The concept of cancer cells being hierarchically organized and arising from their own progenitor stem cells will have important implications on cancer therapy. If this hypothesis were to be true then the paucity of estrogen receptors in stem cells as well as their inherent drug resistance mechanisms pose a challenge to current targeted therapies. In this study, we sought to examine the prognostic relevance of ALDH1, a putative cancer stem cell marker, by immunohistochemistry. The four cohorts analyzed included an adjuvantly treated series of 245 invasive cancers, a neoadjuvantly treated series of 34 cases, and two series of 58 and 40 triple negative cases, respectively. Both tumor cell and stromal expression for ALDH1 was evaluated, where possible. Tumor cell ALDH1 expression significantly correlated only with basal-like and HER2 tumor types in the adjuvant series and tumor grade in the neoadjuvant cohort. No significant enrichment for ALDH1 positive cells was observed in the postneoadjuvant therapy specimens compared to pretreatment samples. On the other hand, high degree of stromal expression was significantly associated with best disease-free survival as well as a trend for overall survival. The association of stromal expression was confirmed in an independent cohort of triple negative cases. The novel finding is that tumor microenvironment may play a significant role in determining the prognostic impact of stem/progenitor cells in human breast tumors.

Forkhead box protein A1 (FOXA1) is a "pioneer factor" that plays a role in controlling nearly 50% of estrogen receptor target genes. FOXA1 expression correlates with estrogen receptor (ER)-positivity especially in luminal subtype A breast cancers. The aim of this study was to investigate the precise role of FOXA1 in breast cancer using a large population-based cohort. Nuclear expression of FOXA1 was analyzed in a tissue microarray of 4,444 invasive breast cancer cases using immunohistochemistry and correlated with clinicopathologic variables using previously described methods and cutoff points. The entire cohort was equally divided into a training and validation set. All survival analyses were performed using a previously defined cutoff (3) for validation. Additional X-tile analysis performed to analyze prognostic effects of low and high FOXA1 levels identified 24 as a cutoff. Bonferroni-Holmes test was used as appropriate. FOXA1 expression significantly correlated positively with markers of good prognosis or ER-positivity, and negatively with tumor size, tumor grade, nodal status, Ki67, HER2 expression, and basal subtype (each P value <0.0001). In both survival analyses, FOXA1 was a significant predictor of breast cancer-specific survival (P < 0.0001) and relapse-free survival (P < 0.0001). FOXA1 was also an independent predictor of breast cancer-specific survival at 10 years using both cutoffs. Among the ER-positive subgroup treated with tamoxifen, FOXA1 was an independent prognostic marker using the 24 cutoff (P = 0.030). FOXA1 is a significant marker of good prognosis in breast cancer; it also identifies a subset of ER-positive tamoxifen treated patients at low risk of recurrence.

Metastasis in breast cancer carries a disproportionately worse prognosis than localized primary disease. To identify microRNAs (miRNA) involved in metastasis, the expression of 254 miRNAs was measured across the following cell lines using microarray analysis: MDA-MB-231 breast cancer cells, cells that grew as a tumor in the mammary fat pad of nude mice (TMD-231), metastatic disease to the lungs (LMD-231), bone (BMD-231) and adrenal gland (ADMD-231). A brain-seeking variant of this cell line (231-BR) was used additionally in validation studies. Twenty miRNAs were upregulated and seven were downregulated in metastatic cancer cells compared with TMD-231 cells. The expression of the tumor suppressor miRNAs let-7 and miR-22 was consistently downregulated in metastatic cancer cells. These metastatic cells expressed higher levels of putative/proven miR-22 target oncogenes ERBB3, CDC25C and EVI-1. Introduction of miR-22 into cancer cells reduced the levels of ERBB3 and EVI-1 as well as phospho-AKT, an EVI-1 downstream target. The miR-22 primary transcript is located in the 5 0 -untranslated region of an open reading frame C17orf91, and the promoter/enhancer of C17orf91 drives miR-22 expression. We observed elevated C17orf91 expression in non-basal subtype compared with basal subtype breast cancers. In contrast, elevated expression of EVI-1 was observed in basal subtype and was associated with poor outcome in estrogen receptor-negative breast cancer patients. These results suggest that metastatic cancer cells increase specific oncogenic signaling proteins through downregulation of miRNAs. Identifying such metastasisspecific oncogenic pathways may help to manipulate tumor behavior and aid in the design of more effective targeted therapies.

SummaryAurora A kinase is overexpressed in the majority of breast carcinomas. A chemical genetic approach was used to identify the malignant targets of Aurora A, which revealed pleckstrin-homology-like domain protein PHLDA1 as an Aurora A substrate. PHLDA1 downregulation is a powerful prognostic predictor for breast carcinoma, which was confirmed in our study. We further show that downregulation of PHLDA1 is associated with estrogen receptor (ER) expression in breast carcinoma. Aurora A directly phosphorylates PHLDA1 leading to its degradation. PHLDA1 also negatively regulates Aurora A, thereby triggering a feedback loop. We demonstrate the underlying mechanisms by which PHLDA1 upregulation strongly antagonizes Aurora-A-mediated oncogenic pathways, thereby revealing PHLDA1 degradation as a key mechanism by which Aurora A promotes breast malignancy. Thus, not surprisingly, PHLDA1 upregulation acts synergistically with Aurora A inhibition in promoting cell death. PHLDA1 overexpression might therefore be an alternative method to modulate Aurora A deregulation in breast carcinoma. Finally, this study led to the discovery of a mutation in the Aurora A active site that renders it amenable to the chemical genetic approach. Similar mutations are required for Aurora B, suggesting that this modified approach can be extended to other kinases that have hitherto not been amenable to this methodology.

Interobserver reproducibility in the diagnosis of benign intraductal proliferative lesions has been poor. The aims of the study were to investigate the inter-and intraobserver variability and the impact of the addition of an immunostain for high-and low-molecular weight keratins on the variability. Nine pathologists reviewed 81 cases of breast proliferative lesions in three stages and assigned each of the lesions to one of the following three diagnoses: usual ductal hyperplasia, atypical ductal hyperplasia and ductal carcinoma in situ. Hematoxylin and eosin slides and corresponding slides stained with ADH-5 cocktail (cytokeratins (CK) 5, 14. 7, 18 and p63) by immunohistochemistry were evaluated. Concordance was evaluated at each stage of the study. The interobserver agreement among the nine pathologists for diagnosing the 81 proliferative breast lesions was fair (j-value ¼ 0.34). The intraobserver j-value ranged from 0.56 to 0.88 (moderate to strong). Complete agreement among nine pathologists was achieved in only nine (11%) cases, at least eight agreed in 20 (25%) cases and seven or more agreed in 38 (47%) cases. Following immunohistochemical stain, a significant improvement in the interobserver concordance (overall j-value ¼ 0.50) was observed (P ¼ 0.015). There was a significant reduction in the total number of atypical ductal hyperplasia diagnosis made by nine pathologists after the use of ADH-5 immunostain. Atypical ductal hyperplasia still remains a diagnostic dilemma with wide variation in both inter-and intraobserver reproducibility among pathologists. The addition of an immunohistochemical stain led to a significant improvement in the concordance rate. More importantly, there was an 8% decrease in the number of lesions classified as atypical ductal hyperplasia in favor of usual hyperplasia; in clinical practice, this could lead to a decrease in the number of surgeries carried out for intraductal proliferative lesions.