Some studies have noted an association between CgA concentrations and tumor location or degree of differentiation. It has also been proposed that plasma CgA levels are more frequently elevated in well-differentiated tumors compared with poorly differentiated tumors of the midgut. Some other clinical series have provided evidence of an association between plasma CgA levels and the extent of disease, tumor burden, or presence of metastases, and high baseline levels of CgA are suggestive of a poor prognosis.