Book of abstract 2008

Markers predicting clinical outcome in breast cancer patients treated
with anti-estrogen therapy: towards the identification of biologically and
clinically relevant information
Maria Grazia Daidone, Danila Cordini, Valeria Musella, Loris De Cecco, Maya Fedeli,
Manuela Gariboldi, Patrizia Miodini, Vera Cappelletti, Marco Pierotti
Foundation IRCCS – National Institute of Tumors, Milano, Italy
In estrogen receptor positive (ER+) breast cancer patients, the identification of molecular
markers predictive of early relapse following anti-estrogen treatment still represents an
investigational open question. We evaluated the expression of RERG (Ras-related, estrogenregulated
and growth-inhibitor, a unique estrogen-dependent regulated protein belonging
to the Ras superfamily of GTP-binding proteins) by quantitative real-time-PCR in 113
ER+ primary breast cancers from patients subjected to surgery and adjuvant tamoxifen,
and investigated its relationship with some patho-biological factors (including tumor
size, grade and histology, lymph node involvement, ER and progesterone receptor [PgR]
levels) and biomarkers indicative of a typical luminal phenotype (GATA3) or known to
be associated with tamoxifen resistance (HER-2/neu and PTEN). RERG expression was
significantly associated with hormone-related factors: in fact, it was positively correlated
with both mRNA and the corresponding protein level of ER and PgR and with GATA3,
which codes for a transcription factor recently shown to be involved in the positive
regulation of the expression of ERS1 gene in a cross-regulatory feedback loop. Conversely,
no association was found between RERG and PTEN or HER-2 mRNA expression, thus
indicating an independence of molecular mechanisms of cell response to hormones and
anti-hormones involving these genes.
Follow-up analysis indicates that reduced RERG mRNA expression was present in
tumors from women that will develop relapse compared to those long-term disease-free.
The association of RERG expression with patients outcome was independent of the
most important patho-biologic features of prognostic relevance following anti-estrogen
treatment: lymph nodal
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involvement, PgR status and ER content. In a multivariate Cox’s
proportional hazard regression analysis a low RERG expression was a significant predictor
of relapse occurrence (hazard ratio [HR] for low versus high 2.084, 95% confidence
interval [CI] 1.092-3.979, P=0.026), similarly to GATA3 expression (HR for low versus
high 2.570, 95% CI 1.301-5.077, P=0.0066). Conversely, HER-2 and PTEN failed to
provide prognostic information. Low expression of RERG associated with low GATA3 in
PgR-negative tumors identified patients with the worse prognosis, even after adjustment
for lymph node involvement and ER content.
RERG contribution to anti-estrogen cell response was also supported by in vitro data.
In fact, in MDA-MB361 and MCF7 cells, two ER-positive cell lines responsive to the
antiproliferative effect of anti-estrogens, the growth inhibition by 4-OH-tamoxifen was
paralleled by an increase in RERG mRNA expression while the lack of proliferative effect
observed in ZR-75.1 was accomplished by a progressive down-regulation of the gene
expression suggesting that RERG may be involved in mediating the growth-inhibitory
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