While the current data indicate that the Golgi is the main site of sialylation by ST6Gal I in most cells, the fact that soluble forms of ST6Gal I are detected in body fluids and media from cultured cells has raised questions concerning the functions of this extracellular ST6Gal I. It is known that ST6Gal I is not the only transferase that exists in a soluble form; other glycosyltransferases are also detected in the systemic circulation of cancer patients, where they are associated with disease severity and poor prognosis. The gene discussed is ST6GAL1; the disease is cancer.