Impact of combining the progesterone receptor and preoperative endocrine prognostic index (PEPI) as a prognostic factor after neoadjuvant endocrine therapy using aromatase inhibitors in postmenopausal ER positive and HER2 negative breast cancer

Tailoring neoadjuvant systemic therapy in breast cancer: "The advent of a personalized approach"-The Breast-Gynecological and Immuno-Oncology International Cancer Conference (BGICC) consensus and recommendations

BACKGROUND

The management of early breast cancer (BC) has witnessed an uprise in the use of neoadjuvant therapy and a remarkable reshaping of the systemic therapy postneoadjuvant treatment in the last few years, with the evolution of many controversial clinical situations that require consensus.

METHODS

During the 14th Breast-Gynecological and Immuno-Oncology International Cancer Conference held in Egypt in 2022, a panel of 44 BC experts from 13 countries voted on statements concerning debatable challenges in the neo/adjuvant treatment setting. The recommendations were subsequently updated based on the most recent data emerging. A modified Delphi approach was used to develop this consensus. A consensus was achieved when ≥75% of voters selected an answer.

RESULTS AND CONCLUSIONS

The consensus recommendations addressed different escalation and de-escalation strategies in the setting of neoadjuvant therapy for early BC. The recommendations recapitulate the available clinical evidence and expert opinion to individualize patient management and optimize therapy outcomes. Consensus was reached in 63% of the statements (52/83), and the rationale behind each statement was clarified.

Risk factors for recurrence in patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative early breast cancer in Japan: a systematic literature review and meta-analysis

BACKGROUND

The clinicopathological factors indicating risk of recurrence are used to guide the choice of perioperative therapy in patients with breast cancer. Although several risk factors for recurrence have been reported in patients with hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) early breast cancer in Japan, there has been no systematic review quantifying potential risk factors.

METHODS

We performed a systematic literature review and meta-analysis using the MEDLINE, Embase, Cochrane CENTRAL, and Japan Medical Abstract Society databases to identify risk factors for recurrence in HR+/HER2- early breast cancer in Japan. The primary outcome was relapse-free or disease-free survival (RFS/DFS), and the secondary outcomes were overall survival and breast cancer-specific survival (BCSS).

RESULTS

Searches identified 42 eligible publications. Meta-analyses identified lymph node metastasis (hazard ratio: 2.76 [95% confidence interval: 1.97-3.88]), large tumor size (1.67 [1.24-2.23]), high histological grade (1.50 [1.04-2.16]), and high nuclear grade (2.02 [1.61-2.54]) as risk factors for RFS/DFS. Lymph node metastasis (2.43 [1.28-4.63]), large tumor size (1.80 [1.24-2.62]), and high histological grade (2.02 [1.44-2.84]) were also risk factors for overall survival, and high progesterone status was a possible favorable prognostic factor for BCSS (0.20 [0.10-0.42]).

CONCLUSIONS

Identified risk factors were consistent with the previous reports, and this study provides quantitative summary of risk factors for HR+/HER2- early breast cancer recurrence in Japan. (PROSPERO Registration ID, CRD42022338391.).

