Short article: Evaluation of O6-methylguanine-DNA methyltransferase as a predicting factor of response to temozolomide-based chemotherapy in well-differentiated metastatic pancreatic neuroendocrine tumors.

Abstract

Temozolomide (TMZ) is an alkylating agent frequently used in well-differentiated metastatic pancreatic neuroendocrine tumors (PNETs) with very variable responses. O-methylguanine-DNA methyltransferase (MGMT) is a DNA repair enzyme whose loss of expression has been suggested to be predictive of response to TMZ in various human tumors. We evaluated the predictive value of MGMT status, assessed by immunohistochemistry (IHC) and methylation-specific PCR (MS-PCR), in well-differentiated metastatic PNETs treated by a TMZ-based chemotherapy. All patients with metastatic PNETs treated with TMZ-based chemotherapy between 2010 and 2016 in two academic centers, for whom the tumor samples were available, were included. Clinical data were collected and the MGMT status of the tumors was analyzed using MS-PCR and IHC. Twenty-two patients (nine men, median age 61 years) were included. The loss of MGMT protein expression detected by IHC was observed in 13 (59%) patients and MGMT promoter hypermethylation was detected by MS-PCR in three (15%) out of 20 interpretable cases. MGMT status did not correlate significantly with the best radiological response according to the Response Evaluation Criteria In Solid Tumors criteria or with progression-free survival. There was no correlation between MGMT protein expression and MGMT gene promoter methylation. These results indicate that a deficient MGMT status in PNETs, determined by loss of protein expression in IHC or by the presence of MGMT gene promoter methylation measured by MS-PCR, is not associated with a better response to TMZ-based chemotherapy and cannot be used as a predictive marker to lead treatment decisions.