Chemokine receptors and their ligands in breast cancer: The key roles in progression and metastasis

Chemokines and their receptors are a family of chemotactic cytokines with important functions in the immune response in both health and disease. Their known physiological roles such as the regulation of leukocyte trafficking and the development of immune organs generated great interest when it was found that they were also related to the control of early and late inflammatory stages in the tumor microenvironment. In fact, in breast cancer, an imbalance in the synthesis of chemokines and/or in the expression of their receptors was attributed to be involved in the regulation of disease progression, including invasion and metastasis. Research in this area is progressing rapidly and the development of new agents based on chemokine and chemokine receptor antagonists are emerging as attractive alternative strategies. This chapter provides a snapshot of the different functions reported for chemokines and their receptors with respect to the potential to regulate breast cancer progression.

Defining the relevance of surgical margins. Part two: Strategies to improve prediction of recurrence risk

Due to the complex nature of tumour biology and the integration between host tissues and molecular processes of the tumour cells, a continued reliance on the status of the microscopic cellular margin should not remain our only determinant of the success of a curative-intent surgery for patients with cancer. Based on current evidence, relying on a purely cellular focus to provide a binary indication of treatment success can provide an incomplete interpretation of potential outcome. A more holistic analysis of the cancer margin may be required. If we are to move ahead from our current situation - and allow treatment plans to be more intelligently tailored to meet the requirements of each individual tumour - we need to improve our utilisation of techniques that either improve recognition of residual tumour cells within the surgical field or enable a more comprehensive interrogation of tumour biology that identifies a risk of recurrence. In the second article in this series on defining the relevance of surgical margins, the authors discuss possible alternative strategies for margin assessment and evaluation in the canine and feline cancer patient. These strategies include considering adoption of the residual tumour classification scheme; intra-operative imaging systems including fluorescence-guided surgery, optical coherence tomography and Raman spectroscopy; molecular analysis and whole transcriptome analysis of tissues; and the development of a biologic index (nomogram). These techniques may allow evaluation of individual tumour biology and the status of the resection margin in ways that are different to our current techniques. Ultimately, these techniques seek to better define the risk of tumour recurrence following surgery and provide the surgeon and patient with more confidence in margin assessment.

Concurrent DNA Copy-Number Alterations and Mutations in Genes Related to Maintenance of Genome Stability in Uninvolved Mammary Glandular Tissue from Breast Cancer Patients

Somatic mosaicism for DNA copy-number alterations (SMC-CNAs) is defined as gain or loss of chromosomal segments in somatic cells within a single organism. As cells harboring SMC-CNAs can undergo clonal expansion, it has been proposed that SMC-CNAs may contribute to the predisposition of these cells to genetic disease including cancer. Herein, the gross genomic alterations (>500 kbp) were characterized in uninvolved mammary glandular tissue from 59 breast cancer patients and matched samples of primary tumors and lymph node metastases. Array-based comparative genomic hybridization showed 10% (6/59) of patients harbored one to 359 large SMC-CNAs (mean: 1,328 kbp; median: 961 kbp) in a substantial portion of glandular tissue cells, distal from the primary tumor site. SMC-CNAs were partially recurrent in tumors, albeit with considerable contribution of stochastic SMC-CNAs indicating genomic destabilization. Targeted resequencing of 301 known predisposition and somatic driver loci revealed mutations and rare variants in genes related to maintenance of genomic integrity: BRCA1 (p.Gln1756Profs*74, p.Arg504Cys), BRCA2 (p.Asn3124Ile), NCOR1 (p.Pro1570Glnfs*45), PALB2 (p.Ser500Pro), and TP53 (p.Arg306*). Co-occurrence of gross SMC-CNAs along with point mutations or rare variants in genes responsible for safeguarding genomic integrity highlights the temporal and spatial neoplastic potential of uninvolved glandular tissue in breast cancer patients.

Molecular Heterogeneity in Primary Breast Carcinomas and Axillary Lymph Node Metastases Assessed by Genomic Fingerprinting Analysis

Molecular heterogeneity within primary breast carcinomas and among axillary lymph node (LN) metastases may impact diagnosis and confound treatment. In this study, we used short tandem repeated sequences to assess genomic heterogeneity and to determine hereditary relationships among primary tumor areas and regional metastases from 30 breast cancer patients. We found that primary carcinomas were genetically heterogeneous and sampling multiple areas was necessary to adequately assess genomic variability. LN metastases appeared to originate at different time periods during disease progression from different sites of the primary tumor and the extent of genomic divergence among regional metastases was associated with a less favorable patient outcome (P = 0.009). In conclusion, metastasis is a complex process influenced by primary tumor heterogeneity and variability in the timing of dissemination. Genomic variation in primary breast tumors and regional metastases may negatively impact clinical diagnostics and contribute to therapeutic resistance.