Pathology of neoadjuvant therapy and immunotherapy testing for breast cancer

Neoadjuvant chemotherapy (NACT) has become the standard of care for high-risk breast cancer, including triple-negative (TNBC) and HER2-positive disease. As a result, handling and reporting of breast specimens post-NACT is part of routine practice, and it is important for pathologists to recognise the changes in tumour cells, tumour-associated stroma and background breast tissue induced by NACT. Familiarity with characteristic stromal features enables identification of the pre-treatment tumour site and allows confident diagnosis of pathological complete response (pCR) which is important for decisions concerning adjuvant therapy. Neoadjuvant endocrine therapy (NAET) is used less frequently than NACT; however, the SARS-COVID-19 pandemic has changed practice, with increased use as bridging therapy if surgery is delayed. NAET also induces characteristic changes in the tumour and stroma. Changes in the tumour microenvironment following NACT and NAET are also described. Immunotherapy is approved for use in advanced TNBC, and there are several trials exploring its role in early TNBC in the neoadjuvant setting. The current biomarker to determine eligibility for treatment with immune checkpoint inhibitors is programmed death ligand-1 (PD-L1) immunohistochemistry; however, this is complicated by lack of standardisation with different drugs linked to tests using different antibodies with different scoring systems. The situation in the neoadjuvant setting is further complicated by improved pCR rates for PD-L1-positive tumours in both immune therapy and placebo arms. Alternative biomarkers are urgently needed to identify which patients will derive benefit from immunotherapy and key candidates are discussed.

Biomarker Alteration after Neoadjuvant Endocrine Therapy or Chemotherapy in Estrogen Receptor-Positive Breast Cancer

In estrogen receptor (ER)-positive breast cancer, changes in biomarker expression after neoadjuvant therapy indicate the therapeutic response and are prognostic. However, there is limited information about the biomarker alteration caused by neoadjuvant endocrine therapy in ER-positive and human epidermal growth factor receptor 2 (HER2)-negative breast cancer. We recruited ER-positive/HER2-negative breast cancer patients who received neoadjuvant chemotherapy (NCT), neoadjuvant endocrine therapy (NET), or sequential neoadjuvant endocrine-chemotherapy (NECT) at Peking University Cancer Hospital from 2015 to 2021. A total of 579 patients had paired immunohistochemistry information in both diagnostic biopsy samples and post-neoadjuvant therapy surgical samples. Through a paired comparison of the immunohistochemical information in pre-treatment and post-treatment samples, we found that progesterone receptor (PR) expression reductions were more frequent than ER expression reductions (70.8% vs. 35.2%) after neoadjuvant therapy. The percentage of patients who had a decreased Ki-67 index in the post-operative samples was similar in the three groups (79.8% vs. 79.7% vs. 78.4%). Moreover, PR losses caused by NET were related to low baseline PR expression (p = 0.001), while we did not find a significant association between PR losses and Ki-67 reductions (p = 0.428) or ER losses (p = 0.274). All three types of neoadjuvant therapies caused a reduction in ER, PR, and Ki-67 expression. In conclusion, we found that PR loss after NET was only significantly related to low baseline PR expression, and there is no significant difference in the extent of prognostic factor change including Ki-67 and ER between the PR loss and non-loss groups.

Neoadjuvant endocrine therapy for strongly hormone receptor-positive and HER2-negative early breast cancer: results of a prospective multi-center study

PURPOSE

For estrogen receptor (ER)-positive breast cancer, neoadjuvant endocrine therapy (NET) has been shown to be as effective as neoadjuvant chemotherapy (NACT). We evaluated the prognostic significance of Preoperative Endocrine Prognostic Index (PEPI).

METHODS

We conducted a prospective, multi-center, non-randomized, controlled trial that enrolled postmenopausal early-stage strongly ER-positive (≥ 50%) and HER2-negative breast cancer patients. All patients were given 4-month NET before surgery. The primary objective was to investigate the 5-year recurrence-free survival (RFS) in patients who had PEPI 0-1 or pathological complete response (pCR) without chemotherapy. Patients who had PEPI 0-1 or pCR were recommended to receive adjuvant endocrine therapy only and patients had PEPI ≥ 2 may receive adjuvant chemotherapy at the discretion of the treating physician.

RESULTS

A total of 410 patients were included and 352 patients constituted the per-protocol population. Overall, 9 patients (2.5%) had pCR (ypT0/is ypN0), 128 patients (36.4%) had PEPI = 0, and 56 patients (15.9%) had PEPI = 1. After a median follow-up of 60 months (4-104 months), patients who had PEPI 0-1 or pCR showed an improved 5-year RFS [99.5% (95% CI 98.5-99.9%) for PEPI 0-1 or pCR group vs. 93.7% (95% CI 89.6-97.8%) for PEPI ≥ 2 group, P = 0.028]. No survival difference was detected between patients received adjuvant chemotherapy vs. no chemotherapy among PEPI ≥ 2 cases.

