Pomalidomide either as single therapy or in combination with cyclophosphamide, elotuzumab, bortezomib, or daratumumab are effective treatment regimens in relapsed refractory multiple myeloma (RRMM). Standard dosing is 4 mg/day during 21 days of a 28-day cycle (21/28). However, a clear dose-response association for pomalidomide in patients with multiple myeloma (MM) is lacking. There is data supporting that a dose of 2 mg/day continuously (28/28) induces fewer side effects while efficacy is preserved, compared to 4 mg/day continuously. The response in patients who received pomalidomide 2 mg per day compared to 4 mg per day was higher, with a longer duration of response. In addition, a randomized phase II study showed no difference in efficacy between 4 mg (21/28) and 4 mg continuously. These clinical studies support that a dosage of pomalidomide of 2 mg (28/28) is at least comparable with a dosage of 4 mg (21/28). It is not known if 4 mg every other day (EOD) is comparable to a dosage of pomalidomide 2 mg (28/28) or 4 mg every day (QD, 21/28). For cost reasons, this is interesting as the costs of pomalidomide 4 mg and 2 mg are comparable. Therefore, from a patient and societal perspective, the investigators want to explore if an alternative scheme would be possible by performing a PKPD bio-equivalence pilot study.

Pomalidomide either as single therapy or in combination with cyclophosphamide, elotuzumab, bortezomib, or daratumumab are effective treatment regimens in relapsed refractory multiple myeloma (RRMM). Standard dosing is 4 mg/day during 21 days of a 28-day cycle (21/28). However, a clear dose-response association for pomalidomide in patients with multiple myeloma (MM) is lacking. There is data supporting that a dose of 2 mg/day continuously (28/28) induces fewer side effects while efficacy is preserved, compared to 4 mg/day continuously. The response in patients who received pomalidomide 2 mg per day compared to 4 mg per day was higher, with a longer duration of response. In addition, a randomized phase II study showed no difference in efficacy between 4 mg (21/28) and 4 mg continuously. These clinical studies support that a dosage of pomalidomide of 2 mg (28/28) is at least comparable with a dosage of 4 mg (21/28). It is not known if 4 mg every other day (EOD) is comparable to a dosage of pomalidomide 2 mg (28/28) or 4 mg every day (QD, 21/28). For cost reasons, this is interesting as the costs of pomalidomide 4 mg and 2 mg are comparable. Therefore, from a patient and societal perspective, the investigators want to explore if an alternative scheme would be possible by performing a PKPD bio-equivalence pilot study.

Inclusion Criteria:

• Patients with relapsed/refractory multiple myeloma, who are eligible for a treatment regimen which contains pomalidomide. Either monotherapy or in combination with bortezomib, daratumumab, cyclophosphamide, or elotuzumab
• Patients who received a minimum of two cycles of pomalidomide 4mg every day on day 1-21/28
• Age > 18 years
• WHO performance status 0-3
• Written informed consent

Exclusion Criteria:

• Usage of CYP1A2 inhibitors (e.g. ciprofloxacin, enoxacin, ketoconazole, carbamazepine, fluvoxamine, and grapefruit juice)
• Renal insufficiency requiring dialysis
• Significant hepatic dysfunction (total bilirubin > 330 μmol/l or transaminases > 3 times normal level)
• Current smoker
• Hemoglobin <6.5 mmol/L
• Thrombocytes <100 *10^9/L
• Neutrophiles <1.5 *10^9/L
• Pregnant patients
• Female patients who are able to get pregnant and who do not agree to adequate birth control or complete abstinence
• Male patients who do not agree to adequate birth control or complete abstinence
• Hypersensitivity to pomalidomide or constituents