Bone metastases from neuroendocrine tumors: clinical and biological considerations

We considered 351 patients affected by neuroendocrine tumors, followed at the University Hospital of Padua and at the Veneto Oncological Institute. Of these, 72 (20.5%) suffered from bone metastases. The sample was divided according to the timing of presentation of bone metastases into synchronous (within 6 months of diagnosis of primary tumor) and metachronous (after 6 months). We collected data on the type and grading of the primary tumor, and on the features of bone metastases. Our analysis shows that the group of synchronous metastases generally presents primary tumors with a higher degree of malignancy rather than the ones of the metachronous group. This is supported by the finding of a Ki-67 level in GEP-NETs, at the diagnosis of bone metastases, significantly higher in the synchronous group. Moreover, in low-grade NETs, Chromogranin A values are higher in the patients with synchronous metastases, indicating a more burden of disease. The parameters of phospho-calcium metabolism are within the normal range, and we do not find significant differences between the groups. Serious bone complications are not frequent and are not correlated with the site of origin of the primary tumor. From the analysis of the survival curves of the total sample, a cumulative survival rate of 33% at 10 years emerges. The average survival is 80 months, higher than what reported in the literature, while the median is 84 months. In our observation period, synchronous patients tend to have a worse prognosis than metachronous ones with 52-months survival rates of 58% and 86%.