Lucan · Conditions

Cancer pain management

Australian guidance: eTG Palliative Care + eTG Pain & Analgesia + CareSearch

1. Definition and epidemiology

Cancer pain is pain arising directly from tumour invasion, metastatic disease, or treatment-related tissue damage in a person with a diagnosed malignancy. It affects approximately 55% of patients receiving anticancer treatment and up to 66% of patients with advanced or metastatic cancer, making it one of the most prevalent and undertreated symptoms in oncology. In Australia, cancer remains a leading cause of disease burden, with over 165,000 new diagnoses annually, meaning that effective pain management is a core competency across primary care, oncology, and palliative services.

2. Pathophysiology

Cancer pain is mechanistically heterogeneous and rarely involves a single pathway. Nociceptive somatic pain arises when tumour directly invades or compresses bone, muscle, or connective tissue, activating peripheral nociceptors via prostaglandins, bradykinin, and substance P released at sites of tissue destruction. Nociceptive visceral pain occurs when tumour stretches or infiltrates hollow organs or their capsules, producing poorly localised, cramping, or referred pain mediated through autonomic afferents. Neuropathic pain results from direct tumour compression or infiltration of peripheral nerves, nerve roots, or the spinal cord, producing burning, shooting, or allodynic pain driven by ectopic discharge, central sensitisation, and loss of inhibitory interneurons. Treatment-related pain adds further mechanisms: chemotherapy-induced peripheral neuropathy involves length-dependent axonal degeneration; post-surgical pain involves neuroma formation and scar tethering; radiation fibrosis compresses adjacent neural structures. In advanced disease, inflammatory cytokines such as interleukin-1 beta and tumour necrosis factor alpha lower peripheral nociceptor thresholds and drive central sensitisation, amplifying all pain subtypes simultaneously.

3. Clinical presentation and diagnostic criteria

The clinical presentation of cancer pain depends on the dominant mechanism and site. Bone metastases classically produce constant background pain with incident pain on weight-bearing or movement, often worse at night. Visceral pain from hepatic capsule distension, bowel obstruction, or peritoneal involvement is typically cramping, poorly localised, and associated with nausea and autonomic features. Neuropathic components manifest as burning or electric-shock quality pain, with allodynia or hyperalgesia on examination. Assessment must quantify pain intensity using a validated scale (Numerical Rating Scale 0 to 10 or the Abbey Pain Scale for cognitively impaired patients), identify the pain mechanism, determine the temporal pattern (background vs incident), and evaluate functional impact and psychosocial distress. The eTG Palliative Care chapter recommends using a structured tool such as the Brief Pain Inventory or a palliative-specific assessment instrument at each encounter. A new or escalating pain in a patient with known cancer requires urgent clinical reassessment to exclude oncological emergencies such as spinal cord compression, pathological fracture, or bowel obstruction.

4. Investigations and AU-specific cutoffs

Initial investigation is guided by the clinical question. Plain X-ray of the symptomatic region can identify gross bony destruction but lacks sensitivity for early metastatic disease. CT scanning of the chest, abdomen, and pelvis is the standard staging and reassessment modality and should be performed with contrast unless contraindicated. Whole-body bone scan or PET-CT is preferred when multifocal skeletal metastases are suspected. MRI of the spine is the gold-standard investigation when spinal cord compression is suspected; this is a clinical emergency requiring same-day imaging. Serum investigations relevant to pain management include full blood count (to detect anaemia exacerbating fatigue and pain perception), renal function (to guide opioid dose selection and metabolite accumulation), liver function tests (relevant to hepatic metastases and drug metabolism), and calcium (hypercalcaemia of malignancy requires correction before pain management is optimised). No single serum cutoff governs analgesic prescribing, but an estimated glomerular filtration rate below 30 mL/min/1.73m2 requires avoidance of renally cleared opioid metabolites such as morphine-6-glucuronide; fentanyl or buprenorphine are preferred in this setting per eTG Pain and Analgesia guidance.

5. Management

Cancer pain management follows the World Health Organization analgesic ladder adapted to an Australian palliative care context, with three steps corresponding to mild, moderate, and severe pain. Early referral to a specialist palliative care service improves quality of life and may extend survival; in Australia, referral should be based on need rather than prognosis alone, per the Cancer Council Optimal Care Pathways.

For mild pain (Numerical Rating Scale 1 to 3), regular paracetamol 1 g four times daily is the foundation. Non-steroidal anti-inflammatory drugs provide additional benefit for bone pain and inflammatory components but require careful risk assessment given thrombocytopenia, renal impairment, and gastrointestinal risk in the cancer population.

