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ead and neck after 7 to IO days of TPN. The ability of these cellular kinetic alterations to improve tumor response to cycle - specific chemotherapy has not been studied in clinical populations.

SUMMARY

     Thus, the effect of exogenous nutrients to stimulate tumor growth and alter cell cycle kinetics remains controversial. Numerous animal/tumor models clearly demonstrate that oral and parenteral nutrition can significantly stimulate tumor cell growth and metastasis. Although cellular kinetic studies in humans have shown alterations following TPN administration, ab3ective measures of tumor growth and tumor protein synthesis have not been altered by TPN. Certainly there are significant differences between animal tumors and human malignancies, which may influence the outcome of these studies. First, tumor-doubling time in animal tumors is rapid and ranges from 2 to 7 days. In contrast, the most rapid doubling time of human tumors is 30 days and typical malignancies may double in several months to years. Second, tumor burden may occupy as much as 60% to 70% of weight in animal models. In distinction, human models occupy only a small percentage of total body weight and generally do not compete for circulating nutrients at the expense of host tissues. Third, tumor immunogenecity is variable in animal models. Animal tumors exhibit a range of high to almost no antitumor immunity. In general, human tumors posses weak tumor specific transplantation antigens and elicit minimal antitumor immunity. Tumor immunogenicity may be an important influence of nutrients as nutrition support can significantly support host immune function with prolonged administration.
     Thus, the controversy of tumor stimulation by nutrition supports remains. Additional clinical investigations are warranted to determine if specific nutrients significantly stimulate primary tumor growth or tumor metastasis. If alteration of tumor cell cycle kinetics can be achieved in human’s nutritional modulation of tumor growth may be used to improve tumor response to chemotherapy in the future. Alternatively, if specific nutrients are found to inhibit tumor growth or metastasis, a selective advantage to host nutritional support may be possible. Further basic research and clinical studies need to be performed to determine whether tumor modulation or selective host nutrition can be achieved in the cancer patient in the future.

VOCABULARY
l. Metabolic alteration 代谢改变
2. caloric 能量的
3. protein-calorie deprivation 蛋白质热能缺乏
4. nutritional repletion 营养补充
5. heterogeneith 异种性，多相性，不均匀性
6. hormone-sensitive 对激素敏感的
7. nutrient administration 应用营养素
8. total parenteral nutrition 全胃肠外营养
9. hypertonic 高渗的
10. Thymidine 胸苷
11. glycine 甘氨酸
12. Strain 种，族
13. long-chain 长链
14. cellular kinetic 细胞动力学的
15. doubling time 倍增时间

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