CONCLUSION

PEPI 0-1 or pCR may be used to define a group of ER-positive and HER2-negative postmenopausal early breast cancer patients with low relapse risk for whom adjuvant chemotherapy can be safely withheld. Studies on the identification and alternative treatment options for endocrine-resistant tumors are warranted.

CLINICAL TRIAL REGISTRATION

NCT01613560.

Association of L-type amino acid transporter 1 (LAT1) with the immune system and prognosis in invasive breast cancer

L-type amino acid transporter 1 (LAT1), also referred to as SLC7A5, is believed to regulate tumor metabolism and be associated with tumor proliferation. In invasive breast cancer, we clinicopathologically investigated the utility of LAT1 expression. LAT1 expression was evaluated via immunohistochemistry analyses in 250 breast cancer patients undergoing long-term follow-up. We assessed the relationships between LAT1 expression and patient outcomes and clinicopathological factors. Breast cancer-specific survival stratified by LAT1 expression was assessed. Human epidermal growth factor receptor 2 (HER2)-positive patients with metastasis received trastuzumab therapy. The density of tumor-infiltrating lymphocytes (TILs) was evaluated according to the International Working Group guidelines. In the current study, high LAT1 expression was significantly correlated with estrogen receptor (ER) negativity, progesterone receptor negativity, high histological grade, increased TILs, and programmed death ligand 1 positivity. Among the ER-positive and HER2-negative patients, high LAT1 was an independent indicator of poor outcomes (hazard ratio (HR) = 2.97; 95% confidence interval (CI), 1.16-7.62; p = 0.023). Moreover, high LAT1 expression was an independent poor prognostic factor in luminal B-like breast cancer with aggressive features (HR = 3.39; 95% CI 1.35-8.52; p = 0.0094). In conclusion, high LAT1 expression could be used to identify a subgroup of invasive breast cancer characterized by aggressive behavior and high tumor immunoreaction. Our findings suggest that LAT1 might be a candidate therapeutic target for breast cancer patients, particularly those with luminal B-like type breast cancer.

Prognostic value of tumor-infiltrating lymphocytes in estrogen receptor-positive and human epidermal growth factor receptor 2-negative breast cancer

Tumor-infiltrating lymphocytes (TILs) are a significant prognostic factor in triple-negative breast cancer. However, the clinicopathological significance of TILs in estrogen receptor (ER)-positive and human epidermal growth factor receptor 2 (HER2)-negative breast cancer remains unclear. The purpose of the present study was to evaluate the role of TILs in the prognosis of ER-positive and HER2-negative breast cancer. A total of 65 consecutive patients with ER-positive and HER2-negative breast cancer were examined. TILs in stromal tissue (str-TILs) were graded using the International TILs Working Group criteria. The association between several clinicopathological factors and TIL grade were investigated, and the prognostic impact of TILs was compared between luminal A-like and luminal B-like breast cancer. A total of 51 patients (78.5%) had low-grade (0-10%), 11 (16.9%) had intermediate (10-40%) and 3 (4.6%) had high-grade (40-90%) str-TIL levels. There was a significant association between high levels of Ki67 expression and a high str-TIL count. Relapse-free survival was significantly worse in patients with luminal B-like cancer compared with that in patients with luminal A-like cancer. Patients with an intermediate or high str-TIL count had a better prognosis compared with those with a low str-TIL count. All patients with luminal B-like cancer and intermediate or high str-TIL levels developed no recurrence during follow-up. In conclusion, there was a significant correlation between high-grade str-TIL levels and high tumor cell proliferation rate, as well as high levels of Ki67 expression.

