The effect of tumor bulk on the metabolic response to cancer.

The derangements in energy/substrate metabolism seen in oncology patients are similar regardless of the tumor's site of origin, and in advanced disease these metabolic derangements can be manifested as cancer cachexia. The relationship between tumor size and the degree of metabolic abnormality, however, remains unclear. Using primed constant infusions of stable and radiolabeled isotopes and indirect calorimetry, the authors have determined the rates of net protein catabolism (NPC), glucose oxidation, Cori cycling of glucose, and oxygen consumption in 85 patients with cancer. They have assessed the association between bulk of tumor and metabolic abnormality using regression analysis. A positive correlation was found between tumor bulk and the rates of NPC (r2 = 0.8), plasma glucose appearance (r2 = 0.72), plasma glucose clearance (r2 = 0.70), the percentage of tissue glucose uptake recycled to lactate (r2 = 0.62), and oxygen consumption (r2 = 0.79). The percentage of tissue glucose uptake oxidized was negatively correlated with tumor bulk (r2 = 0.75). The data indicate that the degree of metabolic abnormality seen in cancer patients is closely related to the quantity of malignant tissue present. Progressive increase in tumor size is associated with an increase in peripheral substrate mobilization, an increase in the rate of hepatic glucose production, an increase in tissue glucose uptake, an increase in energy-expensive glucose cycling to lactate, and an increase in protein loss.