This study brings another ingredient to the broad discussion on the relationship between opioids and cancer. This study is unprecedented in the literature in analyzing the interference of intraoperative opioid dose on survival in patients with Glioblastoma Multiforme. We obtained results that confirmed the lack of correlation between intraoperative opioid dose and overall survival and disease-free survival in patients with Glioblastoma Multiforme.
In a study similar to ours, Cata et al. analyzed the use of intraoperative opioids in 195 patients with Squamous Cell Carcinoma of the Larynx[19] and noted an association with worsened survival but with low clinical relevance. The same author similarly analyzed this possible relationship with Non-Small Cell Lung Cancer[20] in 901 patients and reported a decline in survival only in those with stage I disease, concluding that there is insufficient evidence to discontinue the use of opioids in these surgeries.
In 2010 Forget, P. et al. published an article in which they analyzed the influence of several intraoperative analgesics used in mastectomies for breast cancer on disease recurrence. The opioid analyzed in this study was sufentanil, which showed no interference with recurrence[21]. In a preclinical study in mice, Doornebal et al. concluded that morphine did not facilitate the progression and dissemination of lobular, invasive, and HER2 + breast cancer [22].
The perioperative period causes cancer patients to experience extreme immunological vulnerability owing to several factors, including surgical stress with the release of catecholamines and prostaglandins, resulting in intense inflammation, hypothermia, tissue damage, blood transfusions, nutritional imbalance, and the use of anesthetics and analgesics, among which opioids play a relevant role[23, 24].
The interaction of these drugs in the evolution of malignant neoplasms can occur in two ways: directly through opioid µ receptors (ROM) in tumor cells and indirectly by inhibiting the immune system. This interference may occur directly in immunocytes (which also express ROM) or through the hypothalamic-pituitary system[25].
Zhang et al. demonstrated that ROM is a risk factor for metastasis in esophageal squamous cell carcinoma[26]. Another in vitro study revealed that hepatocarcinoma cells showed reduced proliferation due to inhibition of the opioid receptor µ [27]. Singleton et al. analyzed histopathological samples of lung cancer from individuals with and without metastases and identified a significantly higher expression of ROM in the former, suggesting a direct effect of this receptor on tumor progression[28]. In lung cancer, Mathew et al. concluded in an in vitro study that opioids, through the evident increase in ROM in neoplastic cells, stimulate tumor growth, a fact that was opposed when methylnaltrexone, an opioid antagonist, was used.
In a basic study on mice with breast cancer, Nguyen et al. concluded that morphine promotes tumor growth by increasing ROM expression(DOORNEBAL et al., 2015). Moreover, in a study published in 2015, the authors listed several studies showing a direct relationship between increased expression of the µ receptor in tumor cells and tumor dissemination and studies showing the action of an opioid antagonist (methylnaltrexone) as an inhibitor of tumor growth[29]. Specifically, regarding opioid antagonists as possible therapeutic targets in the control of various types of malignancies, Belltall et al. published a review and found that most studies were preclinical; therefore, there is insufficient evidence for this conclusion[30].
Regarding the immune system, Forget et al. analyzed the interaction between various analgesics and individual conditions in rats. The animals were subjected to surgery (laparotomy), and the activity of natural killer (NK) cells, which are responsible for the first line of defense of cellular immunity, was quantified at various times during the perioperative period. Fentanyl, the only opioid included, was shown to be a major inhibitor of NK activity and the only drug with a propensity to increase the incidence of metastasis (clonidine and ketamine were also included in this analysis) [21]. In this context, Beilin et al. published a prospective randomized study of 40 patients who underwent surgery with high and low doses of fentanyl. Both groups showed impaired NK cell activity; however, the first group recovered this function much later[31].
Liang et al. reviewed the topic of opioids and immune function and concluded that publications show antagonistic actions of these drugs. In their final analysis, the authors reported that, in general, opioids at low doses over a short time tend to stimulate the immune system. Immunosuppressive effects are associated with high doses and prolonged exposure [32].
In contrast, Gaspani et al. concluded in a rat study that tramadol acts as an immunostimulator, increasing the activity of NK cells, which does not occur with morphine. Tramadol is a centrally acting analgesic with low affinity for the µreceptor (GASPANI et al., 2002). Analyzing the same drugs, Sacerdote et al. reported similar results in a clinical study of patients undergoing surgery for uterine cancer; tramadol had a stimulatory effect on the immune system, while morphine acted in the opposite way[11].
