Ozone Therapy in Chemotherapy-induced Peripheral Neuropathy: RCT (O3NPIQ)

Inclusion Criteria: * 1\. Adults \> = 18 years old. * 2\. Any kind of cancer in any stage, treated with any kind of chemotherapy, and life expectancy \> = 6 months. * 3\. Clinical diagnosis of painful chemotherapy-induced peripheral neuropathy, toxicity Grade 2 or higher according to the Common Toxicity Criteria for Adverse Events (CTCAE) from the National Cancer Institute of EEUU, v.5.0, for \> = 3 months and without the inclusion of new treatments for pain and/or neuropathy for \> = 1 month. * 4\. "Average pain" \> = 3/10 according to the Brief Pain Inventory-Short Form (BPI-SF) \> = 3 months beyond chemotherapy completion. * 5\. Pregnant women cannot participate in the clinical trial. * 6\. Before enrollment, women of childbearing potential should obtain a negative result in the serum or urine pregnancy test at the screening visit and accept the use of appropriate contraceptive methods at least from the 14 days prior to the first ozone therapy session up to 14 days after the last one. * 7\. Patients who have signed and dated the study 's specific informed consent Exclusion Criteria: * 1\. Age \< 18 years old. * 2\. Pregnancy at the time of enrollment. * 3\. Women with childbearing potential who are unwilling to perform a pregnancy test and/or employ adequate contraception from the 14 days prior to the first ozone therapy session up to 14 days after the last one. * 4\. Clinical suspicion that peripheral neuropathy (compressive or diabetic neuropathy) in the same area prior to receiving neurotoxic chemotherapy. * 5\. Psychiatric illness or social situations that would limit compliance with study requirements. * 6\. Those who are unable to fill in the scales used to measure quality of life variables * 7\. Specific liver enzymes \[Aspartate Aminotransferase (AST), and Alanine Aminotransferase (ALT) \> 5 times the upper limit of normal * 8\. Increased creatinine \> 3 times the upper limit of normal. * 9\. Hemodynamically or clinically unstable patients or uncontrolled severe illness. * 10\. Uncontrolled cancer disease. * 11\. Leptomeningeal carcinomatosis. * 12\. Life expectancy \< 6 months * 13\. Contraindication or disability for rectal ozone administration or to attend scheduled treatments. * 14\. Known allergy to ozone. * 15.Patients who do not meet all the inclusion criteria.