• Background Multiple myeloma (MM) is a haematological malignancy characterised by uncontrolled plasma cell proliferation leading to bone damage, anaemia, kidney failure, and hypercalcemia. Venous thromboembolism (VTE) represents a significant concern in MM and more than 10% of patients develop a VTE. The currently most used thromboprophylaxis regimens consist of either aspirin or prophylactic low molecular weight heparin (LMWH). The choice between the two depends on patient risk assessment according to the International Myeloma Working Group (IMWG) guidelines. Due to the associated high VTE risk, MM patients have an inherent need for thromboprophylaxis which is an essential part of their care. The previous randomized controlled trials (RCTs) comparing aspirin with LMWH observed no major bleeding events and only one minor bleeding in the LMWH group and when comparing aspirin with LMWH and warfarin, major bleeding events were observed only in three patients (1.4%) who received aspirin. Moreover, six patients (2.7%) in the aspirin group, one patient (0.5%) in the warfarin group, and three patients (1.4%) in the LMWH group experienced minor bleeding events. However, clinically relevant non-major bleedings (CRNMBs) were not reported, and the follow-up varied widely between the two studies. The risk-benefit ratio between the different regimens is yet unclear and it is difficult to conclude which anticoagulation should be implemented as standard of care in daily practice. Moreover, the current regimens, namely LMWH, might be perceived as burdensome by MM patients due to their subcutaneous administration. Therefore, it is unclear whether thromboprophylaxis represents an additional significant burden for MM patients because of the method of administration or adverse bleeding events.
• Main research question What is the current real-life bleeding incidence in MM patients receiving thromboprophylaxis and what is the perceived burden of thromboprophylaxis?
• Design (including population, confounders/outcomes) This prospective observational study will include newly diagnosed MM patients receiving thromboprophylaxis. The International Society on Thrombosis and Haemostasis (ISTH) bleeding criteria and the ISTH bleeding assessment tool (ISTH-BAT) will be adapted to the daybook format, patient friendly vocabulary and translated to Dutch. Patients will be asked to record bleeding events for 6 months after starting thromboprophylaxis. Incidence of bleeding events stratified per major, minor and CRNMB will be calculated with death as competing risk. Bleeding events in LMWH and aspirin patients will be compared with a double-sided z test for independent proportions. Quality of life will be assessed with validated questionnaires. Lastly incidence of VTE and arterial thrombosis (AT) will be calculated.
• Expected results In an RCT comparing LMWH with aspirin prophylaxis for a fracture of an extremity, bleeding events occurred in 14% of patients receiving aspirin and 14% of patients receiving LMWH within 90 days of follow-up. Since comparable doses will be used in this study, we expect to see similar results.

Inclusion Criteria:

• Patients must be newly diagnosed with MM.
• MM patients must be receiving thromboprophylaxis (aspirin or LMWH).
• Patient must be willing or able to fill-in questionnaires.

Exclusion Criteria:

• Patients objecting to the use of their data for research purposes.

Newly diagnosed multiple myeloma patients with an indication for thromboprophylaxis.