Multiple myeloma (MM) patients that develop bortezomib and lenalidomide-resistant disease have a very poor survival of only a median of 9 months. This clearly illustrates that new anti-MM agents are needed with different mechanisms of action.~Importantly, daratumumab monotherapy is effective and well tolerated in heavily pre-treated lenalidomide and bortezomib-refractory myeloma patients. However, approximately 60% of patients do not achieve a partial response, and ultimately all patients, also those achieving complete response, will develop progressive disease during daratumumab therapy. Factors that determine the susceptibility of MM cells to daratumumab include levels of the target antigen CD38, and expression levels of the complement inhibitory proteins CD55 and CD59. At the time of progression, there is a reduced level of CD38 on the MM cells, whereas CD55 and CD59 levels are increased. This indicates that these factors are also involved in the development of daratumumab-resistant disease.~Importantly, ATRA upregulates CD38 levels and downregulates CD55/CD59 levels on MM cells, both in daratumumab naïve cells and in cells that are resistant to daratumumab because of previous exposure to this drug. These alterations in expression explain the strong synergy between ATRA and daratumumab, both in MM cells derived from daratumumab naïve patients and from patients with daratumumab-refractory disease.~These data form the preclinical rationale for clinical evaluation of ATRA and daratumumab in MM patients. The investigators will treat relapsed/refractory MM patients in two stages. The first stage (part A) consists of treatment with daratumumab monotherapy. In case these patients have progressive disease after cycle 1, less than minimal response after cycle 2, or less than partial response after cycle 3 (unless ongoing response) to single agent daratumumab, or in case these patients progress during daratumumab therapy after previous response, then ATRA will be added to daratumumab (part B).~The aims of this study are to develop a safe ATRA and daratumumab combination suitable for clinical use and evaluation in subsequent randomized clinical trials. To this end, the maximum tolerated dose (MTD) of ATRA and daratumumab will be determined for patients with relapsed/refractory disease, who were treated with daratumumab but failed to achieve a partial response, or developed progressive disease during daratumumab treatment. This will be followed by a second part in which the investigators will examine the effectivity and toxicity profile of the combination at the MTD.
Multiple myeloma (MM) patients who develop bortezomib and lenalidomide-resistant disease have a very poor survival of only a median of 9 months, indicating that new agents are urgently needed. Recent studies have shown that daratumumab as a single agent is effective and well tolerated in these heavily pretreated MM patients. However, approximately 60% of patients do not achieve a partial response, and ultimately all patients will develop progressive disease during daratumumab therapy.~The investigators have demonstrated that levels of the target antigen CD38, and expression levels of the complement inhibitory proteins CD55 and CD59 determine the susceptibility of the MM cells towards daratumumab. In addition, MM cells have lower CD38 expression levels and higher levels of CD55/CD59 at the time of progression. Importantly, all-trans retinoic acid (ATRA) upregulates CD38 levels and downregulates CD55/CD59 levels on MM cells, both in daratumumab naïve cells and in cells that are resistant to daratumumab because of previous exposure to this drug. These alterations in expression explain the strong synergy between ATRA and daratumumab, both in MM cells derived from daratumumab naïve patients and from patients with daratumumab-refractory disease.~These data form the preclinical rationale for clinical evaluation of ATRA and daratumumab in MM patients.