Tumors of mesenchymal and epithelial origin produce IGF-2, which activates pathways in the tumors. In a minority of patients, the tumors (hepatomas, fibromas, and fibrosarcomas are the most common among many) release into the circulation enough IGF-2-related peptides to mimic the fasting hypoglycemia characteristic of patients with insulin-producing islet-cell tumors. Rarely, markedly elevated IGF-2 levels produce somatic changes suggestive of acromegaly. Typically, the elevated IGF-2 levels are associated with suppressed plasma levels of insulin, IGF-1, and GH. Complicating the pathophysiology are the IGF binding proteins (IGFBPs) that can bind IGF-2 and IGF-1, modifying hormone metabolism and action. IGFBP concentrations are often altered in the presence of these tumors. At the cellular level, the 3 hormone-related ligands, IGF-2, IGF-1, and insulin, all bind to 4 (or more) types of IGF-1 receptor (IGF-1R) and insulin receptor (IR). Each receptor has its own characteristic affinity for each ligand, a tyrosine kinase, and overlapping profiles of action in the target cells. The IGF-2R, in addition to binding mannose-6-phosphate-containing proteins, provides an IGF-2 degradation pathway. Recent evidence suggests IGF-2R involvement also in signal transduction. Surgery, the treatment of choice, can produce a cure. For patients not cured by surgery, multiple therapies exist, for the tumor and for hypoglycemia. Potential future therapeutic approaches are sketched. From 1910 to 1930, hypoglycemia, insulin, insulinomas, and non-islet-cell tumors were recognized. The latter third of the century witnessed the emergence of the immunoassay for insulin; the IGFs, their binding proteins, and assays to measure them; and receptors for the insulin-related peptides as well as the intracellular pathways beyond the receptor. In closing, we replace non-islet-cell tumor hypoglycemia, an outdated and misleading label, with IGF-2-oma, self-explanatory and consistent with names of other hormone-secreting tumors.

In the symposium entitled "Transcriptional controls of energy sensing," the authors presented recent advances on 1) AMP kinase, an intracellular energy sensor; 2) PGC-1α (peroxisome proliferator-activated receptor γ co-activator 1α), a transcriptional co-activator that has powerful effects on mitochondria; 3) methylation and demethylation in response to metabolic fluctuations; and 4) FGF21 (fibroblast growth factor 21) as an emerging hormone-like intercellular metabolic coordinator. This introduction places these advances within a broad overview of energy sensing and energy balance, with a focus on human evolution and disease. Four key elements of human biology are analyzed: 1) elevated body temperature; 2) complex prolonged reproductive pathways; 3) emergence of 4 large, well-defined fat depots, each with its own functional role; and 4) an immune system that is often up-regulated by nutrition-related signals, independent of the actual presence of a pathogen. We propose that an overactive immune system, including the "metabolic syndrome," was adopted evolutionarily in the distant past to help hold out against unconquerable infections such as tuberculosis, malaria, and trypanosomiasis. This immune activation is advantageous in the absence of other disease management methods, especially under conditions in which life expectancy is short. The inflammation has become a major agent of pathology in wealthy populations in whom the pathogens are a minor threat and life expectancy is long. The "Conclusions" section sketches cautiously how understanding the molecules involved in energy sensing and energy balance may lead to specific therapies for obesity and diabetes and for their complications.