Reporter gene assay demonstrates functional differences in estrogen receptor activity in purified breast cancer cells: a pilot study

Prognostic values of negative estrogen or progesterone receptor expression in patients with luminal B HER2-negative breast cancer

BACKGROUND

The luminal subtype of breast cancer is sensitive to anti-estrogen therapy and shows a better prognosis than that of human epidermal growth factor receptor2 (HER2)-enriched or triple-negative breast cancer. However, the luminal type of breast cancer is heterogeneous and can have aggressive clinical features. We investigated the clinical implications of single hormone receptor negativity in a luminal B HER2-negative group.

METHODS

We collected luminal B HER2-negative breast cancer data that were estrogen receptor (ER) and/or progesterone receptor (PR) positive, Ki 67 high (>14 %), and HER2 negative and divided them into the ER- and PR-positive group and the ER- or PR-negative group. We analyzed the clinical and pathological data and survival according to ER or PR loss.

RESULTS

There were no statistical differences in TNM stage, breast and axillary operative methods, or number of tumors between the ER- and PR-positive group and ER- or PR-negative group. However, the ER- or PR-negative group was associated with older age (≥45 years), higher histological grade, lower Bcl-2 expression, and far higher Ki 67 (>50 %). Disease-free survival (DFS) and overall survival (OS) were shorter in the ER- or PR-negative group than that in the ER- and PR-positive group (p = 0.0038, p = 0.0071).

CONCLUSIONS

ER- or PR-negative subgroup showed worse prognosis than ER- and PR-positive subgroup in the luminal B HER2-negative group. We could consider the negativity of ER or PR as prognostic marker in luminal B HER2-negative subtype of breast cancer.

Membrane localization of insulin receptor substrate-2 (IRS-2) is associated with decreased overall survival in breast cancer

Recent studies have identified a role for insulin receptor substrate-2 (IRS-2) in promoting motility and metastasis in breast cancer. However, no published studies to date have examined IRS-2 expression in human breast tumors. We examined IRS-2 expression by immunohistochemistry (IHC) in normal breast tissue, benign breast lesions, and malignant breast tumors from the institutional pathology archives and a tumor microarray from a separate institution. Three distinct IRS-2 staining patterns were noted: diffusely cytoplasmic, punctate cytoplasmic, and localized to the cell membrane. The individual and pooled datasets were analyzed for associations of IRS-2 staining pattern with core clinical parameters and clinical outcomes. Univariate analysis revealed a trend toward decreased overall survival (OS) with IRS-2 membrane staining, and this association became significant upon multivariate analysis (P = 0.01). In progesterone receptor negative (PR-) tumors, in particular, IRS-2 staining at the membrane correlated with significantly worse OS than other IRS-2 staining patterns (P < 0.001). When PR status and IRS-2 staining pattern were evaluated in combination, PR- tumors with IRS-2 at the membrane were associated with a significantly decreased OS when compared with all other combinations (P = 0.002). Evaluation of IRS-2 staining patterns could potentially be used to identify patients with PR- tumors who would most benefit from aggressive treatment.

Tamoxifen resistance in breast tumors is driven by growth factor receptor signaling with repression of classic estrogen receptor genomic function

Not all breast cancers respond to tamoxifen, and many develop resistance despite initial benefit. We used an in vivo model of estrogen receptor (ER)-positive breast cancer (MCF-7 xenografts) to investigate mechanisms of this resistance and develop strategies to circumvent it. Epidermal growth factor receptor (EGFR) and HER2, which were barely detected in control estrogen-treated tumors, increased slightly with tamoxifen and were markedly increased when tumors became resistant. Gefitinib, which inhibits EGFR/HER2, improved the antitumor effect of tamoxifen and delayed acquired resistance, but had no effect on estrogen-stimulated growth. Phosphorylated levels of p42/44 and p38 mitogen-activated protein kinases (both downstream of EGFR/HER2) were increased in the tamoxifen-resistant tumors and were suppressed by gefitinib. There was no apparent increase in phosphorylated AKT (also downstream of EGFR/HER2) in resistant tumors, but it was nonetheless suppressed by gefitinib. Phosphorylated insulin-like growth factor-IR (IGF-IR), which can interact with both EGFR and membrane ER, was elevated in the tamoxifen-resistant tumors compared with the sensitive group. However, ER-regulated gene products, including total IGF-IR itself and progesterone receptor, remained suppressed even at the time of acquired resistance. Tamoxifen's antagonism of classic ER genomic function was retained in these resistant tumors and even in tumors that overexpress HER2 (MCF-7 HER2/18) and are de novo tamoxifen-resistant. In conclusion, EGFR/HER2 may mediate tamoxifen resistance in ER-positive breast cancer despite continued suppression of ER genomic function by tamoxifen. IGF-IR expression remains dependent on ER but is activated in the tamoxifen-resistant tumors. This study provides a rationale to combine HER inhibitors with tamoxifen in clinical studies, even in tumors that do not initially overexpress EGFR/HER2.

