Mechanism of cancer pain

Current studies of acupuncture in cancer-induced bone pain animal models

Acupuncture is generally accepted as a safe and harmless treatment option for alleviating pain. To explore the pain mechanism, numerous animal models have been developed to simulate specific human pain conditions, including cancer-induced bone pain (CIBP). In this study, we analyzed the current research methodology of acupuncture for the treatment of CIBP. We electronically searched the PubMed database for animal studies published from 2000 onward using these search terms: (bone cancer OR cancer) AND (pain OR analgesia) AND (acupuncture OR pharmacopuncture OR bee venom). We selected articles that described cancer pain in animal models. We analyzed the methods used to induce cancer pain and the outcome measures used to assess the effects of acupuncture on CIBP in animal models. We reviewed articles that met our inclusion criteria. Injection of mammary cancer cells into the cavity of the tibia was the most frequently used method for inducing CIBP in the animal models. Among the eight selected studies, five studies demonstrated the effects of electroacupuncture on CIBP. The effects of acupuncture were assessed by measuring pain-related behavior. Future researches will be needed to ascertain the effectiveness of acupuncture for treating CIBP and to explore the specific mechanism of CIBP in animal models.

ProNGF correlates with Gleason score and is a potential driver of nerve infiltration in prostate cancer

Nerve infiltration is essential to prostate cancer progression, but the mechanism by which nerves are attracted to prostate tumors remains unknown. We report that the precursor of nerve growth factor (proNGF) is overexpressed in prostate cancer and involved in the ability of prostate cancer cells to induce axonogenesis. A series of 120 prostate cancer and benign prostate hyperplasia (BPH) samples were analyzed by IHC for proNGF. ProNGF was mainly localized in the cytoplasm of epithelial cells, with marked expression in cancer compared with BPH. Importantly, the proNGF level positively correlated with the Gleason score (n = 104, τB = 0.51). A higher level of proNGF was observed in tumors with a Gleason score of ≥8 compared with a Gleason score of 7 and 6 (P < 0.001). In vitro, proNGF was detected in LNCaP, DU145, and PC-3 prostate cancer cells and BPH-1 cells but not in RWPE-1 immortalized nontumorigenic prostate epithelial cells or primary normal prostate epithelial cells. Co-culture of PC12 neuronal-like cells or 50B11 neurons with PC-3 cells resulted in neurite outgrowth in neuronal cells that was inhibited by blocking antibodies against proNGF, indicating that prostate cancer cells can induce axonogenesis via secretion of proNGF. These data reveal that ProNGF is a biomarker associated with high-risk prostate cancers and a potential driver of infiltration by nerves.

cGMP and cGMP-dependent protein kinase I pathway in dorsal root ganglia contributes to bone cancer pain in rats

STUDY DESIGN

A prospective, randomized experimental research.

OBJECTIVE

To demonstrate the role of cGMP (cyclic guanosine monophosphate)-cGKI (cGMP-dependent protein kinase I) pathway in dorsal root ganglia (DRG) in bone cancer pain.

SUMMARY OF BACKGROUND DATA

Treating bone cancer pain continues to possess a major clinical challenge because the specific cellular and molecular mechanisms underlying bone cancer pain remain elusive. cGMP and cGMP-dependent protein kinases pathway in DRG plays important role in nerve injury-induced hyperexcitability of DRG neurons, as well as neuropathic pain, however, whether this pathway participates in bone cancer pain is unknown.

METHODS

The rat model of bone cancer pain was produced by intramedullary injection of rat breast cancer cells (Walker 256) into right tibia. Thermal hyperalgesia and mechanical allodynia were measured before and after administration of inhibitor of cGMP-cGKs pathway (Rp-8-pCPT-cGMPS). Immunofluorescence and reverse transcription-polymerase chain reaction were used to reflect expression of cGKI in DRG neurons, whereas the concentration of cGMP in DRG was tested using enzyme-linked immunosorbent assay method. Whole-cell patch clamp was used to record the hyperexcitability of small neurons in DRG with or without cGKs inhibitor after tumor cell implantation (TCI).

