Cytokeratin 5/6 fingerprinting in HER2-positive tumors identifies a poor prognosis and trastuzumab-resistant basal-HER2 subtype of breast cancer

Clinicopathological features of cytokeratin 5-positive pulmonary adenocarcinoma

Cytokeratin 5 (CK5) is a marker for pulmonary squamous cell carcinoma; however, CK5 is sometimes present in pulmonary adenocarcinoma (ADC), and there is insufficient information regarding the clinicopathological features of CK5-positive ADC. We aimed to explore the clinicopathological characteristics of CK5-positive ADC using immunohistochemistry. We prepared the following two cohorts: a resected cohort containing 220 resected tumours for primarily studying the detailed morphological characteristics, and a tissue microarray (TMA) cohort containing 337 samples for investigating the associations of CK5 expression with other protein expressions, genetic and prognostic findings. CK5-positive ADC was defined to have ≥ 10% tumour cells and presence of CK5-positive tumour cells in the resected and TMA cohorts, respectively. CK5-positive ADCs were identified in 91 (16.3%) patients in the combined cohort. CK5-positive ADCs had male predominance (P = 0.012), smoking history (P = 0.001), higher stage (P < 0.001), histological high-grade components (P < 0.001), vascular invasion (P < 0.001), mucinous differentiation (P < 0.001), spread through airspaces (P < 0.001), EGFR wild-type (P < 0.001), KRAS mutations (P < 0.001), ALK rearrangement (P < 0.001) and ROS1 rearrangement (P = 0.002). In the resected cohort, more than half the CK5-positive ADCs (19 cases, 65.5%) showed mucinous differentiation; the remaining cases harboured high-grade components. In the TMA cohort, CK5-positive ADCs correlated with TTF-1 negativity (P = 0.002) and MUC5B, MUC5AC and HNF4alpha positivity (P < 0.001, 0.048, < 0.001). Further, CK5-positive ADCs had significantly lower disease-free and overall survival rates than CK5-negative ADCs (P < 0.001 for each). Additionally, multivariate analysis revealed that CK5 expression was an independent poor prognostic factor. CK5-positive ADCs showed aggressive clinical behaviour, with high-grade morphology and mucinous differentiation.

Fatty acid synthase: A druggable driver of breast cancer brain metastasis

INTRODUCTION

Brain metastasis (BrM) is a key contributor to morbidity and mortality in breast cancer patients, especially among high-risk epidermal growth factor receptor 2-positive (HER2+) and triple-negative/basal-like molecular subtypes. Optimal management of BrM is focused on characterizing a "BrM dependency map" to prioritize targetable therapeutic vulnerabilities.

AREAS COVERED

We review recent studies addressing the targeting of BrM in the lipid-deprived brain environment, which selects for brain-tropic breast cancer cells capable of cell-autonomously generating fatty acids by upregulating de novo lipogenesis via fatty acid synthase (FASN). Disruption of FASN activity impairs breast cancer growth in the brain, but not extracranially, and mapping of the molecular causes of organ-specific patterns of metastasis has uncovered an enrichment of lipid metabolism signatures in brain metastasizing cells. Targeting SREBP1-the master regulator of lipogenic gene transcription-curtails the ability of breast cancer cells to survive in the brain microenvironment.

EXPERT OPINION

Targeting FASN represents a new therapeutic opportunity for patients with breast cancer and BrM. Delivery of brain-permeable FASN inhibitors and identifying strategies to target metabolic plasticity that might compensate for impaired brain FASN activity are two potential roadblocks that may hinder FASN-centered strategies against BrM.

A single-cell analysis of breast cancer cell lines to study tumour heterogeneity and drug response

Cancer cells within a tumour have heterogeneous phenotypes and exhibit dynamic plasticity. How to evaluate such heterogeneity and its impact on outcome and drug response is still unclear. Here, we transcriptionally profile 35,276 individual cells from 32 breast cancer cell lines to yield a single cell atlas. We find high degree of heterogeneity in the expression of biomarkers. We then train a deconvolution algorithm on the atlas to determine cell line composition from bulk gene expression profiles of tumour biopsies, thus enabling cell line-based patient stratification. Finally, we link results from large-scale in vitro drug screening in cell lines to the single cell data to computationally predict drug responses starting from single-cell profiles. We find that transcriptional heterogeneity enables cells with differential drug sensitivity to co-exist in the same population. Our work provides a framework to determine tumour heterogeneity in terms of cell line composition and drug response.

