Membrane-associated Estrogen Receptors in Breast Cancer

Institution: University of California, Los Angeles
Investigator(s): Richard Pietras, M.D., Ph.D. -
Award Cycle: 2009 (Cycle 15) Grant #: 15IB-0058 Award: $149,119
Award Type: IDEA
Research Priorities
Biology of the Breast Cell>Pathogenesis: understanding the disease



Initial Award Abstract (2009)

Estrogens are hormones that are well known to promote breast cancer. These effects are exerted by the binding of estrogens to tumor cell proteins termed estrogen receptors (ER). These receptors were once thought to occur only in the cell nucleus, and detection of ERs in the nucleus is the basis of the “ER assay” used in the clinic to plan patient care. However, it is now known that ERs also occur outside the nucleus, with numerous studies showing that ERs at or near the tumor cell surface membrane (termed mERs) serve important roles in activating signals inside the tumor cell that stimulate gene changes and tumor growth.

The current ER assay that measures only nuclear ER fails to predict responses to endocrine therapy in about half of patients with advanced breast cancers, thus indicating an urgent need to improve ER assays. This may be possible by developing new assays to correlate not only nuclear ER but also mER with patient outcome. The primary aim of this project is to study archival human tumor specimens in order to design innovative assays to measure mER and to combine this clinical data with nuclear ER assays. For these studies, preserved tumor specimens (initially collected at the time of surgery) from 75 patients with primary breast cancer will be obtained, including samples from 10 patients with tissues for comparison from the primary tumor, paired metastases (spread to lymph nodes or distant organs) and nearby normal tissue. Tissue specimens will be cut in small sections and mounted on slides to test different methods for optimal detection of mER. For these studies, antibody molecules that specifically bind estrogen receptors will be used. Antibodies will be labeled with probes to allow visualization of microscopic deposits that mark the location of mERs under fluorescent and light microscopy. With successful detection of mER expression, correlation of data with nuclear ER assays and with outcome data will be done to assess prognostic benefit and predictive value for patient responses to hormonal therapies. Laboratory studies will be done to isolate and characterize molecular properties of tumor cells with high mER levels to understand how the mERs function.

Since mERs regulate breast cancer gene expression and progression, an assay to detect mER may augment current prognostic data based only on nuclear ER and improve patient management decisions and survival. Further understanding of mER activity may also lead to new therapeutic interventions.




Final Report (2010)

Estrogens are hormones that are well known to promote breast cancer. These effects are exerted by binding of estrogens to tumor cell proteins termed estrogen receptors (ER). These receptors were once thought to occur only in the cell nucleus, and detection of ERs in the nucleus is the basis of the "ER assay" used in the clinic to plan patient care. However, it is now known that ERs also occur outside the nucleus, with studies showing that extranuclear ERs (exERs) activate signals inside the tumor cell that stimulate gene changes and tumor growth. The current ER assay that measures only nuclear ER fails to predict responses to endocrine therapy in half of patients with advanced breast cancer. To improve current ER assays, we plan to develop new ways to correlate not only nuclear ER but also exER with patient outcome.

A primary aim of this project was to study archival human tumor specimens to design innovative assays to measure exER and combine this clinical data with nuclear ER assays. Preserved tumor specimens (initially collected at the time of surgery) from 76 patients with primary breast cancer were obtained, with 20 primary tumors of early stage and 56 tumors of advanced stage. Of advanced tumors, 56 include primary tumors and paired metastases. Thus, the overall collection numbers 132 tumor biopsy samples and exceeds the number of specimens expected in the original proposal.' Tissue samples were cut in small sections and mounted on slides to test different methods and antibodies for optimal detection of exER. Selected antibodies were labeled with probes to visualize microscopic deposits to mark the location of exERs under microscopy. Analyses of data from the first sets of these specimens provide evidence that:

  1. exER is expressed in primary and metastatic tumors in the clinic and may provide complementary prognostic information;
  2. expression of nuclear ER in primary tumors appears to be lost in a significant number of paired metastases;
  3. a second form of ER termed ER-beta is expressed in triple-negative breast cancers (that lack the classical nuclear ER) and may have prognostic value.

Due to the large number of specimens collected, we are continuing to correlate exER with clinical outcome data. Laboratory studies to isolate and examine properties of tumor cells with high exER levels show that these cells constitute about 5% of the bulk tumor population and co-express biomarkers detected in tumor progenitor cells. Breast cancer cell subsets that overexpess exER exhibit enhanced growth and tamoxifen resistance in vivo as compared to bulk tumor cells.

We plan to continue studies to refine an exER assay and ascertain its clinical utility. Since exERs regulate breast cancer progression, assays to detect exER may augment current prognostic data based only on nuclear ER and improve patient management decisions and survival. Further understanding of exER activity may also lead to new therapeutic interventions in the clinic particularly in metastatic and tri le-negative cancers.




Symposium Abstract (2010)

RJ Pietras (PI), DC Marquez-Garban, L Goodglick, M Fishbein, D Elashoff, J Klein.

Estrogens are hormones that are well known to promote breast cancer. These effects are exerted by the binding of estrogens to tumor cell proteins termed estrogen receptors (ER). These receptors were once thought to occur only in the cell nucleus, and detection of ERs in the nucleus is the basis of the “ER assay” used in the clinic to plan patient care. However, it is now known that ERs also occur outside the nucleus, with numerous studies showing that ERs at or near the tumor cell surface membrane (termed mERs) serve important roles in activating signals inside the tumor cell that stimulate gene changes and tumor growth.

The current ER assay that measures only nuclear ER fails to predict responses to endocrine therapy in about half of patients with advanced breast cancers, thus indicating an urgent need to improve ER assays. This may be possible by developing new assays to correlate not only nuclear ER but also mER with patient outcome. As a primary aim of this project, we are studying archival human tumor specimens in order to design innovative assays to measure mER and to combine this clinical data with nuclear ER assays. For these studies, preserved tumor specimens (initially collected at the time of surgery) from 75 patients with primary breast cancer are being obtained, including samples from 10 patients with tissues for comparison from the primary tumor, paired metastases (spread to lymph nodes or distant organs) and nearby normal tissue. Tissue specimens are cut in small sections and mounted on slides to test different methods for optimal detection of mER. For these studies, antibody molecules that specifically bind estrogen receptors are being used. Antibodies are labeled with probes to allow visualization of microscopic deposits that mark the location of mERs under fluorescent and light microscopy. We have achieved detection of mER expression and are beginning to correlate data with nuclear ER assays and with outcome data in order to assess prognostic benefit and predictive value for patient responses to hormonal therapies. Laboratory studies are also being done in parallel to isolate and characterize molecular properties of tumor cells with high mER levels to understand how the mERs function. Initial findings suggest that breast tumor cells with a high density of membrane-associated ER constitute a small subset of the bulk tumor population and co-express biomarkers commonly detected in tumor progenitor cells.

Since mERs regulate breast cancer gene expression and progression, assays to detect mER may augment current prognostic data based only on nuclear ER and improve patient management decisions and survival. Further understanding of mER activity may also lead to new therapeutic interventions in the clinic.



Extranuclear Estrogen Receptors in Breast Cancer.
Periodical:Cancer Research
Index Medicus: Cancer Res
Authors: Márquez-Garbán DC, Chen HW, Goodglick L, Fishbein MC, Pietras RJ
Yr: 2010 Vol: 70 Nbr: 24 (suppl) Abs: 310 Pg: