Progesterone receptor B (PRB) promoter hypermethylation in sporadic breast cancer: progesterone receptor B hypermethylation in breast cancer.
BACKGROUND
Oestrogen receptor alpha (ER alpha) is traditionally measured on all breast tumour specimens to identify those patients more likely to respond to anti-oestrogens. Progesterone receptor (PR) status has contributed useful information in defining more responsive subgroups. PR negativity may be a marker for increased signalling through growth factor receptor tyrosine kinase pathways. Progesterone acts through two PRs, PRA and PRB. PRB, the functionally active PR, can be silenced by promoter hypermethylation.


METHODS
Following DNA and RNA extraction from 94 breast carcinomas, the methylation status of the PRB promoter was assessed by sodium bisulphite modification and methylation sensitive PCR (MSP). A quantitative realtime PCR analysis (QRTPCR) was used to determine the levels of PRB mRNA expression. Protein expression was evaluated immunohistochemically with a commercially available PRB antibody.


RESULTS
76% of the primary breast carcinoma samples demonstrated a methylated band for PRB. PRB methylation significantly compromised total PR immunohistochemistry (IHC) expression (P = 0.03). PRB mRNA correlated positively with total PR IHC (r = 0.58, P = 0.04), ER alpha IHC (P = 0.02), and tumour grade (P = 0.01). PRB protein expression was significantly associated with a number of favourable prognostic variables including smaller (P = 0.004) lower grade (P = 0.007), ER alpha IHC positive tumours (P < 0.001), and tumours with a low Nottingham Prognostic Index (NPI) (P = 0.0008). PRB mRNA levels were significantly associated with better overall survival (P = 0.04) in a univariate analysis.


CONCLUSIONS
The majority of tumours were methylated for PRB. This did not directly compromise PRB expression suggesting that other factors may down regulate the PR gene. When PRB was expressed, it correlated with good prognostic markers and better overall survival.
Mc Cormack
Orla
O
The Adelaide and Meath Hospital, Dublin Incorporating the National Childrens Hospital, Tallaght, Dublin, 24, Ireland. omccormack@rcsi.ie
Chung
Wen Y
WY
Fitzpatrick
Patricia
P
Cooke
Fiachra
F
Flynn
Barbara
B
Harrison
Michele
M
Fox
Edward
E
Gallagher
Emma
E
McGoldrick
Aloysius
A
Dervan
Peter A
PA
McCann
Amanda
A
Kerin
Michael J
MJ
D001483:Base Sequence; D014408:Biomarkers, Tumor / Q000032:analysis*; D001943:Breast Neoplasms / Q000235:genetics* / Q000401:mortality / Q000473:pathology*; D019175:DNA Methylation; D047628:Estrogen Receptor alpha / Q000096:biosynthesis; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D011379:Prognosis; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D011980:Receptors, Progesterone / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D014408:Biomarkers, Tumor; D047628:Estrogen Receptor alpha; D012333:RNA, Messenger; D011980:Receptors, Progesterone; C097314:progesterone receptor B