Bisgin et al. BMC Cancer 2012, 12:58 http://www.biomedcentral.com/1471-2407/12/58 through the lack of essential survival signals, or actively, through the ligand-induced trimerization of specific death receptors of the tumor necrosis factor (TNF) receptor family, such as Fas, the TNF receptor, or TRAIL (TNF-related apoptosis-inducing ligand) receptor [14]. TRAIL (APO-2 ligand) is a transmembrane (type II) glycoprotein that also belongs to the TNF superfamily. The extracellular domain of TRAIL is homologous to that of other family members and shows a homotrimeric subunit structure. Like TNF and Fas ligand (FASL), TRAIL also exists physiologically in a biologically active soluble homotrimeric form, serum-soluble TRAIL; sTRAIL [15]. Several recent studies have indicated that sTRAIL is involved in the pathophysiology of different disease states such as cancer, viral infections, autoim- mune diseases and inflammation, and defective apopto- sis due to its interaction with its ligand preventing signaling for apoptosis may contribute to these diseases [16-21]. Several studies have shown that both the membrane- bound TRAIL and sTRAIL can induce apoptosis in a wide variety of tumor types by activating death receptors [22-24]. sTRAIL is also used as a positive marker for apoptosis [25]. However, it has been observed that the cytotoxic effects of antiangiogenic agents are increased in clinical phase II and III studies when these agents are combined with TRAIL-related therapies [26-28]. Another study with human glioblastoma cells has indi- cated that TRAIL inhibits angiogenesis stimulated by VEGF expression [29]. However, recently used RECIST parameters (Response Evaluation Criteria for Solid Tumors; responders vs. non-responders) are not adequate to document the dif- ferences in treatment response [30]. Therefore, there is a need for a sensitive, specific and reliable serum marker to monitor the therapeutic response. The purpose of our study was to evaluate the possible use of sTRAIL as a marker for bevacizumab treatment efficacy at the cell apoptosis-linked step. Methods The amount of released sTRAIL and VEGF was mea- sured by ELISA in the serum of 16 metastatic colon cancer patients with liver metastases, who also received bevacizumab therapy, and 10 age- and sex-matched healthy control individuals who did not receive the treatment. Serum samples were obtained before bevaci- zumab-based chemotherapy regimens and 3 months after. Serum samples were kept between 2 and 8°C, cen- trifuged at 10,000 rpm for 10 min, and then frozen at -81°C until assayed. ELISA was done using the Diaclone sTRAIL ELISA kit (Gen-Probe, Besancon, France) according to the Page 2 of 5 manufacturer’s instructions. Statistical analyses were performed using SPSS for Windows version 13.0 (SPSS Inc., Chicago, IL, USA). Group comparisons were made using the independent samples t test. Progression-free survival (PFS) was defined as the period from the begin- ning of chemotherapy until documented progression or death from any cause. Overall survival (OS) was defined as the period from the first day of treatment until the date of last follow-up or death. Written informed consent relating to the Declaration of Helsinki was obtained from all patients. The study was approved by Akdeniz University Local Committee on Ethics. Results The baseline clinical characteristics of the patients are summarized in Table 1. The serum sTRAIL concentra- tions before therapy were similar to those of the con- trols (Figure 1). Serum sTRAIL levels in metastatic colorectal cancer (MCRC) patients before bevacizumab- based chemotherapy and healthy controls were 1.12 ± 0.04 ng/ml and 1.17 ± 0.08 ng/ml, respectively. After bevacizumab treatment, seven out of 16 patients’ post- treatment sTRAIL ratios were significantly increased as shown in Figure 2. Nine patients had progressive diseases, resulting in an overall response rate (56.2%). Median overall survival was 9.4 ± 0.9 months in non-responders. Interestingly, these nine patients were the same ones who showed no increase in sTRAIL levels after bevacizumab treatment. Therefore, we wanted to know whether there was any correlation between sTRAIL levels and overall survival rates. Our study demonstrated that elevated sTRAIL levels after bevacizumab treatment were significantly associated with increased median overall survival of up to 20.6 months (Table 2). Not surprisingly, the serum VEGF levels were decreased in all patients who received bevacizumab therapy (data not shown). Serum VEGF levels in MCRC patients before bevacizumab-based chemotherapy were 211 ± 189 ng/ml, and 3 months after treatment, they decreased to 117 ± 18.9 ng/ml, similar to healthy con- trols (119.5 ± 35.1 ng/ml). Table 1 Colon cancer patients versus healthy individuals. Healthy Controls (n = 10) Colon Ca patients (n = 16) Age Sex Male Female 51, 8 8 (%80) 2(%20) 55, 18 12(%75) 4(%25) Age and sex distribution of metastatic colon cancer patients (n = 16) and healthy control individuals (n = 10)