¿what is the cancer pain?

Pain is a very common symptom in cancer patients, appearing in up to 90% of patients with a terminal disease. This type of pain is a complex and important problem in clinical practice, which requires a multidimensional treatment.

Causes of cancer pain

The causes are varied, and usually in a patient with cancer there are multiple causes and locations of pain.

The main causes of pain are:

• The tumor invasion of adjacent structures (70%): As may be the invasion of bony structures, invasion of vascular or nerve elements, intestinal obstruction or infiltration of hollow viscera.
• Diagnostic and therapeutic procedures (20%): among those include surgery, the side effects of chemotherapy (gastrointestinal and oropharyngeal mucositis, neurotoxicity) and / or radiotherapy (radiation enteritis, cystitis, osteonecrosis).
• Syndrome Induced neoplastic (<10%): As is Para neoplastic syndromes.
• Others reasons: osteoarthritis, osteoporosis, coronary heart disease, myocardial infarction.

Classification of cancer pain

Classically, the pain has been classified into three subtypes, based on the neurophysiology and neuroanatomy of pain:

1. Somatic Pain

   This occurs as a consequence of activation of nociceptors in the skin or deeper tissues. This is usually a well-localized pain. Some examples appear in patients with bone metastases, or in cases of musculoskeletal and myofascial pain.

2. Visceral-pain

   This type of pain arises after invasion or infiltration of thoracic, abdominal or pelvic viscera. Typically appears in peritoneal carcinomatosis, especially within the pancreatic cancer. It is a diffuse and poorly localized pain.

3. Neuropathic-pain

   Neuropathic pain is caused by a lesion or dysfunction in the central or peripheral nerves with. This type of pain is usually described as paroxysmal discharges with stinging or burning sensation, or as pricking or numbness and tingling.

   Another way of classifying the cancer pain is according to duration in time:

1. Acute-pain

   Acute-pain: is pain of short duration (less than 6 months duration), and usually of sudden onset. Occurs mainly after surgery.

2. Chronic-pain

   Chronic-pain: The pain usually comes on slowly, and usually lasts the more than 6 months.

Treatment of cancer pain

The treatment of cancer pain includes different aspects of pain, such as causes, triggers and relieving factors, mood and psychosocial dimension of the patient, the type of pain, and pain intensity.
The analgesic treatment of cancer pain depends upon the type of pain and intensity.
The recommended route of administration is the oral route, although the transdermal route(TD) is used frequently, particularly in patients with swallowing difficulties. The parenteral or subcutaneous route is used in cased of hospitalization or when the patient has a port-a-cath.

1. The first step Analgesia developed by WHO (World Health Organization) consists of acetaminophen (Paracetamol) and nonsteroidal antiinflammatory drugs (NSAIDs), and its use is only indicated in cases of mild to moderate cancer pain. This first step as the other two can be associated with the adjuvant drugs. Moreover, the first step can be combined with the second or third step. Acetaminophen in cancer patients should be used at a dose of 1 g / 8 hours orally (PO). The NSAID group consists of a large number of drugs; including ibuprofen in doses of 600 mg / 8 hours, especially in the treatment of bone metastases. The combination of two or more NSAIDs together is not recommended, but it is possible associate acetaminophen with an NSAID.
2. The second step Consists of minor opioids, among which include codeine and tramadol. However, it is noteworthy that the analgesic effect of codeine is weak, and as such use is not recommended, because in addition to its poor analgesic efficacy is very frequently associated with constipation. The drug of choice in this step is the tramadol that can be used at doses of 75-400 mg / day divided into 3 or 4 doses orally.
   Buprenorphine via transdermal patch, despite being classified as a major opioid should be included in this second step by low analgesic efficacy in severe cancer pain.
3. The third step In the presence of very severe pain (VAS> 6) that is not relieved with the previous drugs (NSAIDs, Tramadol, Buprenorphine) the opioid that should be used is morphine, which can be prescribed in forms of rapid and sustained release orally or through a nasogastric tube. Other major opioids frequently used in our environment are the transdermal fentanyl patches (sustained release) also administered by oral transmucosal or intranasal route (quick release), methadone, oxycodone, hydromorphone and tapentadol.
   This drugs have an analgesic ceiling, and the limiting dose is determined by the appearance of serious side effects such as depression of breathing, excessive sedation, nausea and vomiting, severe constipation or opioid neurotoxicity syndrome induced.
   Besides the aforementioned opioids must take into account the concomitant use of adjuvant drugs that sometimes are essential in the management of cancer pain, as in the case of neuropathic pain or bone metastases.
   The adjuvant drugs that can be used in the treatment of cancer pain include:

• Antidepressants: amitriptyline, paroxetine, fluoxetine, venlaflaxine.
• Anticonvulsants: carbamazepine, gabapentin, pregabalin, topiramate.
• Corticosteroids
• Benzodiazepines

We should mention that there are many other methods to achieve relief of cancer pain such as the use of bisphosphonates (zoledronate, alendronate, risedronate, pamidronate) in the treatment of bone metastases from breast or prostate cancer; situations which are also useful as radiopharmaceuticals using Samarium-153 and Strontium-90.

Palliative radiotherapy is very effective analgesic for bone metastases or soft tissue masses causing spinal cord compression.

Other methods that can be used in patients with severe pain that is resistant to the previous analgesic drugs are neuroablative techniques, such as neurolysis of the celiac plexus (in pancreatic cancer patients) with alcohol or phenol or placement of intrathecal /epidural catheters.