Serratus Plane Block (SPB) Versus Capsaïcine Versus Botox-A for Chronic Neuropathic Pain in Post-mastectomy Syndrome

SerCaBot is a randomized, open-label, phase II clinical trial designed to evaluate the efficacy of a treatment with Serratus Plane Block (SPB) or Botox-A compared to capsaicin for the control of chronic neuropathic pain of post-mastectomy syndrom, that is not adequately managed by systemic treatment alone. 123 patients with will be recruited over 24 months at the Centre Oscar Lambret. This clinical trial will be proposed to patients with chronic neuropathic pain of post-mastectomy syndrome that is not adequately managed by systemic treatment alone. After consent, an inclusion assessment will be carried out including clinical examination, anamnesis, pain assessment (questionnaires PCS, NPS, DN4, NPSI and collect of antalgic treatment) and evaluation of quality of life (questionnaire SF12) and depression (questionnaire HADS). Patients will then be randomly assigned to one of three treatment groups : Capsaicin, Botox-A, SPB (41 patients per group). The randomization will be balanced 1:1:1, controlled by minimisation (with a random factor set at 0.8) for the distribution of the following factors: * Pain level at enrolment (continuous NPS) * Axillary dissection (yes vs. no) * Loco-regional adjuvant radiotherapy (yes vs. no) * Prior change of systemic treatment (yes vs. no) The study treatment will be administered 1 to 2 weeks after randomization. Treatment will be stopped prematurely in the event of unacceptable toxicity or complication. In each group, a repeat of the treatment may be considered after 12 weeks if further pain control is required. In the SPB group, a repeat is also possible every 2 weeks. Patients will be followed for 24 weeks after the study treatment. Follow-up will include: * 2 medical visits at 8 weeks and at 24 weeks including pain assessment (questionnaires NPS, NPSI, record of antalgic treatment), record of adverse events related to study treatment and assessment of quality of life (SF12 questionnaire) and depression (questionnaire HADS). * remote assessment at week-1, week-2, week-4 and week-6 including assessment of pain (questionnaires NPS, NPSI, record of antalgic treatment) and record of adverse events. This remote assessment will be repeated in case of repetition of treatment at week 12. Patients will withdraw from the study after the 24 week medical visit. Early withdrawal will be possible in case of patient's decision of withdrawal, breast surgery during follow-up, or death.