| 摘要: | 背景
大腸直腸癌(colorectal cancer, CRC)是台灣地區民眾第二常見的癌症，也是造成癌症死亡的第三個主要原因。CRC病患在手術之後多半會接受以5-氟尿嘧啶(5-fluorouracil, 5-FU)為基礎的化學治療。然而，個體對這些藥物的反應和相關的副作用卻常見差異性，可能是和遺傳易感受性有關。
5-FU的細胞毒性作用受到胸?酸合成?(thymidylate synthase, TYMS)、二氫嘧啶脫氫?(dihydropyrimidine dehydrogenase, DPYD)、乳清酸磷酸核糖轉移?(orotate phosphoribosyltransferase, OPRT)和亞甲基四氫葉酸還原? (methylenetetrahydrofolatereductase, MTHFR)的調控，因此5-FU的療效受到這些酵素活性的影響，人體中受到基因多形性差異，使得轉錄與轉譯能力有所不同，進而改變酵素活性。上皮生長因子接受體(epidermal growth factor receptor, EGFR)是一種跨膜糖蛋白(transmembrane glycoprotein)，可以調控多種細胞功能，當它受到活化會刺激下游基因表現，促進細胞增生(proliferation)和抑制細胞凋亡(apoptosis)，若是在訊息傳遞的過程發生調節異常(dysregulation)，通常會導致腫瘤的發生，與EGFR活性有關的基因多形性可能與CRC存活時間有關。麩胺基硫轉移酵素(GSTM1、GSTT1和GSTP1)和DNA修補酵素(XRCC1、XRCC3和XPD)在大腸直腸腫化學治療的過程，也可能扮演相當重要的角色，本研究即為著探究其相關。
方法
自1995年到2001年間總共收集了3622位經病理切片確診的CRC病患，其中有499位在手術之後接受以5-FU為基礎之化學治療，我們分析TYMS (5’-UTR 2R/3R, 5’-G/C SNP in 3R, and 3’-UTR ins6/del6)、OPRT G638C、DPYD A1267G、MTHFR (C677T and A1298C)、EGFR (R497K, G-216T and CA repeats) GSTM1、GSTT1、GSTP1 Ile105Val、XRCC1 Arg399Gln、XRCC3 Thr241Met和XPD Lys751Gln之基因多形性。我們也測量TYMS基因型和TYMS mRNA表現量的相關性。這些基因多形性與的存活分析，使用Kaplan-Meier曲線和log-rank檢定進行分析。各基因型或TYMS mRNA表現量和存活結果之間的相關性，則運用Cox比例危險模式進行分析。另外也依照性別、腫瘤位置和腫瘤期別進行分層分析。
結果
大腸癌病患帶有TYMS 5’-UTR high expression基因型組合，較low+moderate expression基因組合的有顯著較佳的總存活率(overall survival, OS)，危險對比值(hazard ratio (HR) = 0.58, 95% confidence interval (CI) = 0.35-0.96)，進一步分析可發現，大腸癌病患TYMS 5’-UTR為low+moderate expression且3’-UTR low expression比起5’-UTR為high expression且3’-UTR low expression有最差的總存活危險對比值(HR = 2.32, 95% CI = 1.20-4.51)。CRC病患帶有3RG/ins6單體型有較差的存活率(HR = 1.84)，然而大腸癌病患若帶有TYMS 2R or 3R/del6或是3RG/ins6單體型存活率較差(HR = 1.33和2.12)。
帶有MTHFR 677 C/T+T/T基因型的CRC病患，比起677 C/C基因型者有顯著較長的OS (HR = 0.79, 95% CI = 0.62-1.00)。雖然MTHFR A1298C基因多形性與CRC病患在總存活率上沒有顯著相關性，但直腸癌病患帶有1298 A/C+C/C基因型比起A/A基因型則有較短的OS (HR = 2.01, 95% CI = 1.34-2.80)。在單體型分析方面，大腸癌病患帶有MTHFR 677T-1298A單體型有較佳的存活率(HR = 0.81, 95% CI = 0.55-0.97)，然而直腸癌病患若帶有MTHFR 677C-1298C單體型存活率較差(HR = 1.58, 95% CI = 1.16-2.27)。另外，比起OPRT G/G基因型者，G/C+C/C基因型在直腸癌或是第II+III期OS較佳(HR分別為0.60和0.65)。
CRC病患若帶有EGFR (CA)n L/L基因型，比起S/S+S/L基因型有顯著較佳的OS (L, ? 20重複; S, < 20重複) (HR = 0.62, 95% CI = 0.42-0.92)，尤其是男性(HR = 0.63, 95% CI = 0.44-0.90)、第IV期(HR = 0.70, 95% CI = 0.49-0.99)、有家族癌症病史(HR = 0.55, 95% CI = 0.33-0.90)和直腸癌(HR = 0.62, 95% CI = 0.42-0.92)病患。CRC病患若同時帶有EGFR (CA)n L/L、G-216T G/G和R497K K/K基因型，比起EGFR (CA)n S對偶基因、G-216T G/G和R497K R對偶基因之基因型有較好的OS (HR = 0.51, 95% CI = 0.30-0.87)。在單體型分析方面，帶有L/G/K單體型的CRC與直腸癌病患，有較佳的存活率(HR分別為0.77與0.67)。
CRC病患若帶有XPD Gln對偶基因比起Lys/Lys基因型有較差的存活率(HR = 1.38, 95% CI = 1.02-1.87)，尤其是直腸癌病患(HR = 1.87, 95% CI = 1.18-2.95)。而在第II+III期的大腸癌病患發現，帶有XRCC1 Gln對偶基因者比起XRCC1 Arg/Arg基因型有較短的OS (HR = 1.69, 95% CI = 1.06-2.71)。第II+III期CRC病患若為XRCC1 Gln對偶基因且XPD Gln對偶基因者總存活率較差(HR = 2.60, 95% CI = 1.19-5.71)，且直腸癌病患若為XRCC1 Arg/Arg基因型且XPD Gln對偶基因者存活率亦較差(HR = 2.77, 95% CI = 1.25-6.17)。