RESULTS

TCI treatment significantly increased the concentration of cGMP in DRG and activity of cGKs in DRG and the spinal cord. TCI treatment also induced upregulation of cGKI messenger ribonucleic acid and protein in DRG, as well as enhanced hyperexcitability in DRG neurons. Spinal administration of Rp-8-pCPT-cGMPS, cGMP-cGKs inhibitor, significantly suppressed TCI-induced activation of cGMP-cGKI signaling, and hyperexcitability of DRG neurons. Meanwhile, in vivo intrathecal delivery of the Rp-8-pCPT-cGMPS significantly prevented and suppressed TCI-induced hyperalgesia and allodynia.

CONCLUSION

From these results, we confirm that TCI treatment activates cGMP-cGKI signaling pathway and continuing activation of this pathway in DRG is required for hyperalgesia and/or hyperalgesia and allodynia after TCI treatment.

LEVEL OF EVIDENCE

N/A.

Pain in the cancer patient: different pain characteristics CHANGE pharmacological treatment requirements

Twenty years ago, the main barriers to successful cancer pain management were poor assessment by physicians, and patients' reluctance to report pain and take opioids. Those barriers are almost exactly the same today. Cancer pain remains under-treated; in Europe, almost three-quarters of cancer patients experience pain, and almost a quarter of those with moderate to severe pain do not receive any analgesic medication. Yet it has been suggested that pain management could be improved simply by ensuring that every consultation includes the patient's rating of pain, that the physician pays attention to this rating, and a plan is agreed to increase analgesia when it is inadequate. After outlining current concepts of carcinogenesis in some detail, this paper describes different methods of classifying and diagnosing cancer pain and the extent of current under-treatment. Key points are made regarding cancer pain management. Firstly, the pain may be caused by multiple different mechanisms and therapy should reflect those underlying mechanisms - rather than being simply based on pain intensity as recommended by the WHO three-step ladder. Secondly, a multidisciplinary approach is required which combines both pharmacological and non-pharmacological treatment, such as psychotherapy, exercise therapy and electrostimulation. The choice of analgesic agent and its route of administration are considered, along with various interventional procedures and the requirements of palliative care. Special attention is paid to the treatment of breakthrough pain (particularly with fast-acting fentanyl formulations, which have pharmacokinetic profiles that closely match those of breakthrough pain episodes) and chemotherapy-induced neuropathic pain, which affects around one third of patients who receive chemotherapy. Finally, the point is made that medical education should place a greater emphasis on pain therapy, both at undergraduate and postgraduate level.

Relationship of inflammatory markers and pain in patients with head and neck cancer prior to anticancer therapy

Pain is a common symptom in patients with cancer, including those with head and neck cancer (HNC). While studies suggest an association between chronic inflammation and pain, levels of inflammatory cytokines, such as C-reactive protein (CRP) and tumor necrosis factor-alpha (TNF-α), have not been correlated with pain in HNC patients who are not currently undergoing anticancer treatment. The purpose of this study was to examine the relationship between these inflammatory markers and perceived pain in HNC patients prior to anticancer therapy. The study group consisted of 127 HNC patients and 9 healthy controls. Pain was assessed using the Brief Pain Inventory (BPI), and serum levels of CRP and TNF-α were determined using the particle-enhanced turbidimetric immunoassay (PETIA) and ELISA techniques, respectively. Patients experiencing pain had significantly higher levels of CRP (P<0.01) and TNF-α (P<0.05) compared with controls and with patients reporting no pain. There were significantly positive associations between pain, CRP level, and tumor stage. This is the first study to report a positive association between perceived pain and CRP in HNC patients at the time of diagnosis. The current findings suggest important associations between pain and inflammatory processes in HNC patients, with potential implications for future treatment strategies.

Involvement of spinal PKA/CREB signaling pathway in the development of bone cancer pain

BACKGROUND

It has been shown that spinal PKA/CREB signaling pathway is involved in neuropathic and inflammatory pain, but its effects on bone cancer pain have not previously been investigated. The aim of this study was to examine the potential role of the spinal PKA/CREB signaling pathway in the development of bone cancer pain.

METHODS

A bone cancer pain model was made by inoculation of Walker 256 cells into the intramedullary space of rat tibia. Western blot analysis examined the expression of PKAca (PKA catalytic subunit) and phospho-CREB (p-CREB) protein levels. The authors further investigated effects of intrathecal treatment with H-89 (a PKA inhibitor, 8 nmol) or forskolin (a PKA agonist, 10 nmol) on nociceptive behavior and the expression of PKAca and p-CREB.

