Prevalence, outcomes, and complications of vitamin D deficiency among patients with multiple myeloma: Nationwide burden of disease.

Multiple myeloma (MM), constituting 10% of hematological malignancies, poses significant morbidity and mortality, especially with skeletal involvement. Bisphosphonate use in MM may lead to severe hypocalcemia due to vitamin D deficiency (VDD), exacerbating bone-marrow plasma cell burden. We aimed to assess VDD prevalence and its impact on outcomes in MM patients.