Poor histologic tumor response after adjuvant therapy in basal-like HER2-positive breast carcinoma

AIMS

HER2-positive breast carcinomas are all treated with first-line anti-HER2 therapy. However, immunohistochemical and molecular profiling demonstrates significant heterogeneity among HER2-positive carcinomas. Basal-like HER2-positive breast carcinomas are poorly differentiated from pure HER2-positive breast carcinomas.

MATERIALS AND METHODS

Seventy-five patients with HER2-positive, ER- and PR-negative breast carcinomas who received anti-HER2 based neoadjuvant therapy were retrospectively analyzed. Thirty-seven cases were classified as basal-like HER2-positive breast carcinoma with any positivity for CK5/6, and thirty-eight cases were classified as pure HER2-positive breast carcinoma with completely negativity for CK5/6. The clinicopathological features and tumor responses after neoadjuvant therapy and outcomes were analyzed.

RESULTS

Compared to non-basal HER2-positive breast carcinoma, basal-like HER2-positive breast carcinoma showed distinctive histologic features including poor differentiation and syncytial tumor cells with pushing, invasive borders and a significantly higher proportion of apocrine metaplasia. They also demonstrated significantly higher histologic grade; 18/37 (48.6%) of basal-like carcinomas were grade 3, whereas only 5/38 (13.2%) of non-basal carcinomas were grade 3 (p = 0.001), Furthermore, basal-like HER2-positive breast carcinomas were more likely to be positive or completely negative for p53 (p = 0.009), and demonstrated a higher percentage of TP53 mutation (p = 0.17). These tumors were less responsive to anti-HER2 based neoadjuvant therapy, with Miller-Payne grades 1-3 higher than pure HER2-positive breast carcinoma (25/37 [67.6%] vs 16/38 [42.1%]), and the percentage of grade 4-5 was lower (12/37 [32.4%] vs 22/38 [57.9%]; p = 0.027).

CONCLUSIONS

Basal-like HER2-positive breast carcinoma has distinctive clinicopathological features and less histologic tumor response after neoadjuvant therapy. There is urgent need to recognize basal-like HER2-positive breast carcinoma to be treated precisely.

ΔN63 suppresses the ability of pregnancy-identified mammary epithelial cells (PIMECs) to drive HER2-positive breast cancer

While pregnancy is known to reduce a woman's life-long risk of breast cancer, clinical data suggest that it can specifically promote HER2 (human EGF receptor 2)-positive breast cancer subtype (HER2+ BC). HER2+ BC, characterized by amplification of HER2, comprises about 20% of all sporadic breast cancers and is more aggressive than hormone receptor-positive breast cancer (the majority of cases). Consistently with human data, pregnancy strongly promotes HER2+ BC in genetic mouse models. One proposed mechanism of this is post-pregnancy accumulation of PIMECs (pregnancy-identified mammary epithelial cells), tumor-initiating cells for HER2+ BC in mice. We previously showed that p63, a homologue of the tumor suppressor p53, is required to maintain the post-pregnancy number of PIMECs and thereby promotes HER2+ BC. Here we set to test whether p63 also affects the intrinsic tumorigenic properties of PIMECs. To this end, we FACS-sorted YFP-labeled PIMECs from p63+/-;ErbB2 and control p63+/+;ErbB2 females and injected their equal amounts into immunodeficient recipients. To our surprise, p63+/- PIMECs showed increased, rather than decreased, tumorigenic capacity in vivo, i.e., significantly accelerated tumor onset and tumor growth, as well as increased self-renewal in mammosphere assays and proliferation in vitro and in vivo. The underlying mechanism of these phenotypes seems to be a specific reduction of the tumor suppressor TAp63 isoform in p63+/- luminal cells, including PIMECs, with concomitant aberrant upregulation of the oncogenic ΔNp63 isoform, as determined by qRT-PCR and scRNA-seq analyses. In addition, scRNA-seq revealed upregulation of several cancer-associated (Il-4/Il-13, Hsf1/HSP), oncogenic (TGFβ, NGF, FGF, MAPK) and self-renewal (Wnt, Notch) pathways in p63+/-;ErbB2 luminal cells and PIMECs per se. Altogether, these data reveal a complex role of p63 in PIMECs and pregnancy-associated HER2+ BC: maintaining the amount of PIMECs while suppressing their intrinsic tumorigenic capacity.

Genetic Variation and Immunohistochemical Localization of the Glucocorticoid Receptor in Breast Cancer Cases from the Breast Cancer Care in Chicago Cohort

BACKGROUND

Glucocorticoid, one of the primary mediators of stress, acts via its receptor, the glucocorticoid receptor (GCR/NR3C1), to regulate a myriad of physiological processes. We measured the genetic variation and protein expression of GCR, and the genes that regulate GCR function or response and examined whether these alterations were associated with breast cancer clinicopathological characteristics.

