Prevalence and clinicopathologic correlates of o6-methylguanine- dna methyltransferase methylation status in patients with triple-negative breast cancer treated preoperatively by alkylating drugs

Background Predictive factors of benefit from specific chemotherapy regimens are not currently available in triple-negative breast cancer (TNBC). MGMT (O6-methylguanine-DNA methyltransferase) controls DNA repair pathways, and its epigenetic silencing is used for predicting the response to the alkylating drug temozolomide in patients with glioma. Materials and Methods The study population was composed of 84 patients with TNBC treated with alkylating agents and evaluated for clinicopathologic parameters (tumor shrinkage and pathologic complete response [pCR]). MGMT methylation status was assessed in formalin-fixed, paraffin-embedded tumor specimens by pyrosequencing. The samples were categorized as methylated (mean methylation value > 5%), indeterminate (4%-5%), and unmethylated ( 643%). Results MGMT methylation status was successfully evaluated in all the cases: 58.3% were methylated; 27.4%, unmethylated; and 14.3%, indeterminate. MGMT methylation was observed in 80%, 62%, and 29% of patients showing a 100%, 99% to 30%, and