Vitamin D Status and Gastroenteropancreatic Neuroendocrine Neoplasms: Biological Rationale, Clinical Associations and...

Vitamin D deficiency is common in patients with gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs). Whether vitamin D status influences tumor aggressiveness and clinical outcomes remains uncertain. This review examines current evidence on the prevalence, determinants, clinical associations, and clinical relevance of vitamin D deficiency in GEP-NENs.

A narrative and critical review of the literature was conducted using the PubMed/MEDLINE, Scopus, and Web of Science databases. Clinical studies, observational cohorts, translational research, selected mechanistic studies, and current clinical guidelines addressing vitamin D metabolism and neuroendocrine neoplasms were evaluated.

Vitamin D deficiency has been reported in approximately 60-80% of patients with GEP-NENs. Low serum 25-hydroxyvitamin D concentrations likely reflect multiple disease-related factors, including malabsorption, pancreatic exocrine insufficiency, chronic diarrhea, previous gastrointestinal surgery, and nutritional impairment. Several observational studies have linked lower vitamin D status with markers of more aggressive disease, including higher Ki-67 proliferation index values and shorter progression-free survival. Nevertheless, the available data are heterogeneous, predominantly observational, and do not support a causal relationship between vitamin D deficiency and tumor progression. At present, the main clinical rationale for assessing vitamin D status is to support metabolic care, preserve bone health, and prevent osteoporosis.

Vitamin D deficiency is a frequent and clinically relevant comorbidity in patients with GEP-NENs. Although lower vitamin D status has been associated with markers of more aggressive disease, current findings do not support vitamin D supplementation as an anticancer treatment strategy. Prospective clinical and translational studies are needed to clarify the biological and clinical significance of vitamin D signaling in GEP-NENs.