Prospective Multicentre Study of the Use of Ketamine in the Treatment of Refractory Chronic Pain in the French CLCC

Almost 382,000 new cancers have been diagnosed in France in 2018. Regular progresses in their management have improved the overall survival of patients, sometimes with sequelae that may be particularly painful. Thus for 20 to 45% of patients treated for breast cancer, pain persists 5 years later.

If remission is a regularly reached target, cancer was also the cause of 157,000 deaths in 2018 in France, preceded by months or years of progression of a chronic disease that regularly causes pain. Pain during cancer (chronic cancer pain for CIM-11) remains a frequent symptom, and its prevalence has slightly changed during the last 20 years.

In the European EPIC study, carried out in 2006, 76% of the cancer patients (and 62% of French patients) presented moderate to severe pains linked to cancer, daily for more than half of them.

Even when identified, chronic cancer pain is still under-treated in 25 to 60% of cases worldwide, including in the most developed countries.

When well-managed, pain's management now allows the relief of almost 80% of patients. Pain's management is based in particular on a precise and adapted use of the different opioids through different routes of administration (oral, transdermal, trans-mucosal, parenteral, etc.).

A neuropathic component of pain exists in almost a third of cases and may require specific treatments when opioids are insufficient. In all cases, the treatment is integrated into a multidisciplinary management, in connection with the ongoing oncological treatments, the loco-regional treatments available (radiotherapy, interventional radiology, etc.) and with an adapted psychosocial management.

Ketamine is an NMDA receptor antagonist (N-Methyl-D-Aspartate) indicated as a high dose anesthetic. It is used in the context of peri-operative pain for its anti-hyperalgesic properties. These properties have led to its use also in palliative care (outside the marketing authorization [AMM]) to treat hyperalgesia linked to the use of high-doses of opioids, as well as depression. For non-cancer pains, ketamine is widely used by centres and consultations specialized in refractory chronic pain management in different pains not relieved by standard treatments: neuropathic pain, fibromyalgia, etc., or even in opioids weaning aid.

The bibliographic data are not homogeneous and of low quality. Despite the weakness of the available data, ketamine is widely used in France in chronic pain in situation of therapeutic impasse. The protocols used vary according to the prescribers and services practices: venous route in general, sometimes subcutaneous or even oral; doses varying from 30 to 200 mg / day, infusion duration varying from a few hours to several days, discontinuous administration by cycle or continuous administration, etc.

Current knowledge is too limited in oncology to have a consensus on the use of ketamine :

- Often retrospective studies with heterogeneous treatment protocols;

- Studied populations also heterogeneous, with insufficiently documented indications;

- Staff not able to answer adequately the questions raised. This situation largely explains the heterogeneity of the Ketamine practices of use in oncology

It is essential to draw up an inventory of the ketamine use by the French CLCCs pain teams and to identify the profile of patients in whom i) the treatment is ineffective and must be avoided regarding toxicities ii) the potential efficacy required further investigations. Built on a methodology close to the OKAPI study, the KETACANCER study will enable to compare indirectly the results of the two studies.

To do this, it is proposed to conduct the KETACANCER prospective study in a precise population defined a priori, and corresponding to the following indications:

- Neuropathic sequelae pain

- Additional effect of morphine

- Morphine weaning.