Using Breast Cancer Gene Expression Signatures in Clinical Practice: Unsolved Issues, Ongoing Trials and Future Perspectives

The development of gene expression signatures since the early 2000's has offered standardized assays to evaluate the prognosis of early breast cancer. Five signatures are currently commercially available and recommended by several international guidelines to individualize adjuvant chemotherapy decisions in hormone receptors-positive/HER2-negative early breast cancer. However, many questions remain unanswered about their predictive ability, reproducibility and external validity in specific populations. They also represent a new hope to tailor (neo)adjuvant systemic treatment, adjuvant radiation therapy, hormone therapy duration and to identify a subset of patients who might benefit from CDK4/6 inhibitor adjuvant treatment. This review will highlight these particular issues, address the remaining questions and discuss the ongoing and future trials.

The Present and Future of Neoadjuvant Endocrine Therapy for Breast Cancer Treatment

Simple Summary

The treatment of breast cancer has evolved considerably over the last two decades, leading toward individualized disease management. Hormone-sensitive breast cancers constitute the vast majority of cases and endocrine therapy is the mainstay of their treatment. On the other hand, neoadjuvant or pre-surgical treatments provide a number of advantages for tumor management. In this review we will discuss the existing evidence on neoadjuvant endocrine therapy, as well as its possible future indications.

Abstract

Endocrine therapy (ET) has established itself as an efficacious treatment for estrogen receptor-positive (ER+) breast cancers, with a reduction in recurrence rates and increased survival rates. The pre-surgical approach with chemotherapy (NCT) has become a common form of management for large, locally advanced, or high-risk tumors. However, a good response to NCT is not usually expected in ER+ tumors. Good results with primary ET, mainly in elderly women, have encouraged studies in other stages of life, and nowadays neoadjuvant endocrine treatment (NET) has become a useful approach to many ER+ breast cancers. The aim of this review is to provide an update on the current state of art regarding the present and the future role of NET.

Neoadjuvant endocrine therapy in women with operable breast cancer: A retrospective analysis of real-world use

BACKGROUND

A retrospective study of the real-world use of neoadjuvant endocrine therapy (NET) is important for standardizing its role in breast cancer care.

MATERIALS AND METHODS

In a consecutive series of women with operable breast cancer who received NET for ≥28 days, NET objectives, NET outcomes, adjuvant chemotherapy use after NET, and survivals, were examined for the correlation with clinicopathological factors.

RESULTS

NET objectives were for surgery extent reduction in 49 patients, surgery avoidance in 31, and treatment until scheduled surgery in 8. The mean duration of NET was 349.5 (range, 34-1923), 869.8 (range, 36-4859), and 55.8 (range, 39-113) days in the above cohorts (success: 79.6%, 64.5%, and 100%), respectively, with significant difference. In patients of the former two cohorts, better progression-free survival was significantly correlated with stage 0 or I, ductal carcinoma in situ or invasive ductal carcinoma, ≥71% estrogen receptor (ER) positivity, and the surgery extent reduction cohort than the other counterparts. Postoperative chemotherapy use was significantly correlated with lymph node metastasis, a high Ki67 labeling index, lymphovascular invasion, and a high Preoperative Endocrine Prognostic Index, at surgery after NET. Better recurrence-free survival after surgery was significantly correlated with high ER expression after NET and high PgR expression before and after NET.

CONCLUSIONS

NET can help to reduce the surgery extent or to avoid surgery in women with breast cancer of early-stage, ductal carcinoma, or high ER expression. NET may also contribute to appropriate decision of postoperative systemic therapy to improve survivals.

Hormone Receptor Expression on Endocrine Therapy in Patients with Breast Cancer: A Meta-Analysis

OBJECTIVE

To evaluate the role of hormone receptor expression on endocrine therapy in patients with breast cancer.

