, 5]; in addition, it is known that morphine exerts a proangiogenic effect [6]. In sum, the authors surmised that regional anesthesia and analgesia may help to preserve immune function by attenuating the surgical stress response and diminishing the need for opioids. However, until now the underlying mechanisms remain unknown. The reason for this letter is to provide additional data that could support and explain the relationship between regional anesthesia, analgesia, and the recurrence of cancer. Many reports have clearly established an overexpression of neurokinin-1 (NK-1) receptors in tumor cells and others have reported the roles in which substance P (SP) is involved [7]. Summing up these investigations, it could be stated that: