Pain is a common symptom in palliative care cancer patients and is often insufficiently relieved. The 2010 INCA report showed that France is not an exception to this worldwide observation (synopsis of the 2010 national survey). This report shows that pain is the symptom that these patients fear the most and that it dramatically impacts their quality of life. These patients may experience nociceptive pain related to stimulation of sensory nerve endings by the tumour. When tumour resection is impossible, a symptomatic analgesic treatment is generally proposed, mainly consisting of administration of opioid analgesics. At high doses, this treatment induces adverse effects, especially drowsiness and psychomotor retardation that impair the patient's quality of life.

They may also experience neuropathic pain, secondary to anatomical lesions or functional impairment of nerve structures (peripheral nerves or cerebral or spinal tracts) related to repeated surgical procedures and/or radiotherapy. This type of pain may respond to antiepileptic or antidepressant drugs. At high doses, these treatments also induce adverse effects fairly similar to those observed during treatment of nociceptive pain. As these two types of treatment often need to be coprescribed, these patients frequently present an almost permanent state of drowsiness at the end of life, preventing all normal activities of daily living.

In recent years, noninvasive brain stimulation (NIBS) techniques (transcranial magnetic stimulation (rTMS) or transcranial direct-current stimulation (tDCS)) have been successfully used to treat chronic pain. It was shown that these NIBS techniques can improve pain in cancer patients in the palliative care setting.

tDCS appears to be more suitable than rTMS for the treatment of palliative care patients, who are often difficult to mobilize, as tDCS can be delivered at the patient's bedside and possibly even at home, which is not the case with rTMS. tDCS also appears to be rapidly effective (after 5 sessions) in the context of cancer pain, and this effect lasts longer than that of rTMS.

The proposed treatment of refractory cancer pain by tDCS in palliative care patients is a new treatment modality that is well adapted to hospitalised patients. Each patient will receive 20 minutes of transcranial direct-current stimulation daily for 5 consecutive days.

One arm will receive active stimulation and the control arm will receive sham stimulation. Patients and investigators will be blinded to the type of tDCS.

By improving the patient's activities of daily living, this treatment will enable the patient to return home under good conditions for both the patient and the caregivers. This treatment can also be continued at home. This strategy is consistent with current guidelines in this field, in which the priorities are improvement of quality of life, return home and decreased workload for caregivers.

Inclusion criteria

1. Patient with a confirmed cancer at a palliative stage
2. Pain whose mean intensity is greater than or equal to 4/10 in the 48 hours preceding inclusion
3. Pain present on a daily or almost daily basis (at least 4 days out of 7)
4. Pain that has been present for at least 48 hours before inclusion
5. Patients aged 18 or over
6. Patients who can be followed for the duration of the study (i.e. 3 weeks)
7. Patients affiliated to a health insurance plan or entitled
8. Life expectancy estimated at more than 3 weeks
9. Agreeing to participate in the study and having signed an informed consent

Exclusion criteria

1. Inability to self-assess pain and complete self-questionnaires
2. History of head trauma or neurosurgical injury
3. Symptomatic intracranial hypertension (HTIC)
4. Uncontrolled epilepsy
5. Impossibility to correctly positioning the medical device
6. Abuse of drugs or psychoactive substances, at the discretion of the investigator
7. Current major depression or psychosis
8. Pregnant or breastfeeding woman
9. Patient already included in a research protocol on pain
10. Patient under legal protection
11. Absence of affiliation to a social security scheme
12. Specific contraindication to tDCS (intracerebral metal implant)
13. Patients deprived of liberty
14. Patients undergoing psychiatric care.