RESULTS

On days 6, 9, and 15 after inoculation, the expression of PKAca and p-CREB protein levels were higher in the bone cancer pain rats compared to the sham rats. On day 9, intrathecal administration of H-89 significantly attenuated bone cancer-induced mechanical allodynia as well as upregulation of PKAca and p-CREB protein levels. These effects were completely abolished by intrathecal pretreatment with the PKA agonist forskolin.

CONCLUSION

The results suggest that the spinal PKA/CREB signaling pathway may participate in the development of bone cancer pain. The findings of this study may provide an evidence for developing novel analgesics to block bone cancer pain.

Recent advances in cancer pain management

Pain is the most feared symptom of cancer. New oncological cancer treatments are improving survival, but advanced cancer presents challenges that have not been seen before, often with pain that is very difficult to manage because of a recurrent tumour that is invading the central nervous system. In some of the older interventional techniques of destroying nerve pathways, expertise has diminished or has been deemed unnecessary with the development of specialist palliative care. Not all pain is managed adequately with the analgesic ladder. Knowledge of pain mechanisms, careful assessment and selection of the right technique at the right time will enhance cancer pain management. New techniques include intrathecal drug therapy, vertebroplasty, cordotomy, ultra-sound guided nerve blocks, neuromodulation and advances in drug therapies.

An overview of animal models of pain: disease models and outcome measures

Pain is ultimately a perceptual phenomenon. It is built from information gathered by specialized pain receptors in tissue, modified by spinal and supraspinal mechanisms, and integrated into a discrete sensory experience with an emotional valence in the brain. Because of this, studying intact animals allows the multidimensional nature of pain to be examined. A number of animal models have been developed, reflecting observations that pain phenotypes are mediated by distinct mechanisms. Animal models of pain are designed to mimic distinct clinical diseases to better evaluate underlying mechanisms and potential treatments. Outcome measures are designed to measure multiple parts of the pain experience, including reflexive hyperalgesia measures, sensory and affective dimensions of pain, and impact of pain on function and quality of life. In this review, we discuss the common methods used for inducing each of the pain phenotypes related to clinical pain syndromes as well as the main behavioral tests for assessing pain in each model.

PERSPECTIVE

Understanding animal models and outcome measures in animals will assist in translating data from basic science to the clinic.

Analgesic efficacy and mode of action of a selective small molecule angiotensin II type 2 receptor antagonist in a rat model of prostate cancer-induced bone pain

OBJECTIVE

The pathobiology of prostate cancer (PCa)-induced bone pain (PCIBP) has both inflammatory and neuropathic components. Previously, we showed that small molecule angiotensin II type 2 receptor (AT2 R) antagonists with >1,000-fold selectivity over the angiotensin II type 1 receptor produced dose-dependent analgesia in a rat model of neuropathic pain. Here, we assessed the analgesic efficacy and mode of action of the AT2 R antagonist, EMA200, in a rat model of PCIBP.

METHODS

At 14-21 days after unilateral intratibial injection of AT3B PCa cells, rats exhibiting hindpaw hypersensitivity received single intravenous bolus doses of EMA200 (0.3-10 mg/kg) or vehicle, and analgesic efficacy was assessed. The mode of action was investigated using immunohistochemical, Western blot, and/or molecular biological methods in lumbar dorsal root ganglia (DRGs) removed from drug-naïve and EMA200-treated PCIBP rats relative to sham-control rats.

RESULTS

Intravenous bolus doses of EMA200 produced dose-dependent analgesia in PCIBP rats. Lumbar DRG levels of angiotensin II, nerve growth factor (NGF), tyrosine kinase A (TrkA), phospho-p38 mitogen-activated protein kinase (MAPK), and phospho-p44/p42 MAPK, but not the AT2 R, were increased significantly (P < 0.05) in PCIBP rats, c.f. the corresponding levels for sham controls. EMA200 produced analgesia in PCIBP rats by reducing elevated angiotensin II levels in the lumbar DRGs to attenuate augmented angiotensin II/AT2 R signaling. This in turn reduced augmented NGF/TrkA signaling in the lumbar DRGs. The net result was inhibition of p38 MAPK and p44/p42 MAPK activation.

