SPP1 and neoplasm: Some of these factors are the general condition of the patient, tumor size, nodal load, age, the existence of comorbidities, previous treatments administered and TNM classification, along with other elements identified in blood samples (inflammatory markers, such as interleukins and C-reactive protein; indirect markers of hypoxia, such as osteopontin, carbonic anhydrase IX and lactate dehydrogenase; or indirect markers of tumor burden, such as carcinoembryonic antigen or cytokeratin 21-1 fragments) [135,136,137,138,139,140,141,142,143,144].