Protein synthesis dynamics in human gastrointestinal malignancies

The malnourishing effects of cancer and its treatments have provided a strong clinical incentive for the nutritional support of cancer patients with intravenous hyperalimentation (IVH), but potential enhancement of tumor growth by additional substrate provision has generated concern. Twenty-five patients undergoing surgical treatment for gastrointestinal cancer were studied on one of two preoperative dietary regimens: ad libitum oral diet or intravenous hyperalimentation. Using a stable isotope tracer, ¹⁵N-glycine, in vivo tissue fractional protein synthesis rates were determined from operative specimens of tumor and normal gastrointestinal tissue. Despite substantial advantage in caloric and protein intake, and nitrogen retention, tumors in IVH-fed patients were synthesizing protein no faster (14.2%/day) than those in orally fed patients (15.1%/day). Tumor fractional protein synthesis rates (PSRs) correlated (r = + 0.708, P < 0.005) with the PSR of the tissues from which they arose. IVH maintained gut PSR at the level occurring in the orally fed patients. Parenteral nutritional support in cancer patients does not maintain protein synthesis rates at levels greater than those present with regular oral diets. Although not a direct measure of tumor growth, these data provide preliminary evidence that optimal nutritional support of the cancer patient may be possible without undesirable stimulation of tumor growth.