5-Fluorouracil (5-FU) is an essential component of systemic chemotherapy for colorectal cancer (CRC) in the palliative and adjuvant settings. Over the past four decades, several modulation strategies including the implementation of 5-FU-based combination regimens and 5-FU pro-drugs have been developed and tested to increase the anti-tumor activity of 5-FU and to overcome the clinical resistance. Despite the encouraging progress in CRC therapy to date, the patients' response rates to therapy continue to remain low and the patients' benefit from 5-FU-based therapy is frequently compromised by the development of chemoresistance. Inter-individual differences in the treatment response in CRC patients may originate in the unique genetic and epigenetic make-up of each individual. The critical element in the current trend of personalized medicine is the proper comprehension of causes and mechanisms contributing to the low or lack of sensitivity of tumor tissue to 5-FU-based therapy. The identification and validation of predictive biomarkers for existing 5-FU-based and new targeted therapies for CRC treatment will likely improve patients' outcomes in the future. Herein we present a comprehensive review summarizing options of CRC treatment and the mechanisms of 5-FU action at the molecular level, including both anabolic and catabolic ways. The main part of this review comprises the currently known molecular mechanisms underlying the chemoresistance in CRC patients. We also focus on various 5-FU pro-drugs developed to increase the amount of circulating 5-FU and to limit toxicity. Finally, we propose future directions of personalized CRC therapy according to the latest published evidence.

During the past two decades the first sequencing of the human genome was performed showing its high degree of inter-individual differentiation, as a result of large international research projects (Human Genome Project, the 1000 Genomes Project International HapMap Project, and Programs for Genomic Applications NHLBI-PGA). This period was also a time of intensive development of molecular biology techniques and enormous knowledge growth in the biology of cancer. For clinical use in the treatment of patients with colorectal cancer (CRC), in addition to fluoropyrimidines, another two new cytostatic drugs were allowed: irinotecan and oxaliplatin. Intensive research into new treatment regimens and a new generation of drugs used in targeted therapy has also been conducted. The last 20 years was a time of numerous in vitro and in vivo studies on the molecular basis of drug resistance. One of the most important factors limiting the effectiveness of chemotherapy is the primary and secondary resistance of cancer cells. Understanding the genetic factors and mechanisms that contribute to the lack of or low sensitivity of tumour tissue to cytostatics is a key element in the currently developing trend of personalized medicine. Scientists hope to increase the percentage of positive treatment response in CRC patients due to practical applications of pharmacogenetics/pharmacogenomics. Over the past 20 years the clinical usability of different predictive markers has been tested among which only a few have been confirmed to have high application potential. This review is a synthetic presentation of drug resistance in the context of CRC patient chemotherapy. The multifactorial nature and volume of the issues involved do not allow the author to present a comprehensive study on this subject in one review.

Thymidine phosphorylase (TP), also known as "platelet-derived endothelial cell growth factor" (PD-ECGF), is an enzyme, which is upregulated in a wide variety of solid tumors including breast and colorectal cancers. TP promotes tumor growth and metastasis by preventing apoptosis and inducing angiogenesis. Elevated levels of TP are associated with tumor aggressiveness and poor prognosis. Therefore, TP inhibitors are synthesized in an attempt to prevent tumor angiogenesis and metastasis. TP is also indispensable for the activation of the extensively used 5-fluorouracil prodrug capecitabine, which is clinically used for the treatment of colon and breast cancer. Clinical trials that combine capecitabine with TP-inducing therapies (such as taxanes or radiotherapy) suggest that increasing TP expression is an adequate strategy to enhance the antitumoral efficacy of capecitabine. Thus, TP plays a dual role in cancer development and therapy: on the one hand, TP inhibitors can abrogate the tumorigenic and metastatic properties of TP; on the other, TP activity is necessary for the activation of several chemotherapeutic drugs. This duality illustrates the complexity of the role of TP in tumor progression and in the clinical response to fluoropyrimidine-based chemotherapy.

An economic analysis (based on interim data from a long-term, randomised, multi-centre, controlled, clinical trial) to evaluate chemotherapy with XELOX (capecitabine/oxaliplatin) versus FOLFOX6 (5Fluorouracil/leucovorin/oxaliplatin) as an adjuvant treatment for high risk colorectal cancer patients in Greece.

As survival rate was the same in the two arms, a cost-minimisation analysis was carried out, from the perspectives of the National Health Service (NHS), Social Insurance Funds (SIF) and patients in Greece. Patient data were combined with 2008 unit prices to estimate the total cost of patient care, the patients' travelling expenditure and their productivity losses. Raw data were bootstrapped 5000 times in order to allow statistical testing.

