Clinical significance of promoter hypermethylation of DNA repair genes in tumor and serum DNA in invasive ductal breast carcinoma patients.
OBJECTIVE
The clinical relevance of frequent methylation of CpG islands of key cancer genes in breast cancer is being increasingly recognized. Our study aimed to evaluate the promoter methylation status of DNA repair genes-BRCA1MGMT and GSTP1 in tumor and circulating DNA of invasive ductal breast carcinoma patients.


METHODS
Methylation-specific PCR was carried out to investigate the promoter methylation status of genes in tumor and circulating DNA of 100 breast cancer patients in a prospective study. The effect of promoter methylation on protein expression was evaluated by immunohistochemistry.


RESULTS
The frequency of tumor hypermethylation was 27% in BRCA1, 32% in MGMT and 25% in GSTP1 and correlated with methylation of these genes in paired serum DNA. Immunohistochemical analysis showed no detectable expression of BRCA1 and MGMT in 51/89 (57%) and 35/89 (39%) tumors, respectively. MGMT promoter methylation mediated gene silencing was associated with loss of its protein expression (p=0.002, O.R.=4.5, 95% C.I.=1.7-12.0). BRCA1 promoter methylation was not associated with loss of its protein expression, indicating that methylation is not the sole mechanism accounting for the loss/reduced BRCA1 protein expression. Importantly, GSTP1 and BRCA1 hypermethylation were found to be independent of other prognostic factors in predicting disease recurrence (p=0.02, HR=7.6, 95% C.I.=1.4-44.1; p=0.04, HR=6.2, 95% C.I.=1.1-35.7).


CONCLUSIONS
Our study underscores the potential utility of DNA methylation of these genes in serum as a promising biomarker and can serve as a surrogate for tumor DNA methylation for diagnosis and prognosis of breast cancer.
Sharma
Gayatri
G
Department of Biochemistry, All India Institute of Medical Sciences, Ansari Nagar, New Delhi 110029, India.
Mirza
Sameer
S
Parshad
Rajinder
R
Srivastava
Anurag
A
Gupta
Siddartha Datta
SD
Pandya
Pranav
P
Ralhan
Ranju
R
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019313:BRCA1 Protein / Q000235:genetics* / Q000378:metabolism; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D018270:Carcinoma, Ductal, Breast / Q000235:genetics* / Q000473:pathology; D016022:Case-Control Studies; D019175:DNA Methylation; D015254:DNA Modification Methylases / Q000235:genetics* / Q000378:metabolism; D045643:DNA Repair Enzymes / Q000235:genetics* / Q000378:metabolism; D004273:DNA, Neoplasm / Q000378:metabolism; D005260:Female; D005500:Follow-Up Studies; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D051549:Glutathione S-Transferase pi / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local; D016133:Polymerase Chain Reaction; D011379:Prognosis; D011401:Promoter Regions, Genetic; D011446:Prospective Studies; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism; D055815:Young Adult
D019313:BRCA1 Protein; D004273:DNA, Neoplasm; D025521:Tumor Suppressor Proteins; D015254:DNA Modification Methylases; C515491:MGMT protein, human; C496556:GSTP1 protein, human; D051549:Glutathione S-Transferase pi; D045643:DNA Repair Enzymes