Gao et al. BMC Cancer 2011, 11:177 http://www.biomedcentral.com/1471-2407/11/177 pathway with three enzymatic steps and two intermedi- ary metabolites involved in. At the last enzymatic step, the metabolite 5’-deoxy-5-fluorouridine (5’-DFUR) is converted to 5-FU by Thymidine Phosphorylase (TP) which is more active in tumor tissues than in normal tissues [7]. So, the overexpression of TP in tumor tissues can increase the concentration of 5-FU and thus enhance the anticancer effect. Current evidences indi- cate that the expression level of TP may influence the clinical outcome of capecitabine in non-small cell lung cancer, gastrointestinal adenocarcinoma, breast cancer, head and neck cancer, and so on [8-11]. Two large phase III clinical trials showed that capecitabine could substitute 5-FU in clinical administration [12,13]. Also capecitabine combined with cisplatin or paclitaxel has been proved to be an effective combination regimen used in patients with advanced gastric cancer as first- line or second-line treatment [13-15]. Taxane including paclitaxel (PTX) and docetaxel, is another active antitumor agent for gastric cancer. Tax- ane binds to b-tubulin, which is one of the major com- ponents of microtubule, and exerts its growth-inhibitory effects through the stabilization of microtubule, resulting in the growth arrest of tumor cells at the G2/M phase [16]. Several mechanisms have been suggested as responsible for taxane resistance: ① The overexpression of MDR1 gene which encodes P-glycoprotein able to efflux taxanes and other cationic drugs, thereby hamper- ing drug retention [17]; ② Point mutation in tubulin has been identified to be responsible for taxane resis- tance [18,19]. ③ The selective overexpression of b-tubu- lin isotypes is another mechanism of resistance [20]. Up to now, at least seven distinct b-tubulin isotypes (classes I, II, III, IVa, IVb, V and VI) have been reported in human, with a complex distribution pattern in various tissues [20]. Some researches found the presence of class III b-tubulin (b-tubulin III, TUBB3) inhibited the assembly of b-tubulin subunits promoted by paclitaxel [21] and TUBB3 expressed in some paclitaxel-resistant cells [22]. Many preclinical studies have shown high expression levels of TUBB3 are associated with pacli- taxel resistance in human lung cancer [23], ovarian can- cer [22], prostate cancer [24] and breast cancer [25] cell lines. In studies of lung cancer, breast cancer and ovar- ian cancer, there are reverse relations between TUBB3 expression and paclitaxel efficacy or prognosis of patients [26-28]. Now that the target of paclitaxel is b-tubulin, and study had reported that there were rare mutations in b- tubulin for gastric cancer (no mutations were found in 50 tumor samples) [29], we considered that the overex- pression of TUBB3 was the most probable mechanism of paclitaxel resistance in gastric cancer. This study was designed to demonstrate the clinical implications of TP Page 2 of 8 and TUBB3 expressions in capecitabine plus paclitaxel chemotherapy for advanced gastric cancer patients, and to identify potential predictors for patients with gastric cancer treated with capecitabine plus paclitaxel. Methods Patients Eligibility All patients in this study were retrospectively collected as following criteria: patients had histologically con- firmed metastatic gastric adenocarcinoma and at least one measurable lesion according to the response evalua- tion criteria in solid tumors guidelines [30]; patients were treated by capecitabine plus paclitaxel or cisplatin in gastrointestinal department of Beijing Cancer Hospi- tal from July 2003 to December 2008, and had com- pleted at least two cycles of chemotherapy; no any chemotherapy except for neoadjuvant or adjuvant che- motherapy (adjuvant chemotherapy completed over 12 months) was done; all patients underwent endoscopic biopsy from primary stomach before chemotherapy. Treatment Regimens The first-line chemotherapy regimens with capecitabine plus paclitaxel or cisplatin were administered to patients as following: capecitabine (Roche Laboratories Inc., Nut- ley, NJ) was given orally at a dose of 1,250 mg/m2 twice daily from day1 (d1) to day14 (d14) of 3-weeks cycle; paclitaxel (Hainanhaiyao Co., Ltd., China) was given at a dose of 80 mg/m2 by a 180-min i.v. infusion on d1 and d8 of each cycle; cisplatin (Qilu Pharmaceutical CO., LTD., China) was given at a dose of 80 mg/m2 by a 240-min i.v. infusion on d1 of each cycle. Treatment was continued until disease progression or unacceptable toxicity, or patients/physicians’ decision. Response Evaluation Chemotherapeutic response was evaluated every two months by computed tomography (CT) according to the Response Evaluation Criteria in Solid Tumors (RECIST) criteria. Patients were categorized by com- plete response (CR), partial response (PR), stable disease (SD), and progressive disease (PD). CR and PR patients were defined as responders, SD and PD patients as non- responders. The progression-free survival (PFS) and overall survival (OS) were calculated from the first day of therapy to disease progression and death from any cause, respectively. Immunohistochemistry analysis for TP and TUBB3 All tumor samples were retrospectively collected from patients, and two step method of immunohistochemis- try (IHC) was used to detect TP and TUBB3 in tumor sections. Formalin-Fixed Paraffin-Embedded tissue sec- tions with 4 μm thick were deparaffinized in xylene