title: Thymidylate synthase and microsatellite instability in colorectal cancer: implications for disease free survival, treatment response and survival with metastases.
abstract: BACKGROUND
  Colorectal cancer (CRC) cell lines displaying microsatellite instability (MSI) are resistant to 5-fluorouracil (5-FU) in vitro, which can be overcome by restoring DNA mismatch repair (MMR) competence. Thymidylate synthase (TS) is inhibited by 5-FU, being another potential mediator of therapeutic resistance to 5-FU. The clinical relevance of these observations remains unclear.
  
  
  OBJECTIVE
  We examined the expression of TS and two MMR proteins (hMLH1 and hMSH2) in advanced CRC patients, to determine a) their mutual relationship, b) association to therapeutic response and c) impact on disease outcome.
  
  
  METHODS
  Tumour samples from 73 patients CRC who were treated in advanced stage with either irinotecan alone or in combination with 5-FU/leucovorin, were analysed for expression of TS, hMLH1 and hMSH2 using immunohistochemistry (IHC).
  
  
  RESULTS
  TS expression was closely correlated with hMLH1 expression (negative-weak/moderate-strong) (p=0.0001). TS-MMR expression was significantly (p=0.029 for whole series; p=0.004 for the 5-FU treated cases) related to response to treatment; tumours with low levels of both TS and MMR responded better (n=14/27, 51.8%) than those with high TS and MMR (n=3/18, 16.6%). Patients with high TS-MMR expression had a significantly longer DFS (47 months vs. 9 months, n=26) than those with low TS-MMR index (p=0.015), while the reverse was true concerning survival with metastases (WMS) (p=0.018) in all the patients (n=73).
  
  
  CONCLUSIONS
  The present data suggest that MSI patients with low TS and deficient MMR demonstrate a significantly shorter DFS and longer WMS than patients with high expression of both markers, and they are also more likely to obtain the greatest benefit from 5-FU based chemotherapy.
authors.affiliation: Department of Oncology and Radiotherapy, Turku University Hospital, Turku, Savitehtaankatu 1, Finland. riyben@utu.fi
authors.forename: R
authors.initials: R
authors.lastname: Bendardaf
authors.forename: H
authors.initials: H
authors.lastname: Lamlum
authors.forename: R
authors.initials: R
authors.lastname: Ristamäki
authors.forename: E
authors.initials: E
authors.lastname: Korkeila
authors.forename: K
authors.initials: K
authors.lastname: Syrjänen
authors.forename: S
authors.initials: S
authors.lastname: Pyrhönen
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000032:analysis* / Q000187:drug effects / Q000235:genetics; D000328:Adult; D000368:Aged; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D014408:Biomarkers, Tumor / Q000032:analysis* / Q000235:genetics; D002166:Camptothecin / Q000008:administration & dosage / Q000031:analogs & derivatives; D015179:Colorectal Neoplasms / Q000201:enzymology* / Q000235:genetics* / Q000401:mortality / Q000473:pathology / Q000628:therapy; D053843:DNA Mismatch Repair / Q000187:drug effects; D018572:Disease-Free Survival; D005060:Europe / Q000453:epidemiology; D005260:Female; D005472:Fluorouracil / Q000008:administration & dosage; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007150:Immunohistochemistry; D000077146:Irinotecan; D053208:Kaplan-Meier Estimate; D008297:Male; D053842:Microsatellite Instability / Q000187:drug effects; D008875:Middle Aged; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein / Q000032:analysis* / Q000187:drug effects / Q000235:genetics; D009367:Neoplasm Staging; D009687:Nuclear Proteins / Q000032:analysis* / Q000187:drug effects / Q000235:genetics; D013940:Thymidylate Synthase / Q000032:analysis* / Q000187:drug effects / Q000235:genetics; D016896:Treatment Outcome
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D014408:Biomarkers, Tumor; C501486:MLH1 protein, human; D009687:Nuclear Proteins; D000077146:Irinotecan; D013940:Thymidylate Synthase; C497172:MSH2 protein, human; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D005472:Fluorouracil; D002166:Camptothecin