FOXC1 and SOX10 in Estrogen Receptor-Low Positive/HER2-Negative Breast Cancer: Potential Biomarkers for the Basal-like Phenotype Prediction

CONTEXT.—

Breast cancer with low (1%-10%) estrogen receptor (ER) expression (ER-low positive) constitutes a small portion of invasive breast cancers, and the treatment strategy for these tumors remains debatable.

OBJECTIVE.—

To characterize the features and outcomes of ER-low positive patients, and clarify the clinical significance of FOXC1 and SOX10 expression in ER-low positive/HER2-negative tumors.

DESIGN.—

Among 9082 patients diagnosed with primary invasive breast cancer, the clinicopathologic features of those with ER-low positive breast cancer were characterized. FOXC1 and SOX10 mRNA levels were analyzed in ER-low positive/HER2-negative cases from public data sets. The expression of FOXC1 and SOX10 in ER-low positive/HER2-negative tumors was evaluated by immunohistochemistry.

RESULTS.—

The clinicopathologic study of ER-low positive tumors indicated more aggressive characteristics compared with those tumors with ER >10%, while they had more overlapping features with ER-negative tumors irrespective of the HER2 status. The intrinsic molecular subtype of ER-low positive cases with high FOXC1 and SOX10 mRNA expression was more likely to be nonluminal. Among the ER-low positive/HER2-negative tumors, 56.67% (51 of 90) and 36.67% (33 of 90) were positive for FOXC1 and SOX10, respectively, which was significantly positively correlated with CK5/6 expression. In addition, the survival analysis demonstrated no significant difference between patients who received and who did not receive endocrine therapy.

CONCLUSIONS.—

ER-low positive breast cancers biologically overlap more with ER-negative tumors. ER-low positive/HER2-negative cases demonstrate a high rate of FOXC1 or SOX10 expression, and these cases might be better categorized as a basal-like phenotype/subtype. FOXC1 and SOX10 testing may be used for the intrinsic phenotype prediction for ER-low positive/HER2-negative patients.

The Clinical and Biological Significance of Estrogen Receptor-Low Positive Breast Cancer

Estrogen receptor (ER) status in breast cancer (BC) is determined using immunohistochemistry (IHC) with nuclear expression in ≥1% of cells defined as ER-positive. BC with 1%-9% expression (ER-low-positive), is a clinically and biologically unique subgroup. In this study, we hypothesized that ER-low-positive BC represents a heterogeneous group with a mixture of ER-positive and ER-negative tumor, which may explain their divergent clinical behavior. A large BC cohort (n = 8171) was investigated and categorized into 3 groups: ER-low-positive (1%-9%), ER-positive (≥10%), and ER-negative (<1%) where clinicopathological and outcome characteristics were compared. A subset of ER-low-positive cases was further evaluated using IHC, RNAscope, and RT-qPCR. PAM50 subtyping and ESR1 mRNA expression levels were assessed in ER-low-positive cases within The Cancer Genome Atlas data set. The reliability of image analysis software in assessment of ER expression in the ER-low-positive category was also assessed. ER-low-positive tumors constituted <2% of BC cases examined and showed significant clinicopathological similarity to ER-negative tumors. Most of these tumors were nonluminal types showing low ESR1 mRNA expression. Further validation of ER status revealed that 45% of these tumors were ER-negative with repeated IHC staining and confirmed by RNAscope and RT-qPCR. ER-low-positive tumors diagnosed on needle core biopsy were enriched with false-positive ER staining. BCs with 10% ER behaved similar to ER-positive, rather than ER-negative or low-positive BCs. Moderate concordance was found in assessment of ER-low-positive tumors, and this was not improved by image analysis. Routinely diagnosed ER-low-positive BC includes a proportion of ER-negative cases. We recommend repeat testing of BC showing 1%-9% ER expression and using a cutoff ≥10% expression to define ER positivity to help better inform treatment decisions.

Evaluation oncotype DX® 21-gene recurrence score and clinicopathological parameters: a single institutional experience

AIMS

Oncotype DX recurrence score (RS) is a clinically validated assay, which predicts the likelihood of disease recurrence in oestrogen receptor-positive/HER2-negative (ER+/HER2-) breast cancer (BC). In this study we aimed to compare the performance of Oncotype DX against the conventional clinicopathological parameters using a large BC cohort diagnosed in a single institution.

METHODS AND RESULTS

A cohort (n = 430) of ER+/HER2- BC patients who were diagnosed at the Nottingham University Hospitals NHS Trust and had Oncotype DX testing was included. Correlation with the clinicopathological and other biomarkers, including the proliferation index, was analysed. The median Oncotype DX RS was 17.5 (range = 0-69). There was a significant association between high RS and grade 3 tumours. No grade 1 BC or grade 2 tumours with mitosis score 1 showed high RS. Low RS was significantly associated with special tumour types where none of the patients with classical lobular or tubular carcinomas had a high RS. There was an inverse association between RS and levels of ER and progesterone receptor (PR) expression and a positive linear correlation with Ki67 labelling index. Notably, six patients who developed recurrence had an intermediate RS; however, four of these six cases (67%) were identified as high-risk disease when the conventional clinical and molecular parameters were considered.