Cox比例危險模式進行複迴歸分析發現，年齡、腫瘤期別和TYMS 3’-UTR high expression基因型與CRC病患化療後存活風險增加有關，OPRT 638C對偶基因、MTHFR 677T對偶基因和EGFR (CA)n L/L基因型則和CRC病患較佳的預後有相關。然而DYPD、GSTM1、GSTT1、GSTP1和XRCC3基因多形性和CRC病患的總存活率無相關，就算是分層分析後也無。
結論
本研究是進行回顧性研究，以探討基因多形性與CRC病患接受5-FU化學治療的存活相關性。我們發現TYMS、MTHFR、OPRT、XRCC1和XPD基因多形性可能可以當作總存活率的預測因子。就我們所知，這個研究是針對華人擁有最大樣本數的相關性研究，在對大腸直腸癌的治療選擇有創新的研究成果。
Background
Colorectal cancer (CRC) is the second most common cancer and the third leading cause of cancer deaths for population in Taiwan. Patients with CRC are often treated with 5-fluorouracil (5-FU) based chemotherapy after surgery. However, individual response and associated survival outcomes to these drugs may vary on genetic susceptibility.
The cytotoxic effect of 5-FU is mediated by the thymidylate synthase (TYMS), dihydropyrimidine dehydrogenase (DPYD), orotate phosphoribosyltransferase (OPRT), and methylenetetrahydrofolate reductase (MTHFR). The efficacy of 5-FU may depend on the activity and concentration of these enzymes. Additionally, expressions of these enzymes are determined largely by polymorphisms on their coding genes. Epidermal growth factor receptor (EGFR) is a kind of transmembrane protein, which leads to downstream effects in gene expression causing cellular proliferation and apoptosis. Therefore, dysregulation through signal pathway may induce malignant tumors and EGFR polymorphisms would be expected to correlate with CRC survival. Polymorphisms in genes encoding glutathione S-transferase enzymes (GSTM1, GSTT1 and GSTP1) and DNA repair enzymes (XRCC1, XRCC3 and XPD) may also play important roles in the response of colorectal tumor receiving chemotherapy.
Methods
Between 1995 and 2001 we totally recruited 3622 histologically confirmed CRC patients, in which 499 patients had received 5-FU-based chemotherapy after surgery. We genotyped polymorphisms for TYMS (5’-UTR 2R/3R, 5’-G>C SNP in 3R, and 3’-UTR ins6/del6), OPRT G638C, DPYD A1267G, MTHFR (C677T and A1298C), EGFR (R497K, G-216T and CA repeats), GSTM1, GSTT1, GSTP1 Ile105Val, XRCC1 Arg399Gln, XRCC3 Thr241Met, and XPD Lys751Gln. We also determined the correlation between TYMS genotypes and TYMS mRNA expression levels in tumor tissues. Survival analyses on those genetic polymorphisms for CRC survivals displayed with Kaplan-Meier curves and log-rank test. The associations between genotypes or TYMS mRNA expression and survival outcomes were analyzed using Cox proportional hazard models. Stratification analyses for gender, tumor subsite, and tumor stage were also conducted.
