36.4% and stage III, 20%. The survival length distribu- tion between any two stages was significantly different (p < 0.05) by the log-rank test. These data demonstrated that TNM stage is a good predictor of ESCC outcome. SNPs in reference to GenBank accession AC_000021 were detected in 88 sites of the 982-bp mitochondria D-Loop region from blood samples [see Additional file 1], The sequence chromatograms show a clear single peak at each nucleotide position, indicating that mitochondria in ESCC individuals were homoplasmic. At first, we com- pared the distribution of germline SNPs at each site between ESCC and control patients to identify any link between an SNP and cancer risk; no association with ESCC cancer risk was detected in any SNP in the D-loop at p < 0.05 levels. We assessed the relationships between these SNPs and post-operational survival of these ESCC patients. The relationship between mtDNA genotype and survi- val was compared subsequently, the ESCC patients were divided into two groups on the basis of their genotype at each SNP site, the post-operational survival curve was plotted using the Kaplan-Meier method for all ESCC patients at these sites. A dramatic difference in survival rate appeared at 16274, 16278 (refers to rs41458645 in NCBI SNP database, http://www.ncbi.nlm.nih.gov/snp/) and 16399 alleles by the log-rank test (Figure 1). The 3 SNPs were previously identified in mitochondria data- base (http://www.mitomap.org). The frequent allele 16274G, and the rare alleles 16278T and 16399G were associated with a shorter period of survival, with p = 0.0431, 0.0064 and 0.0028, respectively (Figure 1A, B and 1C). We performed multivariate analysis with Cox proportional hazards model including the factors of three SNPs and TNM stage. We coded G as 0 and A as 1 at 16274 position, C as 0 and T as 1 at 16278, A as 0 and G as 1 at 16399. We also coded I of TNM stage as 0, II as 1 and III as 2. As shown in Table 2, the 16278 and 16399 alleles were identified as independent predic- tors for ESCC outcome. The length of survival for patients with the rare allele 16278T genotype was signif- icantly shorter than that for patients with the frequent allele 16278C (relative risk, 3.001; 95% CI, 1.029 - 8.756; p = 0.044) at the 16278 site. The same was seen for the rare allele 16399G genotype when compared with matched alleles 16399A at the 16399 site in ESCC patients (relative risk, 3.483; 95% CI, 1.068 - 11.359; p = 0.039) (Table 2). These data demonstrated the strong prediction power of 16278C/T and 16399A/G on out- come for ESCC patients. Figure 1 Survival curve according to the nucleotide at position (A) 16274, (B) 16278 and (C) 16399 in D-loop of ESCC patients. Zhang et al. Journal of Experimental & Clinical Cancer Research 2010, 29:155 http://www.jeccr.com/content/29/1/155 Page 3 of 5 Discussion Selected SNPs in the D-loop region have been examined for the ability to predict cancer risk in other types of tumour [11-14]. The present study has extended those analyses to determine the cancer risk and the post- operational survival-associated germline SNPs in a con- tinuous sequence of mtDNA between nucleotides 16190 and 583 in ESCC patients. Three SNPs, 16274G/A,