CONCLUSION

Oncotype DX RS is correlated strongly with the conventional clinicopathological parameters in BC. Some tumour features such as tumour grade, type, PR status and Ki67 index can be used as surrogate markers in certain scenarios.

Identifying Methylation Pattern and Genes Associated with Breast Cancer Subtypes

Breast cancer is regarded worldwide as a severe human disease. Various genetic variations, including hereditary and somatic mutations, contribute to the initiation and progression of this disease. The diagnostic parameters of breast cancer are not limited to the conventional protein content and can include newly discovered genetic variants and even genetic modification patterns such as methylation and microRNA. In addition, breast cancer detection extends to detailed breast cancer stratifications to provide subtype-specific indications for further personalized treatment. One genome-wide expression–methylation quantitative trait loci analysis confirmed that different breast cancer subtypes have various methylation patterns. However, recognizing clinically applied (methylation) biomarkers is difficult due to the large number of differentially methylated genes. In this study, we attempted to re-screen a small group of functional biomarkers for the identification and distinction of different breast cancer subtypes with advanced machine learning methods. The findings may contribute to biomarker identification for different breast cancer subtypes and provide a new perspective for differential pathogenesis in breast cancer subtypes.

Estrogen receptor variants in ER-positive basal-type breast cancers responding to therapy like ER-negative breast cancers

Immunohistochemically ER-positive HER2-negative (ER+HER2−) breast cancers are classified clinically as Luminal-type. We showed previously that molecular subtyping using the 80-gene signature (80-GS) reclassified a subset of ER+HER2− tumors to molecular Basal-type. We report here that molecular reclassification is associated with expression of dominant-negative ER variants and evaluate response to neoadjuvant therapy and outcome in the prospective neoadjuvant NBRST study (NCT01479101). The 80-GS reclassified 91 of 694 (13.1%) immunohistochemically Luminal-type tumors to molecular Basal-type. Importantly, all 91 discordant tumors were classified as high-risk, whereas only 66.9% of ER+/Luminal-type tumors were classified at high-risk for disease recurrence (i.e., Luminal B) (P < 0.001). ER variant mRNA (ER∆3, ER∆7, and ERα-36) analysis performed on 84 ER+/Basal tumors and 48 ER+/Luminal B control tumors revealed that total ER mRNA was significantly lower in ER+/Basal tumors. The relative expression of ER∆7/total ER was significantly higher in ER+/Basal tumors compared to ER+/Luminal B tumors (P < 0.001). ER+/Basal patients had similar pathological complete response (pCR) rates following neoadjuvant chemotherapy as ER−/Basal patients (34.3 vs. 37.6%), and much higher than ER+/Luminal A or B patients (2.3 and 5.8%, respectively). Furthermore, 3-year distant metastasis-free interval (DMFI) for ER+/Basal patients was 65.8%, significantly lower than 96.3 and 88.9% for ER+/Luminal A and B patients, respectively, (log-rank P < 0.001). Significantly lower total ER mRNA and increased relative ER∆7 dominant-negative variant expression provides a rationale why ER+/Basal breast cancers are molecularly ER-negative. Identification of this substantial subset of patients is clinically relevant because of the higher pCR rate to neoadjuvant chemotherapy and correlation with clinical outcome.

Further evidence to support bimodality of oestrogen receptor expression in breast cancer

AIMS

Although oestrogen receptor (ER)-negative breast cancers (BCs) do not respond to hormone therapy, the response of ER-positive BCs is reported to be variable, which may suggest a dose-dependent effect. The aim of this study was to assess the pattern of ER expression in BCs at the protein (immunohistochemistry) and transcriptome (microarray-based gene expression) levels.

METHODS AND RESULTS

ER immunohistochemical (IHC) expression was assessed in a large series of BCs, including 3649 core biopsies and 1892 cases prepared as tissue microarrays (TMAs) stained with specific antibodies. ESR1 mRNA expression was assessed in the METABRIC study (1980 cases), by the use of the Linear Models for Microarray Data (limma) software, and the results were compared with protein levels. IHC data confirmed the bimodality of ER expression, with 92.2% and 89.2% of the cases showing completely negative (<1%) or highly positive (≥70%) expression on the cores and TMAs, respectively. Weakly positive cases (1-10%) and intermediately positive (11-69%) cases were infrequent (2.7% and 5.1%, and 1.6% and 9.2%, in cores and TMAs, respectively), and did not show survival difference from ER-negative tumours. When full-face sections of the corresponding excision specimens were immunostained, 47% of the ER-low/intermediate group were deemed to be ER-negative. Transcriptomic data not only showed a significant correlation between ESR1 mRNA and protein expression levels, but also confirmed the bimodality of ER expression at the mRNA level.

CONCLUSIONS

Our study provides further evidence that ER expression is bimodal, and that it is observed at both the mRNA and protein levels. The reported poor survival of BC patients with low ER expression in the early clinical trials may be related to the inclusion of ER-negative cases.