METHODS

The databases were used to collect the effect of high expression and low expression of hormone receptors on the efficacy of endocrine therapy in breast cancer. Two evaluators independently screened the literature based on preset inclusion and exclusion criteria. The quality of the article was evaluated using a modified Newcastle-Ottawa Scale (NOS) system. The survival data included in the literature were extracted and the ln(hazard ratio (HR)) and se[ln(HR)] of the overall survival (OS), disease-free survival (DFS), and recurrence-free survival (RFS) rates were calculated according to different level of hormone receptors. The RevMan 5.3 software was used to evaluate the meta-analysis.

RESULTS

A total of 13 relevant literature were included in the study. There were 8318 estrogen receptor (ER)-positive and 7926 progesterone receptor (PR)-positive patients. Overall survival, DFS, and RFS rates in high expression of ER(+) patients were significantly higher in low expression of ER(+) patients (OS HR = .59, 95% confidence interval (CI): .46-.76, P < .0001; DFS HR = .62, 95%CI: .50-.76, P < .00001; RFS HR = .44, 95% CI: .33-.58, P < .00001). In patients with high expression of PR(+), OS, DFS, and RFS rates were significantly higher than those with low expression of PR(+) (OS HR = .66, 95% CI: .57-.78, P < .00001; DFS HR = .52, 95% CI: .42-.65, P < .00001; RFS HR = .24, 95% CI: .11-.53, P = .0004).

CONCLUSION

The expression of ER and PR are powerful predictors of adjuvant endocrine therapy response. Breast cancer patients with high expression of hormone receptors benefit more from endocrine therapy and have better prognosis.

Neoadjuvant endocrine therapy in locally advanced estrogen or progesterone receptor-positive breast cancer: determining the optimal endocrine agent and treatment duration in postmenopausal women-a literature review and proposed guidelines

Introduction

For patients with locally advanced estrogen receptor or progesterone receptor-positive breast cancer, neoadjuvant endocrine therapy (NET) facilitates down-staging of the tumor and increased rates of breast-conserving surgery. However, NET remains under-utilized, and there are very limited clinical guidelines governing which therapeutic agent to use, or the optimal duration of treatment in postmenopausal women. This literature review aims to discuss the evidence surrounding (1) biomarkers for patient selection for NET, (2) the optimal neoadjuvant endocrine agent for postmenopausal women with locally advanced breast cancer, and (3) the optimal duration of NET. In addition, we make initial recommendations towards developing a clinical guideline for the prescribing of NET.

Method

A wide-ranging search of online electronic databases was conducted using a truncated PIC search strategy to identify articles that were relevant to these aims and revealed a number of key findings.

Results

Randomized trials have consistently demonstrated that aromatase inhibitors are more effective than tamoxifen, in terms of objective response rate and rate of BCS, and should be used as first-line NET. The three available aromatase inhibitors have so far been demonstrated to be biologically equivalent, with the choice of aromatase inhibitor not having been shown to affect clinical outcomes. There is increasing evidence for extending the duration of NET beyond 3 to 4 months, to at least 6 months or until maximal clinical response is achieved. While on-treatment levels of the proliferation marker Ki67 are predictive of long-term outcome, the choice of adjuvant therapy in patients who have received NET and then surgery is best guided by the preoperative endocrine prognostic index, or PEPI, which incorporates Ki67 with other clinical parameters.

Conclusion

This study reveals that in appropriately selected patients, NET can provide equivalent clinical benefit to neoadjuvant chemotherapy in the same cohort, if suitable treatments and durations are chosen. Our findings highlight the need for better defined biomarkers both for guiding patient selection and for measuring outcomes. Development of standard guidelines for the prescribing of NET has the potential to improve both clinical outcomes and quality of life in this patient cohort.

