The myeloma microenvironment is the target of many drugs in development, and it is unclear how they can be combined with reference treatments such as lenalidomide. This pilot study consists of an extensive phenotypic characterisation of the impact of lenalidomide combined with dexamethasone on the bone marrow microenvironment of a homogeneous cohort of non-pretreated MM patients. Blood sampling will be systematically performed in a matched fashion to monitor the general effect of lenalidomide on the immune system and to detect possible peripheral markers.

This study will provide rational guidance for future combination therapies with lenalidomide.

With the significant increase in the number of therapeutic combinations targeting the tumour microenvironment, it is crucial to better understand the effect of reference myeloma treatments on the different immune populations present in the tumour in order to rationally optimise the combination with new strategies under development. In addition, the identification of biomarkers in the circulating blood that can predict/monitor the impact of new therapies on the immune response is a major challenge.

This pilot study consists of an extensive phenotypic characterisation of the impact of lenalidomide combined with dexamethasone on the bone marrow microenvironment of a homogeneous cohort of non-pretreated MM patients. Blood sampling will be systematically performed in a matched fashion to monitor the general effect of lenalidomide on the immune system and to detect possible peripheral markers.

Inclusion Criteria:

• Patient with newly diagnosed multiple myeloma;
• Patient not eligible for intensive treatment;
• Patient for whom first-line treatment with Lenalidomide-Dexamethasone will be initiated;
• Patient accepting the performance of an additional myelogram at the end of the 1st treatment cycle.
• Patient aged 18 years or older;
• Patient who has given free, informed and written consent;
• Patient affiliated to a social security scheme
• For women of childbearing age, use of effective contraception

Exclusion Criteria:

• Patient with relapsed multiple myeloma;
• Patient eligible for intensive treatment;
• Patient for whom chemotherapy involves treatment other than Lenalidomide-Dexamethasone;
• Patient with a contraindication to lenalidomide treatment
• Pregnant or breastfeeding woman;
• Person subject to legal protection (safeguard of justice, curatorship,guardianship) or person deprived of liberty.