Results
Colon cancer patients with the 5’-UTR high-expression genotype, compared to those with low- or moderate-expression genotype, had a significantly better overall survival (OS) (hazard ratio (HR) = 0.58, 95% confidence interval (CI) = 0.35-0.96). Furthermore, colon cancer patients simultaneously harboring the 5’-UTR G>C low- or moderate-expression genotype and 3’-UTR high-expression genotype had significantly worst OS (HR = 2.32, 95% CI = 1.20-4.51), compared to those harboring the 5’-UTR G>C high-expression genotype and 3’-UTR low-expression genotype. Better survival was related to CRC patients carrying the 3RG/ins6 haplotype (HR = 1.84), but worse survival was linked to colon cancer patients carrying the TYMS 2R or 3R/del6 and 3RG/ins6 haplotype (HR = 1.33 and 2.12, respectively).
The OS was significantly longer in CRC patients with MTHFR 677 C/T+T/T genotypes compared with those with the 677 C/C genotype (HR = 0.79, 95% CI = 0.62-1.00). Although MTHFR A1298C polymorphism was not associated with OS in CRC patients, A/C+C/C genotypes showed significantly a shorter OS than those with the A/A genotype in rectal cancer patients (HR = 2.01, 95% CI = 1.34-2.80). In haplotype analysis, better survival was related to colon cancer patients carrying the MTHFR 677T-1298A haplotype (HR = 0.81, 95% CI = 0.55-0.97), but worse survival was linked to rectal cancer patients carrying the MTHFR 677C-1298C haplotype (HR = 1.58, 95% CI = 1.16-2.27). Moreover, compared to OPRT G/G genotype, G/C+C/C genotype showed a better OS in colon cancer for patients diagnosed at stage II+III patients (HR = 0.60 and HR = 0.65, respectively).
Compared to patients with the S/S+S/L genotype, CRC patients with the EGFR (CA)n L/L genotype had a significant better OS (L, ≥ 20 repeats; S, < 20 repeats) (HR = 0.62, 95% CI = 0.42-0.92), particularly for patients who were males (HR = 0.63, 95% CI = 0.44-0.90), at stage IV (HR = 0.70, 95% CI = 0.49-0.99), with family history of cancer (HR = 0.55, 95% CI = 0.33-0.90) and rectal cancer (HR = 0.62, 95% CI = 0.42-0.92). Better survival was prominent for patients with the combined genotypes of EGFR (CA)n L/L, G-216T G/G, and R497K K/K (HR = 0.51, 95% CI = 0.30-0.87) than for those with the most common genotypes of the EGFR (CA)n S allele, G-216T G/G, and R497K R allele. In haplotype analysis, better survival was related to CRC and rectal cancer patients carrying the L/G/K haplotype (HR = 0.77 and 0.67, respectively).
CRC patients with the XPD Gln allele had poorer survival than patients with the Lys/Lys genotype (HR = 1.38, 95% CI = 1.02-1.87), particular for rectal cancer patients (HR = 1.87, 95% CI = 1.18-2.95). A significant shorter OS was observed among stage II+III colon cancer patients with the XRCC1 Gln allele (HR = 1.69, 95% CI = 1.06-2.71), compared to those with the XRCC1 Arg/Arg genotype. In the combined analysis of the XRCC1 and XPD genes among stage II+III patients, the poorest OS was observed in colon cancer patients with the XRCC1 Gln and XPD Gln allele (HR = 2.60, 95% CI = 1.19-5.71) and in rectal cancer patients with the XRCC1 Arg/Arg and XPD Gln allele (HR = 2.77, 95% CI = 1.25-6.17).
In multivariate Cox proportional hazard models showed that age, TNM stage, and 3’-UTR high expression were related to wrost survival. Beside, OPRT 638C allele, MTHFR 677T allele, and EGFR (CA)n L/L genotype were related to better survival. However, DYPD, GSTM1, GSTT1, and XRCC3 polymorphisms were not associated with OS in CRC patients even in stratification analysis.
Conclusions
This study was a retrospective study to investigate association between polymorphisms and survival outcomes in CRC patients treated with 5-FU based chemotherapy. We found that the polymorphisms of TYMS, MTHFR, OPRT, XRCC1, and XPD genes might serve as OS predictors. To the best of our knowledge, this is the largest study to investigate this association for the ethnic Chinese (i.e., Taiwanese) population. We have obtained innovative findings in selecting treatment regimens for CRC patients. |