METHOD

We used samples from a multiracial cohort of breast cancer patients to assess the association between breast cancer characteristics and the genetic variants of single nucleotide polymorphisms (SNPs) in GCR/NR3C1, FKBP5, Sgk1, IL-6, ADIPOQ, LEPR, SOD2, CAT, and BCL2.

RESULTS

Several SNPs were associated with breast cancer characteristics, but statistical significance was lost after adjustment for multiple comparisons. GCR was detected in all normal breast tissues and was predominantly located in the nuclei of the myoepithelial cell layer, whereas the luminal layer was negative for GCR. GCR expression was significantly decreased in all breast cancer tissue types, compared to nontumor tissue, but was not associated with breast cancer characteristics. We found that high nuclear GCR expression was associated with basal cell marker cytokeratin 5/6 positivity.

CONCLUSION

GCR expression is reduced in breast cancer tissue and correlates with the basal cell marker CK5/6.

HER2 in stemness and epithelial-mesenchymal plasticity of breast cancer

Breast cancer had been the first non-hematologic malignancy where sub-types based on molecular characterization had entered clinical practice. HER2 over-expression, due to either gene amplification or protein up-regulation, defines one of these sub-types and is clinically exploited by addition of HER2-targeted treatments to the regimens of treatment. Nevertheless, in many occasions HER2-positive cancers are resistant or become refractory to these therapies. Several mechanisms, such as activation of alternative pathways or loss of expression of the receptor in cancer cells, have been proposed as the cause of these therapeutic failures. Cancer stem cells (CSCs, alternatively called tumor-initiating cells) comprise a small percentage of the tumor cells, but are capable of reconstituting and propagating tumors due to their superior intrinsic capacity for regeneration, survival and resistance to therapies. CSCs possess circuits enabling epigenetic plasticity which endow them with the ability to alternate between epithelial and mesenchymal states. This paper will discuss the expression and regulation of HER2 in CSCs of the different sub-types of breast cancer and relationships of the receptor with both the circuits of stemness and epithelial-mesenchymal plasticity. Therapeutic repercussions of the relationship of HER2-initiated signaling with stemness networks will also be proposed.

Effectiveness of neo-adjuvant systemic therapy with trastuzumab for basal HER2 type breast cancer: results from retrospective cohort study of Japan Breast Cancer Research Group (JBCRG)-C03

PURPOSE

While human epidermal growth factor receptor 2 (HER2) target therapies have significantly improved the prognosis of patients with HER2-enriched breast cancer, differing clinical benefits and gene expression analyses suggest a divergent HER2 subgroup. We aimed to investigate whether the basal HER2 subtype of breast cancer has distinguished characteristics.

METHODS

We performed a substudy by using data from a retrospective multi-institutional cohort of JBCRG-C03. Between 2001 and 2011, we identified 184 eligible patients who received concurrent neo-adjuvant chemotherapy (NAC) with trastuzumab for hormone receptor-negative and HER2-positive breast cancer. We defined basal HER2 subtype breast cancer as HER2-positive, ER/PgR-negative, and basal markers (EGFR, CK14 or CK5/6) positive by immunohistochemistrical evaluation. The pathologic complete response (pCR) and disease-free survival (DFS) rates were compared between the two subtypes.

RESULTS

A total of 127 (69.0%) patients achieved pCR after NAC and 29 (15.8%) patients experienced events of DFS within a 42 month median follow-up period (interquartile range 26-58 months). Although the basal HER2 subtype was related with poor DFS (3 year DFS: non-basal HER2, 95.0%; basal HER2, 86.9%; adjusted HR 3.4; 95% CI 1.2-14.5), neither the subtype (pCR: non-basal HER2, 75%; basal HER2, 66.7%; adjusted OR 0.60; 95% CI 0.27-1.28) nor the degree of expression of basal markers was significantly related with the pCR rate.

CONCLUSION

Basal HER2 phenotype showed poor DFS, but equivalent pCR rate after concurrent neo-adjuvant chemotherapy with trastuzumab. A different treatment approach to basal-HER2 type is needed even for cases that achieved adequate clinical response after NAC.