The pathological complete response and secreted protein acidic and rich in cysteine expression in patients with breast cancer receiving neoadjuvant nab-paclitaxel chemotherapy

Biomarkers that can accurately predict treatment response are required for indicating optimal neoadjuvant treatments. The current study assessed the predictive value of secreted protein acidic and rich in cysteine (SPARC) mRNA expression for the response to neoadjuvant nab-paclitaxel (nab-PTX) therapy in patients with breast cancer. It was hypothesized that SPARC expression can affect the response to albumin-bound taxanes, including nab-PTX since SPARC binds albumin with a high affinity. Pre-therapeutic specimens of core needle biopsies were analyzed from 50 patients in a phase II trial of neoadjuvant nab-PTX and the factors that were associated with a pathological complete response (pCR) were assessed. The pre-therapeutic tumor mRNA levels of chemotherapy-related proteins were quantified, including SPARC, and the correlations with post-therapeutic clinicopathological factors were assessed, including with pCR. The results demonstrated that pre-therapeutic SPARC mRNA expression was significantly higher in non-pCR patients compared with patients with pCR (92.37±55.33 vs. 56.53±30.19; P=0.027). A cutoff point of 48.5 was determined using receiver operating characteristic (ROC) curve analysis (sensitivity, 83.3%; specificity, 50.0%), and patients were classified into low and high SPARC expression groups. High SPARC expression was associated with histological grade (P=0.035), estrogen receptor expression (P=0.037), and progesterone receptor expression (P=0.002) but not with HER2 (P=0.895), and Ki-67 LI (P=0.743) expression. The results of the current study indicated that a high SPARC mRNA expression was a negative predictor of pCR following neoadjuvant nab-PTX therapy regardless of breast cancer subtype. The phase II study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Ethics Committee of the National Hospital Organization Takasaki General Medical Center (Registration nos. H23-9 and H23-33).

Meta-analysis of the impact of progesterone receptor status on oncological outcomes in oestrogen receptor-positive breast cancer

BACKGROUND

Assessment of the oestrogen receptor (ER) provides important prognostic information in breast cancer. The impact of progesterone receptor (PgR) status is less clear. Standardization of immunohistochemical analysis of these receptors has reduced interstudy heterogeneity. The aim of this meta-analysis was to evaluate the impact of PgR negativity on outcomes in ER-positive (ER+) breast cancer.

METHODS

This study was performed according to PRISMA and MOOSE guidelines. PubMed, Embase and the Cochrane Library were searched systematically to identify studies comparing disease-free survival as the primary outcome and overall survival as secondary outcome between PgR-positive (PgR+) and PgR-negative (PgR-) status in ER+ breast cancer. A meta-analysis of time-to-effect measures from included studies was undertaken.

RESULTS

Eight studies including 13 667 patients, 11 838 in the ER+PgR+ group and 1829 in the ER+PgR- group, met the inclusion criteria. Treatment characteristics did not differ significantly between the two groups. Patients in the ER+PgR- group had a higher risk of disease recurrence than those who had ER+PgR+ disease (hazard ratio (HR) 1·57, 95 per cent c.i. 1·38 to 1·79; P < 0·001). This hazard was increased in patients with human epidermal growth factor receptor 2-negative tumours (HR 1·62, 1·37 to 1·93; P < 0·001). A similar result was observed for overall survival (HR 1·69, 1·33 to 2·14; P < 0·001).

CONCLUSION

PgR negativity is associated with significant reductions in disease-free and overall survival in ER+ breast cancer. Treatment and surveillance strategies in these patients should be tailored accordingly.