CONCLUSION

Small molecule AT2 R antagonists are worthy of further investigation as novel analgesics for relief of intractable PCIBP and other pain types where hyperalgesia worsens symptoms.

Pathobiology and management of prostate cancer-induced bone pain: recent insights and future treatments

Prostate cancer (PCa) has a high propensity for metastasis to bone. Despite the availability of multiple treatment options for relief of PCa-induced bone pain (PCIBP), satisfactory relief of intractable pain in patients with advanced bony metastases is challenging for the clinicians because currently available analgesic drugs are often limited by poor efficacy and/or dose-limiting side effects. Rodent models developed in the past decade show that the pathobiology of PCIBP comprises elements of inflammatory, neuropathic and ischemic pain arising from ectopic sprouting and sensitization of sensory nerve fibres within PCa-invaded bones. In addition, at the cellular level, PCIBP is underpinned by dynamic cross talk between metastatic PCa cells, cellular components of the bone matrix, factors associated with the bone microenvironment as well as peripheral components of the somatosensory system. These insights are aligned with the clinical management of PCIBP involving use of a multimodal treatment approach comprising analgesic agents (opioids, NSAIDs), radiotherapy, radioisotopes, cancer chemotherapy agents and bisphosphonates. However, a major drawback of most rodent models of PCIBP is their short-term applicability due to ethical concerns. Thus, it has been difficult to gain insight into the mal(adaptive) neuroplastic changes occurring at multiple levels of the somatosensory system that likely contribute to intractable pain at the advanced stages of metastatic disease. Specifically, the functional responsiveness of noxious circuitry as well as the neurochemical signature of a broad array of pro-hyperalgesic mediators in the dorsal root ganglia and spinal cord of rodent models of PCIBP is relatively poorly characterized. Hence, recent work from our laboratory to develop a protocol for an optimized rat model of PCIBP will enable these knowledge gaps to be addressed as well as identification of novel targets for drug discovery programs aimed at producing new analgesics for the improved relief of intractable PCIBP.

Protease-activated receptor 2 in dorsal root ganglion contributes to peripheral sensitization of bone cancer pain

BACKGROUND

Treating bone cancer pain continues to be a major clinical challenge, and the underlying mechanisms of bone cancer pain remain elusive. Protease-activated receptor 2 (PAR2) has been reported to be involved in neurogenic inflammation, nociceptive pain and hyperalgesia. Here, we investigated the role of PAR2 in bone cancer pain development.

METHORDS

Expression of PAR2, mechanical allodynia, thermal hyperalgesia and neurochemical alterations induced by bone cancer pain were analysed in male, adult C3H/HeJ mice with tumour cell implantation (TCI). To investigate the contribution of PAR2 to bone cancer pain, PAR2 antagonist peptide and PAR2 knockout mice were used.

RESULTS

TCI produced bone cancer-related pain behaviours. Production and persistence of these pain behaviours were well correlated with TCI-induced up-regulation of PAR2 in sciatic nerve and dorsal root ganglia (DRG). PAR2 knockout and spinal administration of PAR2 antagonist peptide prevented and/or reversed bone cancer-related pain behaviours and associated neurochemical changes in DRG and dorsal horn (DH). TCI also induced proteases release in tumour-bearing tibia, sciatic nerve and DRG. Plantar injection of supernatant from sarcoma cells induced PAR2 up-regulation and intracellular calcium [Ca(2+) ]i increase in DRG, and calcitonin gene-related peptide accumulation in DH, as well as significant thermal and mechanical hyperalgesia, which were all in PAR2-dependent manners.

CONCLUSION

These findings suggest that PAR2 may be a key mediator for peripheral sensitization of bone cancer pain. Inhibiting PAR2 activation, especially during the early phase, may be a new therapy for preventing/suppressing development of bone cancer pain.