Genomic (in)stability of the breast tumor microenvironment

The breast tumor microenvironment plays an active role in tumorigenesis. Molecular alterations have been identified in tumor-associated stroma; however, there is considerable debate as to whether the stroma is characterized by genomic instability or whether detection of chromosomal alterations reflects technological artifact rather than the true genomic content of the tumor microenvironment. Thus, breast stroma specimens from 112 women undergoing reductive mammoplasty (n = 7), prophylactic mastectomy (n = 6), or mastectomy for a breast disease (n = 99) were frozen in optimal cutting temperature medium. Allelic imbalance (AI) analysis was conducted using a panel of 52 microsatellite markers in 484 stromal specimens from 98 women, of which 92% had no detectable AI events. When compared with previously generated AI data from 77 formalin-fixed, paraffin-embedded (FFPE) stroma specimens, 42% of which harbored at least one detectable AI event, the frequency of AI in the FFPE specimens (4.62%) was significantly higher (P < 0.001) than that found in frozen specimens (0.45%). This comparison of AI between FFPE and research-grade specimens suggests that past reports of AI in breast stroma reflect artifact in the archival specimens caused by formalin-fixation, paraffin-embedding and tissue storage. Furthermore, SNP data were generated from a subset of 86 stromal specimens using SNP arrays and copy number alterations were identified using Partek Genomics Suite. For 95% of the specimens, no detectable copy number alterations were found and the 11 changes that were detected were small and not shared between specimens. These data, therefore, support a model in which the tumor microenvironment is genetically stable.

Interactions between tumor cells and microenvironment in breast cancer: a new opportunity for targeted therapy

Breast cancer remains the leading cause of morbidity and second-leading cause of death in women. Despite efforts to uncover new targeted therapies, a vast number of women die due to refractory or recurrent breast tumors. Most breast cancer studies have focused on the intrinsic characteristics of breast tumor cells, including altered growth, proliferation, and metabolism. However, emerging research suggests that the tumor microenvironment can substantially affect relapse rates and therapeutic responses. In this review, we discuss the interactions between the tumor and microenvironment in breast cancer, with regard to mutational profiles and altered metabolism that could serve as potential therapeutic targets. We also describe current technologies available to study these interactions.

Understanding the "lethal" drivers of tumor-stroma co-evolution: emerging role(s) for hypoxia, oxidative stress and autophagy/mitophagy in the tumor micro-environment

We have recently proposed a new model for understanding how tumors evolve. To achieve successful "Tumor-Stroma Co-Evolution", cancer cells induce oxidative stress in adjacent fibroblasts and possibly other stromal cells. Oxidative stress in the tumor stroma mimics the effects of hypoxia, under aerobic conditions, resulting in an excess production of reactive oxygen species (ROS). Excess stromal production of ROS drives the onset of an anti-oxidant defense in adjacent cancer cells, protecting them from apoptosis. Moreover, excess stromal ROS production has a "Bystander-Effect", leading to DNA damage and aneuploidy in adjacent cancer cells, both hallmarks of genomic instability. Finally, ROS-driven oxidative stress induces autophagy and mitophagy in the tumor micro-environment, leading to the stromal over-production of recycled nutrients (including energy-rich metabolites, such as ketones and L-lactate). These recycled nutrients or chemical building blocks then help drive mitochondrial biogenesis in cancer cells, thereby promoting the anabolic growth of cancer cells (via an energy imbalance). We also show that ketones and lactate help "fuel" tumor growth and cancer cell metastasis and can act as chemo-attractants for cancer cells. We have termed this new paradigm for accelerating tumor-stroma co-evolution, "The Autophagic Tumor Stroma Model of Cancer Cell Metabolism". Heterotypic signaling in cancer-associated fibroblasts activates the transcription factors HIF1alpha and NFκB, potentiating the onset of hypoxic and inflammatory response(s), which further upregulates the autophagic program in the stromal compartment. Via stromal autophagy, this hypoxic/inflammatory response may provide a new escape mechanism for cancer cells during anti-angiogenic therapy, further exacerbating tumor recurrence and metastasis.

Horizontal gene transfer: you are what you eat

Horizontal or lateral gene transfer is an effective mechanism for the exchange of genetic information in bacteria allowing bacterial diversification and facilitating adaptation to new environments. Recent data demonstrate that DNA may also be transferred between somatic cells via the uptake of apoptotic bodies. This process allows transfer of viral genes that have been incorporated into the genome in a receptor-independent fashion. Transferred DNA is replicated and propagated in daughter cells in cell that have an inactivated DNA response which may impact tumor progression.

Breast cancer precursors revisited: molecular features and progression pathways

Increasingly more coherent data on the molecular characteristics of benign breast lesions and breast cancer precursors have led to the delineation of new multistep pathways of breast cancer progression through genotypic-phenotypic correlations. It has become apparent that oestrogen receptor (ER)-positive and -negative breast lesions are fundamentally distinct diseases. Within the ER-positive group, histological grade is strongly associated with the number and complexity of genetic abnormalities in breast cancer cells. Genomic analyses of high-grade ER-positive breast cancers have revealed that a substantial proportion of these tumours harbour the characteristic genetic aberrations found in low-grade ER-positive disease, suggesting that at least a subgroup of high-grade ER-positive breast cancers may originate from low-grade lesions. The ER-negative group is more complex and heterogeneous, comprising distinct molecular entities, including basal-like, HER2 and molecular apocrine lesions. Importantly, the type and pattern of genetic aberrations found in ER-negative cancers differ from those of ER-positive disease. Here, we review the available molecular data on breast cancer risk indicator and precursor lesions, the putative mechanisms of progression from in situ to invasive disease, and propose a revised model of breast cancer evolution based on the molecular characteristics of distinct subtypes of in situ and invasive breast cancers.