Predictive and Prognostic Roles of Pathological Indicators for Patients with Breast Cancer on Neoadjuvant Chemotherapy

Currently, neoadjuvant chemotherapy is a standard therapeutic strategy for breast cancer, as it can provide timely and individualized chemo-sensitivity information and is beneficial for custom-designing subsequent treatment strategies. To accurately select candidates for neoadjuvant chemotherapy, the association between various immunohistochemical biomarkers of primary disease and tumor response to neoadjuvant chemotherapy has been investigated, and results have shown that certain pathological indicators evaluated after neoadjuvant chemotherapy are associated with long-term prognosis. The Food and Drug Administration (FDA) has recommended that complete pathological response can be used as a surrogate endpoint for neoadjuvant chemotherapy, which is related to better prognosis. Considering that residual tumor persists in the majority of patients after neoadjuvant chemotherapy, the value of various pathological indicators of residual disease in predicting the long-term outcomes is being extensively investigated. This review summarizes and compares various predictive and prognostic indicators for patients who have received neoadjuvant chemotherapy, and analyzes their efficacy in different breast cancer subtypes.

Utility of Ki67 labeling index, cyclin D1 expression, and ER-activity level in postmenopausal ER-positive and HER2-negative breast cancer with neoadjuvant chemo-endocrine therapy

In this study, we investigated the relationships of pathological response after neoadjuvant chemo-endocrine therapy with alterations in the Ki67 labeling index (LI), expression of cyclin D1 (CCND1) and progesterone receptor (PgR), and estrogen receptor (ER) activity in breast cancer. A total of 43 Japanese post-menopausal ER-positive and human epidermal growth factor receptor 2-negative invasive breast cancer patients with tumors >2 cm or positive lymph nodes were enrolled. Exemestane alone was administered for 2 months. Neoadjuvant chemo-endocrine therapy included four cycles of doxorubicin plus paclitaxel followed by weekly paclitaxel. The immunohistochemical expression of Ki67 LI, CCND1, and PgR, and ER activity were evaluated using core needle biopsy samples at the pretreatment and post-exemestane alone stages. ER activity was evaluated through transfection of an adenovirus vector carrying an estrogen-response element-green fluorescent protein gene. In current study, marked pathological responses (including 4.7% with pathological complete response) were obtained in 34.9% of patients. Ki67 LI and PgR expression were significantly decreased after treatment. High Ki67 LI at pretreatment was a significant predictive factor of marked pathological response. At the stage of post-exemestane alone, Ki67 LI was not significantly associated with pathological response; however, high CCND1 expression was significantly correlated with high Ki67 LI. Moreover, low-level ER activity at the post-exemestane alone stage was significantly associated with marked pathological response. In conclusions, pretreatment Ki67 LI was a predictor of response to neoadjuvant chemo-endocrine therapy. CCND1 expression and ER activity at the post-endocrine therapy alone stage may be useful in determining further treatments.

Progesterone Effects in the Nervous System

The sex hormone progesterone is mainly known as a key factor in establishing and maintaining pregnancy. In addition, progesterone has been shown to induce morphological changes in the central and peripheral nervous system by increasing dendrito-, spino-, and synaptogenesis in Purkinje cells (Wessel et al.: Cell Mol Life Sci (2014a) 1723-1740) and increasing axonal outgrowth in dorsal root ganglia (Olbrich et al.: Endocrinology (2013) 3784-3795). These effects mediated mainly by the classical progesterone receptors (PRs) A and B seem to be limited to young neurons. It may be assumed that microRNAs (miRNAs), which are potent regulators of nervous system maturation and degeneration, are also involved in the regulation of progesterone-mediated neuronal plasticity by altering the expression patterns of the corresponding PR A/B receptors (Theis and Theiss: Neural Regen Res (2015) 547-549, Pieczora et al.: Cerebellum (2017) 376-387). This review critically discusses current data on the neuroprotective effect of progesterone and its corresponding receptors in the nervous system, with possible regulatory processes by miRNAs. Preclinical studies on stroke and traumatic brain injury revealed neuroprotective and neuroregenerative effects of progesterone in the treatment of severe neurological diseases in animal models, but have so far failed in humans. In this context, the identification of specific miRNAs that regulate the expression of progesterone and PR could help to exploit the neuroprotective potential of progesterone for the treatment of various neurological disorders. Anat Rec, 302:1276-1286, 2019. © 2019 Wiley Periodicals, Inc.