The mechanism of pain is thought to be involvement of the vagus or phrenic nerve. Paraneoplastic processes may present with peripheral neuropathies, particularly in patients with lung cancer and lymphoma. Neuropathies are commonly reported in patients with malignancy (1.7%–5.5%) because of the direct effects of the tumor, paraneoplastic syndromes, and treatment-related toxicities.
Orofacial Pain due to Cancer Management
The most common acute oral side effect of radiation therapy and/or cancer chemotherapy is oral mucositis. Oral mucositis and associated pain are the most distressing symptoms reported by patients receiving head and neck radiation therapy and aggressive neutropenia-inducing chemotherapy regimens. Combined chemotherapy and radiation therapy results in increased frequency, severity, and duration of mucositis. (Refer to the section on Oral Mucositis in this summary for more information.)
Mucositis pain may interfere with daily activities in approximately one-third of patients, interfering with social activities and mood in more than half. Mucosal pain may persist long after the mucositis resolves. Reports of mucosal sensitivity at 1-year follow-up are common, suggesting that chronic symptoms may be related to tissue change, including epithelial atrophy and/or neuropathy.
Orofacial pain after HNC therapy can be caused by musculoskeletal syndromes, including temporomandibular disorders associated with muscular fibrosis, scar formation, and discontinuity of the jaw. Ablative surgery may lead to tissue defects that may cause significant loss of orofacial function. Resection of the maxilla and mandible leads to sensory impairment, and more than half of patients experience regional hyperalgesia or allodynia. Pain scores after surgery for HNCs are highest for oral cavity cancers, followed by cancers of the larynx and oropharynx.
At more than 6 months postsurgery, impairment due to moderate to severe pain may be seen in approximately one-third of patients. Analgesics and physiotherapy are commonly used in pain management in these patients. Long-term HNC survivors (>3 years) continue to suffer from more pain and functional problems. Surgery-related pain involves inflammatory and neuropathic pain mechanisms.
Postradiation osteonecrosis and bisphosphonate-associated osteonecrosis are recognized oral complications that may cause pain; clinical presentation may include pain, swelling, and bone exposure. Oral GVHD represents a local manifestation of a systemic disease post-HCT that may result in mucosal and arthritic pain. Viral reactivation of herpes viruses may cause pain. Postherpetic neuralgia may result in chronic pain causing painful dysesthesias in the affected area that may persist for years.
Treatment of Pain in Cancer Patients
Pain management should be directed at the diagnoses of etiologic factors, pain mechanisms involved, and pain severity. (Refer to the PDQ summary on Pain for more information.) Pain mechanisms in cancer include the following:
- Malignant disease.
- Complications of treatment.
- Tumor invasion, pressure on structures, or ulceration of mucosal surface.
- Nociceptive pain.
- Neuropathic pain.