In an extensive review on the action of opioid receptors on the immune system, Eisenstein TK. reported that morphine acts as an immunosuppressant most of the time and that this action is blocked by opioid antagonists through ROM[34].
The interest of the scientific community in the various implications of opioids, besides the complexity of the pharmacokinetics of these drugs, was stimulated by the so-called "opioid crisis" that broke out in the United States in the early 1990s. At that time, the American population showed an alarming number of deaths due to the abuse of opioid drugs indiscriminately prescribed in that country. The combination of these negative factors - inhibition of the immune system, interference in the prognosis of malignant neoplasms, and the North American public health crisis–has led to increased research on opioid-free anesthesia and the advantages of regional anesthesia over general anesthesia[9, 17, 32].
In this line of investigation, Exadaktylos et al. retrospectively analyzed 129 patients with breast cancer regarding recurrence and metastases in two groups, one undergoing mastectomy with paravertebral anesthesia and analgesia combined with general anesthesia and the other with general anesthesia and analgesia with morphine. They obtained significantly positive results in the prognosis of the group with paravertebral anesthesia in the first 30 months of follow-up[35].
In a brief review on the subject, Sessler D. I. lists three factors related to the decline in cellular immunity resulting from cancer surgery: stress due to tissue injury, general anesthesia, and opioid analgesia. In his evaluation, based mainly on preclinical in vitro and in vivo studies, these factors generated both impaired cellular immunity and increased angiogenesis, favoring tumor recurrence. This tendency is minimized by locoregional anesthesia and opioid-free analgesia[36].
In another review, Snyder et al. reported the effects of several anesthetic and analgesic drugs used in general anesthesia on the immune system. Specifically, the authors emphasized the inhibition of NK cell activity induced by morphine and fentanyl. Antagonistically, tramadol promotes the stimulation of these cells, providing an antitumor action[37].
Bovill, in an editorial, warns that, even though the evidence is inconclusive and conflicting, the option of loco-regional anesthesia should be considered whenever possible, minimizing the use of opioids. His conclusion is based on several studies that suggest not only an immunosuppressive influence but also the possibility of inducing tumorigenesis provided by general anesthesia and analgesia with opioids[38].
Cata et al. published an extensive review on how regional anesthesia would benefit and how general anesthesia would be detrimental to patients undergoing cancer surgery. The article didactically illustrates the pro-and antitumor actions of several factors and drugs and concludes that there is still not enough evidence to state that regional anesthesia reduces the risk of recurrence after cancer surgery[39]. The same conclusion was published by a group of experienced authors from the College of Anesthesiologists of Ireland on the topic of cancer and anesthesia, in which, among other statements, they attested the intriguing relationship between the use of opioid anesthetics and prognosis after neuro-oncological surgery [40].
Regarding gliomas and anesthetic techniques, Sung et al. addressed the topic in a retrospective study of 230 patients undergoing first surgery for glioma divided into two groups: one undergoing scalp block with local anesthetic after induction of anesthesia and the other without block. The group with scalp block showed longer disease-free survival than the group without a block. Importantly, this study also included patients with Grade II and III gliomas(SUNG et al.2021). In this study, no interference of opioids on patient prognosis was observed.
In a comprehensive review of the influence of anesthetic and analgesic techniques on GBM progression, Privorotskiy et al. reported that opioids do not affect survival after surgery for this tumor[42].
Two in vitro studies reported the apoptotic effects of opioids on glioma cells. Xu et al. concluded that remifentanil induces apoptosis in glioma cells, and Brawanski et al. showed that high doses of D- and L-methadone have apoptotic effects on glioblastoma cells and interact with temozolomide, the main chemotherapeutic agent used in the treatment of GBM[43]. Friesen et al. reported that D-methadone, acting as a µ-receptor agonist, inhibited the growth of GBM cells[44].
Finally, a recently published review by Ramirez et al. revealed the controversial and inconclusive topic of opioids and cancer prognosis, showing that the relationship between these two entities holds both favorable and unfavorable results [45].