The aim of the study is to evaluate the prevalence of positive anti BP180 and/or anti BP230 serology in the serum of patients with chronic and diffuse pruritus for at least 1 month under immunotherapy and in the absence of obvious pruritic dermatosis (e.g. scabies, contact eczema...).

Inclusion Criteria:

• Patient currently receiving immunotherapy (pembrolizumab, nivolumab, atezolizumab, durvalumab) as monotherapy or in combination OR patient who has received immunotherapy (pembrolizumab, nivolumab, atezolizumab, durvalumab) as monotherapy or in combination within the last 6 months.
• Patients with chronic (> 1 month) diffuse pruritus, which started after the start of immunotherapy and in the absence of an obvious pruritic dermatosis.
• Woman of childbearing age with effective contraception (see GTFG) (estrogen-progestin or intrauterine device or tubal ligation) for 1 month (negative urine/blood pregnancy test) or Postmenopausal woman: confirmatory diagnosis (non-medically induced amenorrhea for at least 12 months prior to the inclusion visit)
• Major patient
• Patient having read and understood the information letter and signed the consent form
• Patient affiliated to a social security scheme

Exclusion Criteria:

Pruritus prior to immunotherapy. Bullous pemphigoid prior to immunotherapy End-stage chronic renal failure (GFR < 15ml/min or dialysis) Clinical jaundice or total bilirubin > 34 µmol/L Hepatic cholestasis Diabetes mellitus complicated by diabetic neuropathy. History of polycythemia vera History of Hodgkin's lymphoma iron deficiency anemia Current treatment including DPP-4 inhibitors (vildagliptin, linagliptin) Treatment with systemic corticosteroids or immunosuppressant for more than one month.

Pregnant or parturient or breastfeeding woman or absence of proven contraception

· Person deprived of liberty by an administrative or judicial decision or person placed under legal safeguard / sub-tutorship or curatorship