Involvement of spinal CC chemokine ligand 5 in the development of bone cancer pain in rats

In this study, we aimed to investigate the role of spinal CC chemokine ligand 5 (CCL5) in the development of bone cancer pain (BCP). A BCP model was established by inoculation of Walker 256 cells into the intramedullary space of rat tibia. The levels of spinal CCL5 mRNA and protein expression significantly and time dependently increased in BCP rats compared with sham rats. On day 15 after inoculation, intrathecal administration of anti-CCL5 neutralizing antibody (4 μg) significantly attenuated the established mechanical hyperalgesia in the Walker 256 cells-injected rats, and the effect was abolished by intrathecal pre-treatment with recombinant rat CCL5 (0.2 μg). These results suggest that the spinal CCL5 may be involved in the development of BCP. The findings of this study may provide an evidence for developing novel analgesic agents to treat BCP.

Spinal RhoA/Rho kinase signalling pathway may participate in the development of bone cancer pain

It has been shown that activation of spinal RhoA/Rho kinase (ROCK) signalling pathway facilitates nociception in neuropathic and inflammatory pain, but its effects on bone cancer pain (BCP) have not previously been studied. This study was designed to examine the potential role of the spinal RhoA/ROCK signalling pathway in the development of BCP. A model for bone cancer was induced by injecting Walker 256 cells into the tibia of rats. On days 6, 9 and 15 after inoculation, the expression of spinal RhoA and ROCK2 protein levels was higher in the Walker 256 cells injected rats compared to the sham rats. On day 9, intrathecal injection of C3 exoenzyme (a RhoA inhibitor, 10 pg) significantly attenuated BCP behaviour as well as up-regulation of spinal RhoA and ROCK2 protein levels. These effects were completely abolished by intrathecal pretreatment with U-46619 (a RhoA agonist, 1.5 pg). These results suggest that the spinal RhoA/ROCK signalling pathway may be involved in the development of BCP. The findings of this study may lead to novel therapeutic strategies for prevention and/or treatment of BCP.

Spinal cord stimulation for cancer-related pain in adults

BACKGROUND

Cancer-related pain places a heavy burden on public health with related high expenditure. Severe pain is associated with a decreased quality of life in patients with cancer. A significant proportion of patients with cancer-related pain are under-treated.There is a need for more effective control of cancer-related pain. Spinal cord stimulation (SCS) may have a role in pain management. The effectiveness and safety of SCS for patients with cancer-related pain is currently unknown.

OBJECTIVES

This systematic review evaluated the effectiveness of SCS for cancer-related pain compared with standard care using conventional analgesic medication. We also appraised risk and potential adverse events associated with the use of SCS.

SEARCH METHODS

We searched the following bibliographic databases in order to identify relevant studies: the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Libary (from inception to 2012, Issue 6); MEDLINE; EMBASE; and CBM (Chinese Biomedical Database) (from inception to July, 2012). We also handsearched relevant journals.

SELECTION CRITERIA

We planned to include randomised controlled trials (RCTs) that directly compared SCS with other interventions with regards to the effectiveness of pain management. We also planned to include cross-over trials that compared SCS with another treatment. We planned to identify non-randomised controlled trials but these would only be included if no RCTs could be found.

DATA COLLECTION AND ANALYSIS

The initial search strategy yielded 430 articles. By scrutinising titles and abstracts, we found 412 articles irrelevant to the analytical purpose of this systematic review due to different scopes of diseases or different methods of intervention (intrathecal infusion system; oral medication) or aims other than pain control (spinal cord function monitoring, bladder function restoration or amelioration of organ metabolism). The remaining 18 trials were reviewed as full manuscripts. No RCTs were identified. Fourteen sporadic case reports and review articles were excluded and four before-and-after case series studies (92 participants) were included. Two review authors independently selected the studies to be included in the review according to the pre-specified eligibility criteria. A checklist for methodological quality of non-randomised controlled trials was used (STROBE checklist) and all review authors discussed and agreed on the inclusion of trials and the results of the quality assessment.