For moderate pain (Numerical Rating Scale 4 to 6), a weak opioid such as codeine or low-dose immediate-release oxycodone or morphine is added. In Australian palliative practice, low-dose immediate-release opioids are generally preferred over weak opioids for their more predictable dose-response, aligning with the ACSQHC principle that immediate-release formulations should be used for titration and that modified-release formulations should not be introduced until background requirements are established.

For severe pain (Numerical Rating Scale 7 to 10), strong opioids are required. The eTG recommends oral morphine as the preferred first-line strong opioid in cancer pain. Dosing begins with immediate-release morphine every 4 hours with equivalent breakthrough doses (typically one-sixth of the total daily dose) available every hour as needed. Once the 24-hour opioid requirement is established over 24 to 48 hours of titration, conversion to a modified-release preparation is appropriate. Subcutaneous continuous infusion via a syringe driver is the preferred parenteral route in palliative care when the oral route is lost.

Neuropathic pain components require adjuvant agents added to the opioid backbone: gabapentin or pregabalin are first-line; low-dose tricyclic antidepressants (amitriptyline, nortriptyline) are an alternative where sedation is not a concern. Dexamethasone reduces peritumoural oedema and neuropathic pain from nerve compression. Bisphosphonates (zoledronic acid) or denosumab reduce skeletal-related events and pain from bone metastases and are initiated by the treating oncologist. Interventional approaches including nerve blocks, intrathecal drug delivery, and radiotherapy for bone pain are considered by the specialist multidisciplinary team.

6. Pharmacology and AU PBS notes

Morphine (immediate-release tablet or oral solution; modified-release tablet MS Contin, Kapanol) is the first-line strong opioid. It is PBS-listed for cancer pain; the PBS streamlined authority code for MS Contin and morphine oral solution in cancer is authority required (STREAMLINED) under Section 85. Oxycodone (immediate-release OxyNorm; modified-release OxyContin) is a valid alternative, particularly where morphine side-effects are limiting; also PBS-listed with authority. Hydromorphone (Jurnista modified-release; Dilaudid immediate-release) is used where oxycodone or morphine are not tolerated; PBS-listed. Fentanyl transdermal patches (Durogesic, generic fentanyl patches) are used for stable pain in patients unable to take oral medication but are not appropriate for dose titration given their 12 to 17-hour time to steady state; PBS-listed. Buprenorphine transdermal (Norspan) is suitable for patients with renal impairment. Methadone has a role in refractory cancer pain but requires specialist initiation due to complex pharmacokinetics and QTc prolongation risk. Adjuvants: gabapentin (Neurontin; PBS Section 85, non-authority for neuropathic pain), pregabalin (Lyrica; authority required), amitriptyline (non-PBS for neuropathic pain, paid out-of-pocket or private prescription), dexamethasone (PBS). All opioids should be co-prescribed with a stimulant laxative (e.g. senna plus docusate) from day one; an antiemetic (e.g. metoclopramide, haloperidol) for the first one to two weeks. Naloxone (Narcan) for opioid reversal should be available in all inpatient settings.

7. Complications and monitoring

Opioid-related adverse effects requiring active monitoring include constipation (nearly universal; managed with stimulant laxatives and adequate hydration), nausea and vomiting (typically self-limiting after one to two weeks; treat with metoclopramide or haloperidol), sedation and cognitive impairment (dose-dependent; review for opioid accumulation, renal function, drug interactions), respiratory depression (uncommon at therapeutic doses in opioid-tolerant patients; risk increases with rapid escalation, concurrent benzodiazepines, or renal failure), and opioid-induced hyperalgesia (paradoxical pain worsening with dose escalation; managed by opioid rotation). The ACSQHC standard mandates documentation of opioid adverse effect monitoring and access to naloxone in all settings where opioids are prescribed. Ongoing surveillance in cancer pain includes reassessment of pain intensity and functional impact at each clinical encounter, monitoring of renal and hepatic function at intervals guided by disease trajectory, review of opioid requirements after each anticancer treatment change, and advance care planning review to ensure goals of care remain aligned with analgesic strategy. Bone pain from metastases warrants imaging review if new or escalating to exclude pathological fracture or impending spinal cord compression. Hypercalcaemia of malignancy should be rechecked when pain escalates unexpectedly, as it can mimic or worsen pain perception.

Written for Australian practice and grounded in the guidance named above. Study material only — not medical advice. Always check against current guidelines.