Endocrine/metabolic syndromes of cancer.

In addition to producing symptoms directly by their mass or invasion of tissues, cancers may also make themselves evident by the secretion of cytokines, protein hormones, or hormone precursors, which in turn, results in recognizable clinical syndromes. This article reviews the endocrine syndromes of cancer, their pathophysiologic basis, and the means of diagnosis. Many of these protein hormones appear to be produced in small amounts by normal tissues where they act in paracrine fashion as cytokines. Furthermore, neoplastic transformation is associated with continued, or often dramatically amplified, production of paracrine substances, permitting them to circulate in the blood and to act as hormones. Thus, classical definitions of cytokines and hormones become blurred. In this context, so-called "ectopic" cancer production is not ectopic, but rather a modification of normal cell function. The majority of the endocrine syndromes of cancer are caused by cancer production of these cytokines or hormones. Except for cancers originating in the adrenals or gonads, cancers do not synthesize steroids and secrete them, although very rarely a cancer may metabolize a normal steroid precursor to produce a biologically active steroid.