MAIN RESULTS

Four before-and-after case series studies (a total of 92 participants) met our criteria for inclusion. All included trials adopted a visual analogue scale (VAS) to evaluate pain relief. Heterogeneity existed in terms of baseline characteristics, electrode and stimulator parameters, level of implantation and route of implantation; data reporting was different among all trials. In two trials, pain relief was achieved in 76% (48/63) of patients at the end of the follow-up period. In the third trial, pre-procedure VAS was 6 to 9 (mean 7.43 ); the one-month post-implant VAS was 2 to 4 (mean 3.07); the 12-month post-implant VAS was 1 to 3 (mean 2.67). In the fourth trial, the pre-procedure VAS was 6 to 9 (mean 7.07); 1 to 4 (mean 2.67) at one-month; 1 to 4 (mean 1.87) at 12 months. Analgesic use was largely reduced. The main adverse events were infection of sites of implantation, cerebrospinal fluid (CSF) leakage, pain at the sites of electrodes, dislodgement of the electrodes and system failure, however, the incidence in patients with cancer could not be calculated. Since all trials were non-randomised controlled trials, they carried risk of all types of bias.

AUTHORS' CONCLUSIONS

Current evidence is insufficient to establish the role of SCS in treating refractory cancer-related pain. Future randomised studies should focus on the implantation of SCS in patients with cancer-related pain.

Biomarkers: symptoms, survivorship, and quality of life

OBJECTIVES

To review the evidence on a number of biomarkers that show potential clinical utility in the prediction of and treatment responsiveness for the four most common symptoms associated with cancer and its treatment (ie, pain, fatigue, sleep disturbance, depression).

DATA SOURCES

Review and synthesis of review articles and data-based publications.

CONCLUSION

A growing body of evidence suggests that sensitive and specific biomarkers will be available to assist clinicians with the assessment and management of symptoms.

IMPLICATIONS FOR NURSING PRACTICE

Nurses will play a critical role in educating patients about their risk for specific symptoms based on an evaluation of specific biomarkers. Nurses will be involved in using biomarker data to titrate medications based on patient's responses to symptom management interventions.

Surveying proteolytic processes in human cancer microenvironments by microdialysis and activity-based mass spectrometry

PURPOSE

We present a strategy to survey proteolytic processes that occur in human cancer microenvironments.

EXPERIMENTAL DESIGN

In situ microdialysis during oral cancer surgery was combined with mass spectrometry-based proteomics to analyze interstitial fluid surrounding tumors and anatomically matched normal sites. Protease activity-based (18)O-profiling was utilized to reveal peptides that were processed by co-collected proteases ex vivo.

RESULTS

We demonstrated for the first time the use of microdialysis in humans to collect interstitial fluid from cancer microenvironments. Proteomic profiling identified proteases and inhibitors in the microdialysis samples. A subset of peptides displayed characteristic (18)O-isotope patterns that indicated processing by endogenous proteases.

CONCLUSIONS AND CLINICAL RELEVANCE

The presented approach provides unprecedented views of in vivo targets of proteases without disrupting the cancer or surrounding tissue. The methodology can be broadly adapted to other physiological conditions in which proteolytic mediators are involved (e.g. arthritic joints, inflamed muscle, other types of cancer) and where a comparison of normal and pathological tissue is sought.

Activation of spinal TDAG8 and its downstream PKA signaling pathway contribute to bone cancer pain in rats

Bone cancer pain is difficult to treat and has a strong impact on the quality of life of patients. Few therapies have emerged because the molecular mechanisms underlying bone cancer pain are poorly understood. Recently, T-cell death-associated gene 8 (TDAG8) has been shown to participate in complete Freund's adjuvant-induced chronic inflammatory pain. In this study, we aimed to examine whether TDAG8 and its downstream protein kinase A (PKA) pathway are involved in bone cancer pain. A bone cancer pain model was made by inoculation of Walker 256 cells into the intramedullary space of rat tibia. Spinal TDAG8 expression was increased after inoculation with tumor cells. Intrathecal TDAG8 siRNA attenuated bone cancer pain behaviors during the initiation and maintenance phases; there were also concomitant decreases in TDAG8 mRNA and protein levels in spinal cord. Moreover, we found spinal PKA and phosphorylated cAMP response element-binding (pCREB) protein levels were up-regulated in the rat model of bone cancer pain. Knockdown of TDAG8 resulted in reduced bone cancer pain-induced spinal PKA and pCREB protein expression in two procedures. Furthermore, intrathecal H-89 (a PKA inhibitor) significantly attenuated bone cancer pain behaviors in rats. Our results suggest a causal relationship between TDAG8 expression and the initiation and maintenance of bone cancer pain. Activation of spinal TDAG8 contributes to bone cancer pain through the PKA signaling pathway in rats. These findings may lead to novel strategies for the treatment of bone cancer pain.

