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In this issue of HealthNews, Dr Kok Jaan Yang, Senior Consultant, Palliative Medicine, answers some common questions about cancer pain.

What causes cancer pain?

Cancer pain is generally caused by cancer invading and damaging the surrounding tissues or organs of the body. However, not all pain experienced by advanced cancer patients is directly caused by cancer. An estimated 5–10 percent of pain in cancer patients is reported to be due to cancer treatment (e.g. mouth ulcer pain after certain chemotherapy) and up to 20 percent of the pain may be unrelated to their cancers (e.g. osteoarthritis of the knee).

Do all cancer patients suffer severe cancer pain?

It is a widely-held belief that all cancer patients will suffer from severe cancer pain. But this is not true. Up to 25 percent of advanced cancer patients may not experience any pain issues at all in their cancer journey, approximately 50 percent may have mild to moderate cancer pain, and only 25 percent may have severe cancer pain, of which 5 percent would have very severe cancer pain.

How is cancer pain managed?

The medical oncologist managing your treatment will assess the cause(s) of the cancer pain. If the cause is due to tumour mass, and it can be shrunk by radiation, chemotherapy, or other anti-cancer treatment, the cancer pain can be reduced.

Meanwhile, some pain relieving medications may be prescribed to relieve the pain. These include paracetamol, non-steroidal anti-inflammatory drugs (e.g. diclofenac, naproxen, etoricoxib or celecoxib) and weak opioids (e.g. tramadol).

In cases of severe cancer pain, strong opioids such as morphine, oxycodone or fentanyl may be used to control their pain.

Cancer patients experiencing neuropathic or nerve pain may also be prescribed other additional drugs such as pregabalin or gabapentin.

Can regular intake of morphine or other strong opioids for cancer pain lead to addiction?

The act (or need) of taking morphine or other strong opioids to control pain is not an addiction. In Singapore, patients who are taking morphine or strong opioids under the careful supervision of their experienced doctors have not shown to lead to any addiction problem.

When the cancer pain can be reduced by other means (e.g. radiation therapy for cancer bone pain), the dosage of morphine or strong opioids can be reduced significantly or even stopped.

Should I worry about the side effects of morphine or other strong opioids?

Morphine or other strong opioids can cause three common side effects: drowsiness, nausea/vomiting and constipation. Fortunately, these side effects can be managed relatively easily.

Drowsiness is usually experienced when a patient is first started on the medication or when the dosage is increased. It typically improves after a few days. Persistent or severe drowsiness can be mitigated by reducing the dosage or stopping the medication.

Nausea and vomiting affects only one in three users. They can be countered with anti-vomiting drugs such as metoclopramide, domperidone or ondansetron. In the long-term, they typically go away after patients get accustomed to the medication.

Opioid-induced constipation is a common side effect. It can be easily managed by drinking sufficient fluids and taking common laxatives such as senokot or lactulose.

The medical oncologist managing your treatment is the best person to manage your cancer pain. They may also refer you to a palliative medicine specialist to help co-manage your cancer pain. Together, they can help develop a pain management plan that involves educating you and your caregiver(s) on pain coping mechanisms, and devising a combination of different classes of pain relieving medicines for better control of cancer pain with minimal side effects.