Cancer Pain — Causes, WHO Analgesic Ladder, Opioids & Palliative Care Guide — Symptoms, Causes & Treatment | MyMedicPlus

Cancer pain is one of the most feared and prevalent symptoms in oncology — and also one of the most undertreated. It affects approximately 55% of patients during active cancer treatment and 66% of those with advanced or metastatic disease. Despite effective treatments being available, studies show that 43% of patients with cancer pain receive inadequate analgesia. Pain in cancer is multidimensional — encompassing physical, psychological, social, and spiritual suffering (Cicely Saunders' concept of 'total pain'). It may arise directly from the tumour, from cancer treatments (surgery, radiotherapy, chemotherapy-induced peripheral neuropathy), or from concurrent conditions. The WHO three-step analgesic ladder (1986, revised) provides a globally applicable framework for titrating analgesia from non-opioids through mild opioids to strong opioids according to pain severity, transforming cancer pain management worldwide.

Cancer pain has three principal mechanisms: Nociceptive somatic pain: direct tumour invasion of bones, soft tissues, or skin — described as aching, gnawing, or throbbing; well-localised; responds well to opioids. Bone metastases are the most common cause of somatic cancer pain (breast, prostate, lung, kidney, and thyroid cancers most frequently metastasise to bone). Nociceptive visceral pain: tumour involvement of internal organs — described as deep, cramping, pressure-like; may be poorly localised or referred (liver capsule pain referred to right shoulder; pancreatic pain referred to the back). Responds to opioids; adjuvant treatment may include steroids. Neuropathic pain: damage to peripheral or central nervous system — described as burning, shooting, stabbing, or electric shock-like; often accompanied by allodynia (pain from non-painful stimuli) or hyperalgesia; caused by nerve compression, infiltration, chemotherapy-induced peripheral neuropathy (CIPN — vincristine, taxanes, platinum agents), radiation fibrosis, or post-surgical nerve injury. Responds partially to opioids; requires adjuvant neuropathic agents. Mixed pain: most cancer pain involves components of more than one mechanism.

Comprehensive pain assessment is essential before treatment selection. Characteristics to assess (SOCRATES mnemonic): Site (location and radiation), Onset (sudden/gradual, relationship to position, movement), Character (aching, burning, stabbing, shooting, pressure), Radiation (to other areas), Associated features (nausea, autonomic symptoms), Time/pattern (constant vs. intermittent, diurnal variation), Exacerbating and relieving factors (movement, eating, position), Severity (numerical rating scale 0–10, or verbal descriptor scale). Breakthrough pain (BTP): episodic severe pain flares on a background of otherwise controlled pain — affects up to 70% of cancer patients with pain; may be: incident (predictable — e.g., on movement, dressing changes) or spontaneous (unpredictable). BTP requires a separate 'rescue dose' prescription. Pain intensity tools: numerical rating scale (NRS 0–10); verbal rating scale (none/mild/moderate/severe); visual analogue scale (VAS); ABBEY Pain Scale for cognitively impaired patients. Associated symptoms: sleep disturbance, depression, anxiety, reduced physical function — all bidirectionally linked to pain severity and requiring parallel management.

Pain diagnosis in cancer requires identifying the underlying cause of pain (tumour progression, treatment-related, intercurrent pathology) to guide targeted treatment. Imaging: CT/PET-CT — assesses tumour extent, bone involvement, organ invasion; bone scan (technetium-99m scintigraphy) — sensitive for bone metastases; MRI — detailed soft tissue and nerve involvement, spinal cord compression assessment. Spinal cord compression assessment: urgent MRI spine required in any cancer patient with back pain plus neurological symptoms (leg weakness, sensory loss, bladder or bowel dysfunction) — this is a palliative oncological emergency requiring IV dexamethasone 16 mg immediately and radiotherapy or surgical decompression within 24 hours. CIPN assessment: CTCAE (Common Terminology Criteria for Adverse Events) neuropathy grading; nerve conduction studies in complex cases. Bone fracture risk: DEXA scan; FRAX score — relevant in cancer patients on long-term corticosteroids or androgen deprivation therapy. Blood tests: FBC (anaemia contributing to fatigue and pain perception); CRP, ESR (inflammatory component); calcium (hypercalcaemia of malignancy — causes bone pain, confusion, constipation, nausea).