Head and neck cancer pain: systematic review of prevalence and associated factors

OBJECTIVES

Pain is a major symptom in patients with cancer; however information on head and neck cancer related pain is limited. The aim of this review was to investigate the prevalence of pain and associated factors among patients with HNC.

MATERIAL AND METHODS

The systematic review used search of MEDLINE, EMBASE and CINAHL databases to December 2011. Cancers of the oral mucosa, oropharynx, hypopharynx and larynx were included in this review with pain as main outcome. The review was restricted to full research reports of observational studies published in English. A checklist was used to assess the quality of selected studies.

RESULTS

There were 82 studies included in the review and most of them (84%) were conducted in the past ten years. Studies were relatively small, with a median of 80 patients (IQR 44, 154). The quality of reporting was variable. Most studies (77%) used self-administered quality of life questionnaires, where pain was a component of the overall scale. Only 33 studies reported pain prevalence in HNC patients (combined estimate from meta-analysis before (57%, 95% CI 43% - 70%) and after (42%, 95% CI 33% - 50%) treatment. Only 49 studies (60%) considered associated factors, mostly tumour- or treatment-related.

CONCLUSIONS

The study has shown high levels of pain prevalence and some factors associated with higher levels of pain. There is a need for higher quality studies in a priority area for the care of patients with head and neck cancer.

Distinct time courses of microglial and astrocytic hyperactivation and the glial contribution to pain hypersensitivity in a facial cancer model

Although recent evidence suggests that central glial hyperactivation is involved in cancer-induced persistent pain, the time course of this hyperactivation and the glial contribution to pain hypersensitivity remain unclear. The present study investigated the time-dependent spatial changes of microglial and astrocytic hyperactivation in the trigeminocervical complex, which consists of the medullary (MDH) and upper cervical (UCDH) dorsal horns, and pain-related behaviors in a rat facial cancer model in which Walker 256B-cells are inoculated into the vibrissal pad. In this model, the tumors grew within the vibrissal pad, from which sensory nerve fibers project into the MDH, but did not expand into the infraorbital region, from which fibers project into the UCDH. Nevertheless, mechanical allodynia and thermal hyperalgesia were observed not only in the vibrissal pad but also in the infraorbital region. Western blotting and immunofluorescence studies indicated that microglia were widely activated in the trigeminocervical complex on day 4 and gradually inactivated by day 11. In contrast, astrocytes were only activated in the MDH on day 4; the hyperactivation later expanded into the UCDH. Daily administration of the glial hyperactivation inhibitor propentofylline beginning on day 4 suppressed the glial hyperactivation on later days. Propentofylline treatment largely prevented allodynia/hyperalgesia in the infraorbital region beginning on day 5, although established allodynia/hyperalgesia in the vibrissal pad was less sensitive to the treatment. These results suggest that central glial hyperactivation, transient microglial hyperactivation and persistent astrocytic hyperactivation, contributes to the development of pain hypersensitivity but not to the maintenance of pain in this model.

The effects of electroacupuncture at the ST36 (Zusanli) acupoint on cancer pain and transient receptor potential vanilloid subfamily 1 expression in Walker 256 tumor-bearing rats

BACKGROUND

Several studies have addressed the expression of transient receptor potential vanilloid subfamily 1(TRPV1) playing an important role in the generation of cancer pain. Electroacupuncture (EA) is an effective method of acupuncture shown to attenuate different kinds of pain such as inflammatory, neuropathic, and cancer. In this study, we investigated the effect of EA on cancer pain caused by intraplantar injection of Walker 256 carcinoma cells and cancer-driven TRPV1 expression in the dorsal root ganglions (DRGs).

METHODS

Rats were randomly divided into 4 groups: the nontumor cell inoculation group (normal control, n = 8); Walker 256 carcinoma cell inoculation group (tumor control, n = 8); sham point electrical stimulation treatment with Walker 256 carcinoma cell inoculation group (SES, n = 8); EA treatment with Walker 256 carcinoma cell inoculation group (EA, n = 8). The time courses of thermal, mechanical sensitivity, and spontaneous nocifensive behavior were determined. In addition, TRPV1 expression in DRGs was observed by quantitative real-time polymerase chain reaction and Western blotting.

