Alternative Medicine Review 2000 (Dec); 5 (6): 546–552 ~ FULL TEXT
Adam Hayashi, MS, Aric C. Gillen, MS, and James R. Lott, PhD
The benefits of fruits and vegetables have been studied fairly extensively. Flavonoids, found in many plants, are of particular interest for their anticancer properties. In his text, Boik divides the flavonoids into five categories: anthocyanins, minor flavonoids, flavones or flavonoids, isoflavonoids, and tannins.  Quercetin, a member of the flavones group, is thought to be the most widely distributed in nature; approximately 25-50 mg of quercetin is consumed in a normal daily diet.  Bioflavonoids have been reported to be involved in several important biological processes including antihistamine effects, immunological modulation, inhibition of platelet aggregation, and antitumor activity.
Early research conducted on the effect of oral administration of quercetin on colon-25 tumors in balb-c mice showed a significant reduction (50%) in size.  This research was based on reported antitumor properties of quercetin including: lymphocyte proliferation,  neutrophilia,  free radical scavenging,  anti-angiogenesis,  down-regulation of the mitotic cycle in tumor cells,  gene expression alteration,  and induction of apoptosis (cell suicide).  A comprehensive review of quercetin's antitumor effects was conducted recently by Lamson and Brignall and published in this journal. 
An important remaining question is how much quercetin is absorbed from an oral dose. Varying estimates have been concluded from clinical studies, ranging from less than one percent to 50 percent (this in ileostomy patients). [12-15]
The purpose of this study was to examine the effects of modified citrus pectin and quercetin chalcone on colon-25 tumors implanted in balb-c mice. The parameters measured were tumor size (length x width) and tumor weight (grams). The changes in mean weight of tumors from mice treated with either MCP or QC were not statistically significant.
The significant decrease in mean tumor size noted in mice fed citrus pectin might be attributable to MCP's effect on metastasis. In their work with MCP, Platt and Raz found MCP not only reduced the number of experimental metastases, but also reduced the volume of developed metastases.  In a related article, Raz points out the importance of tumor emboli (tumor fragments) not only in tumor dissemination, but also in formation of tumors at secondary sites.19 It seems, according to Pienta, that MCP may inhibit the formation of organized tumor emboli.  MCP, because of its small size and galactose-rich side chains, may be able to bind to cell surface galectins (galactose-binding lectins) on tumor cells, preventing the cells from binding to host cell surfaces. This could explain the reduction in tumor size seen with MCP (Figure 2). The tumor brei, a collection of cells extracted from the medulla of a colon tumor, once implanted in the mouse may not be able to undergo adequate implantation and growth due to the presence of MCP. Indeed, when looking at Figure 2 , an early departure in growth rates between the experimental and control groups can be seen.
The significance seen in the 1.6-mg/mL QC group may indicate anticancer mechanisms similar to quercetin. Due to its similar structure, similar effects might be expected. Quercetin has been shown to: (1) down-regulate the expression of the mutant p53 gene in breast cancer cell lines; (2) cause G1 phase arrest in several cancer cell lines; (3) inhibit tyrosine kinase responsible for tumor growth; and (4) bind to estrogen II receptor sites, reducing expression of ER negative cells.  More research needs to be conducted before such correlations can be made between quercetin and quercetin chalcone. The early results, however, look promising.
Future research might focus on earlier administration of these substances. In the present study, QC and MCP dosing began on day eight, predictably the first day of manual tumor palpation. It is not known what effect might occur if these substances were given on the day of tumor implantation or before. We can infer from these results that tumor growth should be significantly inhibited, but the extent of that inhibition cannot be accurately predicted from the present data. Further animal and human clinical research utilizing these promising substances is suggested.