WHO Analgesic Ladder principles: analgesics should be given by mouth (oral preferred), by the clock (regularly scheduled — not on demand), by the ladder (step-wise dose escalation), and tailored to the individual. Step 1 — mild pain: paracetamol 1 g QDS; ibuprofen 400 mg TDS or diclofenac 50 mg TDS (NSAIDs — effective particularly for bone pain and inflammatory pain, but use with caution in renal impairment, platelet dysfunction, and peptic ulcer disease); add PPI gastroprotection. Step 2 — moderate pain: codeine 30–60 mg QDS (prodrug of morphine — 10% of patients are poor metabolisers); tramadol 50–100 mg QDS (weak mu-opioid + SNRI — useful in neuropathic pain). Step 3 — severe pain: strong opioids are the mainstay. Morphine sulphate (oral): start 5–10 mg four-hourly (immediate release) titrating by 30–50% every 24–48 hours to achieve pain control; convert to modified release (morphine SR, e.g., MST Continus) once stable dose established; breakthrough dose = 1/6th of total daily dose as immediate release. Alternative strong opioids: oxycodone (more predictable bioavailability than morphine); hydromorphone; transdermal fentanyl patch (72-hourly — useful for stable pain in patients with swallowing difficulties, avoiding peak-trough fluctuation); subcutaneous opioid infusion via syringe driver for end-of-life care. Opioid rotation: if unacceptable side effects or poor analgesia, switch to an alternative opioid using equianalgesic conversion tables. Adjuvant analgesics by pain type: Bone pain — bisphosphonates (zoledronic acid 4 mg IV monthly; denosumab 120 mg monthly SC — reduces skeletal-related events); radiotherapy (single fraction 8 Gy or 20 Gy in 5 fractions) for bone metastases; NSAIDs; corticosteroids (dexamethasone 4–8 mg daily). Neuropathic pain — gabapentin 300–3600 mg/day in 3 divided doses; pregabalin 75–600 mg/day BD; amitriptyline 10–75 mg nocte; duloxetine 60–120 mg daily (particularly CIPN). Interventional procedures: coeliac plexus block (pancreatic and upper GI pain — 70–80% effective); intrathecal drug delivery; vertebroplasty/kyphoplasty (vertebral metastases); TENS. Radiotherapy and oncological treatments for pain: palliative radiotherapy is highly effective for bone metastases (60–70% achieve significant pain relief); chemotherapy, hormone therapy, or immunotherapy treating the underlying tumour also reduces tumour-related pain.

Inadequately controlled cancer pain causes severe suffering and wide-ranging physical, psychological, and social consequences. Uncontrolled pain accelerates functional decline — patients with poorly managed pain experience reduced mobility, inability to eat or sleep, progressive deconditioning, and dependency on caregivers. Psychological complications: uncontrolled cancer pain is the single greatest driver of cancer-related depression and anxiety — approximately 30–40% of cancer patients develop clinically significant depression, and untreated pain dramatically worsens the severity and persistence of psychological distress. Deconditioning and cancer cachexia: pain-related immobility accelerates sarcopaenia, cardiorespiratory deconditioning, and the catabolic effects of cancer cachexia. Pathological fractures: bone metastases causing severe pain are at risk of fracture through normal loading — pathological fractures of the femur or spine cause immediate loss of mobility or neurological injury; prophylactic surgical fixation or radiotherapy is required when fracture risk assessment (Mirels score) indicates high risk. Opioid side effects require proactive management: opioid-induced constipation (affecting 40–90% of patients on strong opioids) can lead to obstruction; opioid-induced nausea and sedation impair quality of life; in high doses or renal failure, opioid neurotoxicity causes myoclonus, delirium, and respiratory depression. Spinal cord compression, if not diagnosed and treated urgently, leads to permanent paraplegia — making timely recognition of back pain with new neurological symptoms critical in any cancer patient with bone involvement. Hypercalcaemia of malignancy causes bone pain, confusion, nausea, and constipation and can be life-threatening if untreated without IV bisphosphonates and hydration.

Proactive pain management prevents escalation to uncontrolled pain — all cancer patients should have regular pain assessments at every clinical encounter. Prescribe analgesics regularly and by the clock, not on a PRN (as required) only basis — this prevents pain from returning to severity before the next dose. Always co-prescribe a laxative with opioids (macrogol or senna — opioid-induced constipation affects 40–90% of patients); anti-emetic for the first week of opioid initiation (metoclopramide or haloperidol); and consider proton pump inhibitor with NSAIDs. Preventing CIPN where possible: dose reduction or drug substitution in patients developing grade 2+ CIPN; duloxetine is the only medication with established evidence for established CIPN. Patient and carer education: written information on correct opioid use, recognising undertreated pain, and safe storage and disposal of opioids. Multi-disciplinary pain team involvement: palliative care physician, pain nurse specialist, clinical psychologist, physiotherapist, occupational therapist — the 'total pain' model recognises and addresses psychosocial and existential suffering alongside physical pain.

Patients with cancer should report new, worsening, or uncontrolled pain to their oncology team or GP promptly — undertreated cancer pain is never acceptable and effective treatments are available. Seek emergency assessment immediately for: new-onset severe back pain with leg weakness, numbness, or bladder/bowel symptoms (spinal cord compression — call emergency services); sudden severe chest pain or breathlessness in a cancer patient (pulmonary embolism, pleural effusion); pathological fracture (sudden inability to bear weight in a patient with known bone metastases). Contact your specialist palliative care team, palliative care nurse, or oncology team urgently for: pain rated above 7/10 on a 0–10 scale despite current medications; severe breakthrough pain episodes (more than 3 per day); unmanageable opioid side effects (severe sedation, confusion, persistent vomiting); or any rapid change in the pattern or character of existing pain — this may indicate new disease progression.