title: O6-methylguanine DNA methyltransferase deficiency and response to temozolomide-based therapy in patients with neuroendocrine tumors.
abstract: OBJECTIVE
  Recent studies suggest that temozolomide has activity in neuroendocrine tumors. Low levels of the DNA repair enzyme, O(6)-methylguanine DNA methyltransferase (MGMT), are associated with sensitivity to temozolomide in other tumor types. We evaluated the prevalence of MGMT deficiency in neuroendocrine tumors and correlated MGMT deficiency with treatment response to temozolomide-based regimens.
  
  
  METHODS
  The prevalence of MGMT deficiency, measured by immunohistochemistry, was assessed in 97 archival neuroendocrine tumor specimens. Rates of treatment response and survival were next evaluated in a cohort of 101 consecutive neuroendocrine tumor patients who had received treatment with a temozolomide-based regimen at one of three institutions. MGMT expression was directly correlated with treatment response in 21 patients who had available tumor tissue and response data.
  
  
  RESULTS
  In archival specimens, MGMT deficiency was observed in 19 of 37 (51%) pancreatic neuroendocrine tumors and 0 of 60 (0%) carcinoid tumors (P < 0.0001). In the clinical cohort, 18 of 53 (34%) patients with pancreatic neuroendocrine tumors but only 1 of 44 (2%) patients with carcinoid tumors (P < 0.001) experienced a partial or complete response to temozolomide-based therapy. Among 21 patients with evaluable tumor tissue who had also received treatment with temozolomide, 4 of 5 patients with MGMT-deficient tumors (all pancreatic neuroendocrine tumors) and 0 of 16 patients with tumors showing intact MGMT expression responded to treatment (P = 0.001).
  
  
  CONCLUSIONS
  MGMT deficiency, measured by immunohistochemistry, is more common in pancreatic neuroendocrine tumors than in carcinoid tumors as is treatment response to temozolomide-based therapy. Absence of MGMT may explain the sensitivity of some pancreatic neuroendocrine tumors to treatment.
authors.affiliation: Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA 02115, USA. matthew_kulke@dfci.harvard.edu
authors.forename: Matthew H
authors.initials: MH
authors.lastname: Kulke
authors.forename: Jason L
authors.initials: JL
authors.lastname: Hornick
authors.forename: Christine
authors.initials: C
authors.lastname: Frauenhoffer
authors.forename: Susanne
authors.initials: S
authors.lastname: Hooshmand
authors.forename: David P
authors.initials: DP
authors.lastname: Ryan
authors.forename: Peter C
authors.initials: PC
authors.lastname: Enzinger
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Meyerhardt
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Clark
authors.forename: Keith
authors.initials: K
authors.lastname: Stuart
authors.forename: Charles S
authors.initials: CS
authors.lastname: Fuchs
authors.forename: Mark S
authors.initials: MS
authors.lastname: Redston
mesh_terms: D018906:Antineoplastic Agents, Alkylating / Q000627:therapeutic use; D002276:Carcinoid Tumor / Q000188:drug therapy / Q000201:enzymology; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000627:therapeutic use; D018572:Disease-Free Survival; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018358:Neuroendocrine Tumors / Q000188:drug therapy* / Q000201:enzymology*; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000172:deficiency*; D010190:Pancreatic Neoplasms / Q000188:drug therapy / Q000201:enzymology; D000077204:Temozolomide; D016896:Treatment Outcome
chemical_list: D018906:Antineoplastic Agents, Alkylating; D003606:Dacarbazine; D019853:O(6)-Methylguanine-DNA Methyltransferase; D000077204:Temozolomide