Biology of progesterone receptor loss in breast cancer and its implications for endocrine therapy

The response to endocrine therapy in breast cancer correlates with estrogen receptor (ER) and progesterone receptor (PR) status. ER-positive/PR-negative breast cancers respond less well to selective ER modulator (SERM) therapy than ER-positive/PR-positive tumors. The predictive value of PR has long been attributed to the dependence of PR expression on ER activity, with the absence of PR reflecting a nonfunctional ER and resistance to hormonal therapy. However, recent clinical and laboratory evidence suggests that ER-positive/PR-negative breast cancers may be specifically resistant to SERMs, whereas they may be less resistant to estrogen withdrawal therapy with aromatase inhibitors, which is a result inconsistent with the nonfunctional ER theory. Novel alternative molecular mechanisms potentially explaining SERM resistance in ER-positive/PR-negative tumors have been suggested by recent experimental indications that growth factors may downregulate PR levels. Thus, the absence of PR may not simply indicate a lack of ER activity, but rather may reflect hyperactive cross talk between ER and growth factor signaling pathways that downregulate PR even as they activate other ER functions. Therefore, ER-positive/PR-negative breast tumors might best be treated by completely blocking ER action via estrogen withdrawal with aromatase inhibitors, by targeted ER degradation, or by combined therapy targeting both ER and growth factor signaling pathways. In this review, we will discuss the biology and etiology of ER-positive/PR-negative breast cancer, highlighting recent data on molecular cross talk between ER and growth factor signaling pathways and demonstrating how PR might be a useful marker of these activities. Finally, we will consider the clinical implications of these observations.

Endocrine responsiveness: understanding how progesterone receptor can be used to select endocrine therapy

The receptor for the female hormone progesterone (PR), like that for estrogen (ER), is an important predictive marker for response to endocrine therapy in patients with breast cancer. PR exists as two isoforms, A and B. PR is important in mammary gland development and excess production of PRB is associated with breast cancer risk. Overabundance of PRA is related to resistance to tamoxifen. Total loss of PR is linked to reduced benefit from tamoxifen in both the adjuvant and metastatic settings. The predictive significance of PR expression was originally explained on the basis that PR is an ER-regulated gene and its presence indicates a functioning ER pathway and, therefore, an endocrine-responsive tumor. More recent data, however, suggest an alternative explanation. While many studies show that loss of PR predicts relative resistance to the antiestrogen tamoxifen, a recent study suggests that PR loss may not indicate resistance to aromatase inhibition. The finding that PR loss may not correlate with resistance to aromatase inhibition may be related to crosstalk between ER and PR and growth factor receptor pathways such as HER2. PR loss in some tumors is due to excessive growth factor receptor signaling (overexpression of HER2), which downregulates expression of the PR gene. Neoadjuvant studies also show that HER2 signaling is associated with tamoxifen resistance, but not resistance to aromatase inhibitors. Therefore, high HER2 signaling could explain both PR loss and resistance to tamoxifen while the response to aromatase inhibitors is maintained. In this way, PR loss in some tumors may be a surrogate marker for increased signaling through the growth factor receptor tyrosine kinase pathway and it may help clinicians decide between initial use of an aromatase inhibitor or tamoxifen in the individual patient.

Estrogen receptor-positive, progesterone receptor-negative breast cancer: association with growth factor receptor expression and tamoxifen resistance

BACKGROUND

Clinical data indicate that estrogen receptor-positive/progesterone receptor-negative (ER+/PR-) breast cancers are less sensitive to tamoxifen than are ER+/PR+ tumors. It has also been reported that tamoxifen may be less effective in tumors that overexpress either HER-2 or HER-1 (epidermal growth factor receptor) and that signaling through these receptors reduces PR expression in experimental models. We hypothesized that ER+/PR- breast tumors are more likely than ER+/PR+ breast tumors to have an aggressive phenotype, to express HER-1 and overexpress HER-2, and are less likely to benefit from tamoxifen adjuvant therapy.

METHODS

Clinical and biological features of 31 415 patients with ER+/PR+ tumors were compared with those of 13,404 patients with ER+/PR- tumors. Association between disease-free survival (DFS) and HER-1 and HER-2 status was analyzed in a subset of 11,399 patients receiving adjuvant tamoxifen therapy. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated using Cox regression or Kaplan-Meier analyses, and all statistical tests were two-sided.

RESULTS

ER+/PR- tumors were more frequent in older patients, were larger in size, had a higher S-phase fraction, and were more likely to be aneuploid than ER+/PR+ tumors. Furthermore, three times as many ER+/PR- tumors as ER+/PR+ tumors expressed HER-1 (25% versus 8%; P < .001) and 50% more overexpressed HER-2 (21% versus 14%; P < .001). Among all tamoxifen-treated women, recurrence was higher among women with HER-1-expressing tumors than with HER-1-negative tumors (HR = 1.9, 95% CI = 1.0 to 3.5; P = .05); a stronger association between worse DFS and HER-2 overexpression was observed (HR = 2.3, 95% CI = 1.2 to 4.3; P = .006). However, results varied by PR status. Among tamoxifen-treated women with ER+/PR+ tumors, HER-1 or HER-2 status was not associated with worse DFS. Among women with ER+/PR- tumors, however, both HER-1 expression (HR = 2.4, 95% CI = 1.0 to 5.4; P = .036) and HER-2 overexpression (HR = 2.6, 95% CI = 1.1 to 6.0; P = .022) were associated with a higher likelihood of recurrence.

CONCLUSIONS

ER+/PR- tumors express higher levels of HER-1 and HER-2 and display more aggressive features than ER+/PR+ tumors. As in laboratory models, lack of PR expression in ER+ tumors may be a surrogate marker of aberrant growth factor signaling that could contribute to the tamoxifen resistance observed in these tumors.