The aim of this study is to assess the efficacy of range of dermo-cosmetic products (hand/feet serum, nail strengthening solution nail strengthening solution, dissolving oil and gloves/slippers) based on natural products and designed for cancer patients)on bispecific Ac-induced skin and nail toxicity in MM patients treated with anti-CD3xGPRC5D bispecific antibodies.

The effects of supportive care products will be studied as a preventive measure in patients starting treatment with bispecific Ac and as a curative measure in patients undergoing treatment.

Patients will be able to apply the products directly at home according to the study schedule, and a skin and nail toxicity skin and nail toxicity will be performed each time the patient comes for administration of bispecific Ac. Follow-up will be for a total of 6 months (or less if progression occurs earlier), and patients will be asked to complete a quality-of-life questionnaire at protocol inclusion and after 1 month and 6 months of supportive care.

Inclusion Criteria:

1. MM patient.
2. Patient starting anti-GPRC5D bispecific Ac therapy OR patient undergoing anti-GPRC5D bispecific Ac therapy with NCI-NCTCAE V5.0 grade ≥2 skin and nail toxicity.
3. Patient with written consent.

Exclusion Criteria:

1. Patients treated or considering treatment with dermatological drugs (dermocorticoids) normally used for hand-foot syndrome OR dermo-cosmetic products (serum or reparative solutions) other than those tested.
2. Patients with atomic dermatitis (eczema)
3. Patients allergic to one or more components of the products tested.
4. Pregnant or breast-feeding women.
5. Patients who are minors or under legal protection (guardianship or safeguard of justice).
6. Patient not affiliated to a social security scheme.