From an NHS perspective, the mean chemotherapy cost was 8762 euro with FOLFOX6 and 9713 euro with XELOX; costs of administration and hospitalisations were 5154 euro and 1050 euro, respectively. Total treatment cost with FOLFOX6 reached 17,480 euro and with XELOX 12 525 euro, a difference of 4955 euro (p < 0.001) in favour of the latter therapy. From an SIF perspective, the total cost of treatment was 16,240 euro with FOLFOX6 and 12,617 euro with XELOX, a reduction of 3623 euro (p < 0.001) with the latter therapy. Mean patient travelling cost was 184 euro with FOLFOX6 and 80 euro with XELOX, a difference of 104 euro (p < 0.001). Mean productivity loss was 100 euro with FOLFOX6 and 31 euro with XELOX, a difference of 69 euro (p < 0.001).

Chemotherapy combining oral capecitabine and oxaliplatin reduces total treatment cost for the Greek National Health Service and Social Insurance Funds, mainly through a reduction in the cost of administration. From patients' perspective, it reduces travelling expenditure and productivity losses. Therefore, this combination may be a cost-effective approach for the management of colorectal cancer patients who have had surgery in Greece. This is an analysis alongside a clinical trial, and should be interpreted in this specific context in which it was undertaken.

Capecitabine is currently the only novel, orally home-administered fluorouracil prodrug. It offers patients more freedom from hospital visits and less inconvenience and complications associated with infusion devices. The drug has been extensively studied in large clinical trials in many solid tumors, including breast cancer, colorectal cancer, gastric cancer, and many others. Furthermore, the drug compares favorably with fluorouracil in patients with such cancers, with a safe toxicity profile, consisting mainly of gastrointestinal and dermatologic adverse effects. Whereas gastrointestinal events and hand-foot syndrome occur often with capecitabine, the tolerability profile is comparatively favorable. Prompt recognition of severe adverse effects is the key to successful management of capecitabine. Ongoing and future clinical trials will continue to examine, and likely expand, the role of capecitabine as a single agent and/or in combination with other anticancer agents for the treatment of gastrointestinal as well as other solid tumors, both in the advanced palliative and adjuvant settings. The author summarizes the current data on the role of capecitabine in the management of gastrointestinal cancers.

Xeloda (capecitabine), a thymidine phosphorylase activated fluoropyrimidine carbamate, is currently the only universally approved orally administered 5-fluorouracil (5-FU) prodrug. It belongs to a newer generation of orally administered fluoropyrimidines. It has been developed because of the clinical need for efficient, tolerable and convenient agents, which do not require continuous infusion. Capecitabine is not a cytotoxic drug in itself, but via a three-step enzymatic cascade, it is converted to 5-FU mainly within human cancer cells. While the drug compares favorably with 5-FU in patients with advanced or metastatic colorectal cancer and pretreated breast cancer, it also has an improved toxicity profile, mainly of gastrointestinal and dermatologic effects with a significantly lower incidence of grade 3/4 myelotoxicity compared with infusional 5-FU-based chemotherapy. Capecitabine's selective activation within the tumor allows for less systemic toxicity events. A gradient of fluoropyrimidine toxicity is observed: high in the US and low in East Asia. In addition, there is a discrepancy in tolerance of dose among patients treated in the US vs. Europe. Although patients can take the drug orally in the convenience of their own home, the key to successful management of capecitabine is the clinician's awareness of its severe, but low in incidence, adverse effects, and the patients' education, emphasizing compliance with the treatment plan, prevention and timely recognition of its toxicities.

Capecitabine is a recently developed oral antineoplastic prodrug of 5-fluorouracil. It has demonstrated a favorable tolerability profile, with low incidence of myelosuppression. Vinorelbine, a third generation vinca alkaloid, works by inhibiting mitosis and interfering with cells' ability to synthesize DNA and RNA. The present study investigates the therapeutic value of single use capecitabine on solid tumour tissues in vitro using breast cancer cell lines and as reference. The data is to be compared with the use of vinorelbine which is a conventionally applied drug for advanced breast cancer patients.

The trucut biopsies of 35 metastatic breast tumour patients were obtained. The tissues were cultured for 24h. Capecitabine and vinorelbine were added according to the corresponding groups to be cultured by another 24h. Plain medium was added for control group. The two cell lines chosen were BT-783 and MB-MDA-231 to act as a reference group. The metabolic rate of the tissues and cell lines were measured by ATP bioluminescence assay and the proliferation rate was measured by WST-1. The level of COX2 and p16 after capecitabine and vinorelbine treatment was assessed with immunohistochemical methods.

One-way ANOVA revealed lower metabolic rate in test groups than control in cell lines and tumour tissues. WST-1 showed similar trend in both cell lines. COX2 and p16 staining showed decreases in cell size and number after drug use.

Capecitabine demonstrated similar inhibitory effects as vinorelbine in breast cancer cell lines and solid tumour tissues at decreasing cell proliferation and metabolism as well as decreasing the expression of metabolic proteins and tumor suppressor genes. Capecitabine also has the added benefits of convenient oral administration and lower cost.