Evaluation of a selective screening for colorectal carcinoma: the Taiwan Multicenter Cancer Screening (TAMCAS) project.

BACKGROUND: Although the efficacy of mass screening for colorectal carcinoma (CRC) with a fecal occult blood test has been demonstrated in several randomized trials, a mass screening approach used in countries with intermediate or low incidence of CRC might be costly. Screening high risk people may be an alternative approach, to aid in the prevention of death from CRC. However, the efficacy of CRC screening for high risk people in such countries is uncertain. METHODS: For this study, a multicenter design was devised to identify high risk groups without clinical symptoms related to CRC; these subjects were identified through the study of index cases of CRC in Taiwan. Colonoscopy, in combination with a fecal occult blood test or double-contrast barium enema, was used to screen high risk groups. A total of 8909 subjects were invited to attend screening. Of 8909, 81 with asymptomatic CRC were detected in one-shot screening. Markov models, in conjunction with a simulated approach, were proposed to estimate relevant parameters in relation to disease progression and to assess the effect of the interval between screenings on the efficacy of CRC screening for these high risk groups. RESULTS: The estimated preclinical incidence rate was 0. 00396 (95% confidence interval [CI], 0.002944-0.004985), which was 21 times that reported from a cancer registry in 1994. The simultaneous estimations of mean sojourn time (the average duration between the preclinical screen-detectable phase and the clinical phase) and sensitivity were 2.8 years (95% CI, 2.15-4.30) and 95.0% (95% CI, 24.4-99.9%), respectively. Predictions of mortality reduction for people who received annual, biennial, and triennial screening regimes compared with controls were 26% (95% CI, 0-50%), 23% (95% CI, 0-48%), and 21% (95% CI, 0-47%), respectively. CONCLUSIONS: The efficacy of selective colorectal carcinoma screening has been demonstrated in this study. A high preclinical CRC incidence rate also suggests that such a screening strategy might be cost-effective for countries with intermediate or low incidence of CRC. Methods proposed in this study can be used to evaluate the efficacy of CRC screening in similar screening trials.

Megadose of vitamin C delays insulin response to a glucose challenge in normoglycemic adults.

The effect of a megadose of ascorbic acid (AA) on glucose and insulin responses after an oral-glucose-tolerance test (OGTT) is unknown. With a double-blind, placebo-controlled design, nine normoglycemic subjects (22 +/- 1 y, mean +/- SEM) consumed AA (2 g/d) or placebo for 2 wk after a 2-wk washout period with placebo, and an OGTT was performed after an overnight fast. This 4-wk protocol was repeated in a crossover fashion. Plasma glucose was significantly elevated 1-h postprandial in vitamin C-saturated subjects vs those taking a placebo. The plasma insulin response curve was shifted rightward in vitamin C-saturated subjects relative to baseline: plasma insulin was significantly depressed at 0.5 h postprandial but significantly elevated at 2 h postprandial. These data indicate that elevated plasma AA delays the insulin response to a glucose challenge in normoglycemic adults, thereby prolonging the postprandial hyperglycemia. These effects might be partially explained by the competitive inhibition of glucose transfer into pancreatic beta cells by high concentrations of circulating AA.