Reversible p53 inhibition prevents cisplatin ototoxicity without blocking chemotherapeutic efficacy

Cisplatin is a widely used chemotherapy drug, despite its significant ototoxic side effects. To date, the mechanism of cisplatin‐induced ototoxicity remains unclear, and hearing preservation during cisplatin‐based chemotherapy in patients is lacking. We found activation of the ATM‐Chk2‐p53 pathway to be a major determinant of cisplatin ototoxicity. However, prevention of cisplatin‐induced ototoxicity is hampered by opposite effects of ATM activation upon sensory hair cells: promoting both outer hair cell death and inner hair cell survival. Encouragingly, however, genetic or pharmacological ablation of p53 substantially attenuated cochlear cell apoptosis, thus preserving hearing. Importantly, systemic administration of a p53 inhibitor in mice bearing patient‐derived triple‐negative breast cancer protected auditory function, without compromising the anti‐tumor efficacy of cisplatin. Altogether, these findings highlight a novel and effective strategy for hearing protection in cisplatin‐based chemotherapy.

Keratin 5 overexpression is associated with serous ovarian cancer recurrence and chemotherapy resistance

This study investigated the clinical significance of keratin 5 and 6 expression in serous ovarian cancer progression and chemotherapy resistance. KRT5 and KRT6 (KRT6A, KRT6B & KRT6C) gene expression was assessed in publically available serous ovarian cancer data sets, ovarian cancer cell lines and primary serous ovarian cancer cells. Monoclonal antibodies which detect both K5/6 or only K5 were used to assess protein expression in ovarian cancer cell lines and a cohort of high grade serous ovarian carcinomas at surgery (n = 117) and after neoadjuvant chemotherapy (n = 21). Survival analyses showed that high KRT5 mRNA in stage III/IV serous ovarian cancers was significantly associated with reduced progression-free (HR 1.38, P < 0.0001) and overall survival (HR 1.28, P = 0.013) whilst high KRT6 mRNA was only associated with reduced progression-free survival (HR 1.2, P = 0.031). Both high K5/6 (≥ 10%, HR 1.78 95% CI; 1.03−2.65, P = 0.017) and high K5 (≥ 10%, HR 1.90, 95% CI; 1.12−3.19, P = 0.017) were associated with an increased risk of disease recurrence. KRT5 but not KRT6C mRNA expression was increased in chemotherapy resistant primary serous ovarian cancer cells compared to chemotherapy sensitive cells. The proportion of serous ovarian carcinomas with high K5/6 or high K5 immunostaining was significantly increased following neoadjuvant chemotherapy. K5 can be used to predict serous ovarian cancer prognosis and identify cancer cells that are resistant to chemotherapy. Developing strategies to target K5 may therefore improve serous ovarian cancer survival.

Cancer stem cell-driven efficacy of trastuzumab (Herceptin): towards a reclassification of clinically HER2-positive breast carcinomas

Clinically HER2+ (cHER2+) breast cancer (BC) can no longer be considered a single BC disease entity in terms of trastuzumab responsiveness. Here we propose a framework for predicting the response of cHER2+ to trastuzumab that integrates the molecular distinctions of intrinsic BC subtypes with recent knowledge on cancer stem cell (CSC) biology. First, we consider that two interchangeable populations of epithelial-like, aldehyde dehydrogenase (ALDH)-expressing and mesenchymal-like, CD44+CD24-/low CSCs can be found in significantly different proportions across all intrinsic BC subtypes. Second, we overlap all the intrinsic subtypes across cHER2+ BC to obtain a continuum of mixed phenotypes in which one extreme exhibits a high identity with ALDH+ CSCs and the other extreme exhibits a high preponderance of CD44+CD24-/low CSCs. The differential enrichment of trastuzumab-responsive ALDH+ CSCs versus trastuzumab-refractory CD44+CD24-/low CSCs can explain both the clinical behavior and the primary efficacy of trastuzumab in each molecular subtype of cHER2+ (i.e., HER2-enriched/cHER2+, luminal A/cHER2+, luminal B/cHER2+, basal/cHER2+, and claudin-low/cHER2+). The intrinsic plasticity determining the epigenetic ability of cHER2+ tumors to switch between epithelial and mesenchymal CSC states will vary across the continuum of mixed phenotypes, thus dictating their intratumoral heterogeneity and, hence, their evolutionary response to trastuzumab. Because CD44+CD24-/low mesenchymal-like CSCs distinctively possess a highly endocytic activity, the otherwise irrelevant HER2 can open the door to a type of "Trojan horse" approach by employing antibody-drug conjugates such as T-DM1, which will allow a rapid and CSC-targeted delivery of cytotoxic drugs to therapeutically manage trastuzumab-unresponsive basal/cHER2+ BC. Contrary to the current dichotomous model used clinically, our model proposes that a reclassification of cHER2+ tumors based on the spectrum of molecular BC subtypes might inform on their CSC-determined sensitivity to trastuzumab, thus providing a better delineation of the predictive value of cHER2+ in BC by incorporating CSCs-driven intra-tumor heterogeneity into clinical decisions.