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

Inclusion Criteria : 1. Women aged ≥ 18 years; 2. Unilateral breast cancer treated by total or partial mastectomy: * with sentinel lymph node technique (SLN) or axillary dissection; * with or without immediate reconstruction using a prosthesis; * associated or not with radiotherapy and/or chemotherapy; 3. Presenting moderate to severe chronic neuropathic pain, defined by: * Numerical Pain Scale (NPS) ≥ 3 and DN4 ≥ 4, * on a localised aera ((≤ 240 cm²), at the surgical site, in the axillary hollow, or on the inner side of the ipsilateral arm, * between 3 and 9 months after breast surgery, * with indication of additional locoregional treatment in complement to a systemic treatment of chronic neuropathic pain, as recommended by the SFETD - French Society for the Study and Treatment of Pain (tricyclic antidepressants or IRSNA or gabapentinoid PLUS lidocaine patch, at the appropriate dosage) and implemented for at least 4 weeks; 4. Patient affiliated with a health insurance plan; 5. Patient informed and having consented to participate in the trial. Exclusion Criteria : 1. Ipsilateral breast cancer recurrence, regardless of the first treatment; 2. History of breast or thoracic surgery prior to mastectomy with residual pain; 3. Painful polyneuropathy related to chemotherapy requiring treatment; 4. Ongoing or planned loco-regional adjuvant radiotherapy within the next 8 weeks; 5. Treatment area not suitable for potential botulinum toxin type A treatment; 6. Breast reconstruction using flap or lipomodelling; 7. Indication for breast reconstruction within the next 8 weeks; 8. Chronic pain of another etiology such as: * Neuropathic pain secondary to a neuroma (localized pain), * Radiodermatitis, * Phantom breast pain, * Lymphedema, * Complex regional pain syndrome, * Adhesive capsulitis, * Fibromyalgia; 9. Hypersensitivity or allergy to anesthetics, capsaicin, naropein, clonidine hydrochloride, an amide-type local anesthetic, botulinum toxin type A, or any excipient contained in the preparations; 10. Infection or inflammation at the injection site; 11. Therapeutic/effective anticoagulation; 12. Clinical signs or medical history leading to the diagnosis of: * Hemostasis disorder, * Local infection, * Severe renal insufficiency (creatinine clearance \< 30 mL/min), * Thrombocytopenia \< 50,000 platelets/mm3; 13. Generalized muscle activity disorders (e.g., myasthenia, Lambert-Eaton syndrome); 14. Heart rate lower than 60/minute; 15. Severe bradyarrhythmia due to sick sinus syndrome or second or third-degree atrioventricular block; 16. State of depression (HADS score ≥ 11); 17. Other contraindication to any of the study treatments; 18. Inability for the patient to follow the study schedule; 19. Inability for the patient or the healthcare team to perform the treatment within 2 weeks; 20. Pregnant or breastfeeding women, women who are able to conceive and who do not use a highly effective method of contraception during the trial and for at least 1 month after the end of treatment ; 21. Patient under guardianship or curatorship.