RESULTS

Injection of cancer cells decreased the paw withdrawal threshold, increased spontaneous nocifensive behavior, and induced significant thermal hyperalgesia that was attenuated by EA at the ST36 acupoint (2 Hz, 0.3 ms, ≤1 mA). TRPV1 mRNA and protein in DRGs were upregulated in the cancer pain model, and EA at ST36 acupoint counteracted the cancer-driven upregulation of TRPV1 expression in the corresponding DRGs.

CONCLUSIONS

EA at ST36 could attenuate cancer-induced pain, at least in part, through suppressing TRPV1 mRNA and protein upregulation in the DRGs.

Cancer Pain: A Critical Review of Mechanism-based Classification and Physical Therapy Management in Palliative Care

Mechanism-based classification and physical therapy management of pain is essential to effectively manage painful symptoms in patients attending palliative care. The objective of this review is to provide a detailed review of mechanism-based classification and physical therapy management of patients with cancer pain. Cancer pain can be classified based upon pain symptoms, pain mechanisms and pain syndromes. Classification based upon mechanisms not only addresses the underlying pathophysiology but also provides us with an understanding behind patient's symptoms and treatment responses. Existing evidence suggests that the five mechanisms – central sensitization, peripheral sensitization, sympathetically maintained pain, nociceptive and cognitive-affective – operate in patients with cancer pain. Summary of studies showing evidence for physical therapy treatment methods for cancer pain follows with suggested therapeutic implications. Effective palliative physical therapy care using a mechanism-based classification model should be tailored to suit each patient's findings, using a biopsychosocial model of pain.

Biologic mechanisms of oral cancer pain and implications for clinical therapy

Cancer pain is an ever-present public health concern. With innovations in treatment, cancer patients are surviving longer, but uncontrollable pain creates a poor quality of life for these patients. Oral cancer is unique in that it causes intense pain at the primary site and significantly impairs speech, swallowing, and masticatory functions. We propose that oral cancer pain has underlying biologic mechanisms that are generated within the cancer microenvironment. A comprehensive understanding of key mediators that control cross-talk between the cancer and peripheral nervous system, and possible interventions, underlies effective cancer pain management. The purpose of this review is to explore the current studies on oral cancer pain and their implications in clinical management for cancer pain in general. Furthermore, we will explore the endogenous opioid systems and novel cancer pain therapeutics that target these systems, which could solve the issue of opiate tolerance and improve quality of life in oral cancer patients.

Preventive or late administration of anti-NGF therapy attenuates tumor-induced nerve sprouting, neuroma formation, and cancer pain

Early, preemptive blockade of nerve growth factor (NGF)/tropomyosin receptor kinase A (TrkA) attenuates tumor-induced nerve sprouting and bone cancer pain. A critical unanswered question is whether late blockade of NGF/TrkA can attenuate cancer pain once NGF-induced nerve sprouting and neuroma formation has occurred. By means of a mouse model of prostate cancer-induced bone pain, anti-NGF was either administered preemptively at day 14 after tumor injection when nerve sprouting had yet to occur, or late at day 35, when extensive nerve sprouting had occurred. Animals were humanely killed at day 70 when, in vehicle-treated animals, significant nerve sprouting and neuroma formation was present in the tumor-bearing bone. Although preemptive and sustained administration (days 14-70) of anti-NGF more rapidly attenuated bone cancer nociceptive behaviors than late and sustained administration (days 35-70), by day 70 after tumor injection, both preemptive and late administration of anti-NGF significantly reduced nociceptive behaviors, sensory and sympathetic nerve sprouting, and neuroma formation. In this model, as in most cancers, the individual cancer cell colonies have a limited half-life because they are constantly proliferating, metastasizing, and undergoing necrosis as the parent cancer cell colony outgrows its blood supply. Similarly, the sensory and sympathetic nerve fibers that innervate the tumor undergo sprouting at the viable/leading edge of the parent tumor, degenerate as the parent cancer cell colony becomes necrotic, and resprout in the viable, newly formed daughter cell colonies. These results suggest that preemptive or late-stage blockade of NGF/TrkA can attenuate nerve sprouting and cancer pain.