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Children with hemato-oncological diseases may have significant skeletal morbidities. Vitamin D is essential for the maintenance of skeletal health and may also be important for immunological functions and cancer outcomes. As vitamin D deficiency is a recognized problem in children worldwide, it is important to evaluate its prevalence among children and adolescents with hemato-oncological diseases in Sweden.

In this thesis, I investigated vitamin D status and its predictors, serum hCAP-18 (the pro-protein of the antimicrobial peptide LL-37 produced during neutrophil differentiation in the bone marrow), and bone turnover markers in children with hemato-oncological diseases at the time of diagnosis. 

Vitamin D deficiency was found in 30.9–46% of the children. Lower 25-hydroxyvitamin D level correlated with older age, seasons outside summer, a more recent calendar year of sampling, lack of vitamin D supplementation, and country of parental origin located between latitudes -45° and 45°. In preschool children with leukemia, a 25-hydroxyvitamin D level < 50 nmol/L was associated with inferior overall survival. 

There was no correlation between serum 25-hydroxyvitamin D and hCAP-18 neither in children with hemato-oncological diseases nor in healthy controls. Children with diseases that impair myelopoiesis presented low hCAP-18 levels, whereas those with non-hematological malignancies displayed serum hCAP-18 levels in the same range as that of healthy children.

Children diagnosed with leukemia had lower levels of bone formation and resorption markers than those of children with solid tumors or bone marrow failure. Adolescents with osteosarcoma displayed high bone alkaline phosphatase levels.

The identification of patients with suboptimal vitamin D status and compromised bone remodeling at cancer diagnosis may aid the development of supportive treatments that reduce the adverse effects of cancer and its treatment.