Breast cancer is a leading cause of death among women worldwide. Dysbiosis, an aberrant composition of the microbiome, characterizes breast cancer. In this review we discuss the changes to the metabolism of breast cancer cells, as well as the composition of the breast and gut microbiome in breast cancer. The role of the breast microbiome in breast cancer is unresolved, nevertheless it seems that the gut microbiome does have a role in the pathology of the disease. The gut microbiome secretes bioactive metabolites (reactivated estrogens, short chain fatty acids, amino acid metabolites, or secondary bile acids) that modulate breast cancer. We highlight the bacterial species or taxonomical units that generate these metabolites, we show their mode of action, and discuss how the metabolites affect mitochondrial metabolism and other molecular events in breast cancer. These metabolites resemble human hormones, as they are produced in a “gland” (in this case, the microbiome) and they are subsequently transferred to distant sites of action through the circulation. These metabolites appear to be important constituents of the tumor microenvironment. Finally, we discuss how bacterial dysbiosis interferes with breast cancer treatment through interfering with chemotherapeutic drug metabolism and availability.

Oncobiotic transformation of the gut microbiome may contribute to the risk of breast cancer. Recent studies have provided evidence that the microbiome secretes cytostatic metabolites that inhibit the proliferation, movement, and metastasis formation of cancer cells. In this study, we show that indolepropionic acid (IPA), a bacterial tryptophan metabolite, has cytostatic properties. IPA selectively targeted breast cancer cells, but it had no effects on non-transformed, primary fibroblasts. In cell-based and animal experiments, we showed that IPA supplementation reduced the proportions of cancer stem cells and the proliferation, movement, and metastasis formation of cancer cells. These were achieved through inhibiting epithelial-to-mesenchymal transition, inducing oxidative and nitrosative stress, and boosting antitumor immune response. Increased oxidative/nitrosative stress was due to the IPA-mediated downregulation of nuclear factor erythroid 2-related factor 2 (NRF2), upregulation of inducible nitric oxide synthase (iNOS), and enhanced mitochondrial reactive species production. Increased oxidative/nitrosative stress led to cytostasis and reductions in cancer cell stem-ness. IPA exerted its effects through aryl hydrocarbon receptor (AHR) and pregnane X receptor (PXR) receptors. A higher expression of PXR and AHR supported better survival in human breast cancer patients, highlighting the importance of IPA-elicited pathways in cytostasis in breast cancer. Furthermore, AHR activation and PXR expression related inversely to cancer cell proliferation level and to the stage and grade of the tumor. The fecal microbiome’s capacity for IPA biosynthesis was suppressed in women newly diagnosed with breast cancer, especially with stage 0. Bacterial indole biosynthesis showed correlation with lymphocyte infiltration to tumors in humans. Taken together, we found that IPA is a cytostatic bacterial metabolite, the production of which is suppressed in human breast cancer. Bacterial metabolites, among them, IPA, have a pivotal role in regulating the progression but not the initiation of the disease.

In breast cancer patients, the diversity of the microbiome decreases, coinciding with decreased production of cytostatic bacterial metabolites like lithocholic acid (LCA). We hypothesized that LCA can modulate oxidative stress to exert cytostatic effects in breast cancer cells. Treatment of breast cancer cells with LCA decreased nuclear factor-2 (NRF2) expression and increased Kelch-like ECH associating protein 1 (KEAP1) expression via activation of Takeda G-protein coupled receptor (TGR5) and constitutive androstane receptor (CAR). Altered NRF2 and KEAP1 expression subsequently led to decreased expression of glutathione peroxidase 3 (GPX3), an antioxidant enzyme, and increased expression of inducible nitric oxide synthase (iNOS). The imbalance between the pro- and antioxidant enzymes increased cytostatic effects via increased levels of lipid and protein oxidation. These effects were reversed by the pharmacological induction of NRF2 with RA839, tBHQ, or by thiol antioxidants. The expression of key components of the LCA-elicited cytostatic pathway (iNOS and 4HNE) gradually decreased as the breast cancer stage advanced. The level of lipid peroxidation in tumors negatively correlated with the mitotic index. The overexpression of iNOS, nNOS, CAR, KEAP1, NOX4, and TGR5 or the downregulation of NRF2 correlated with better survival in breast cancer patients, except for triple negative cases. Taken together, LCA, a metabolite of the gut microbiome, elicits oxidative stress that slows down the proliferation of breast cancer cells. The LCA–oxidative stress protective pathway is lost as breast cancer progresses, and the loss correlates with poor prognosis.

Rosacea is a common chronic inflammation of sebaceous gland-rich facial skin characterized by severe skin dryness, elevated pH, transepidermal water loss, and decreased hydration levels. Until now, there has been no thorough molecular analysis of permeability barrier alterations in the skin of patients with rosacea. Thus, we aimed to investigate the barrier alterations in papulopustular rosacea samples compared with healthy sebaceous gland-rich skin, using RNA sequencing analysis (n = 8). Pathway analyses by Cytoscape ClueGO revealed 15 significantly enriched pathways related to skin barrier formation. RT-PCR and immunohistochemistry were used to validate the pathway analyses. The results showed significant alterations in barrier components in papulopustular rosacea samples compared with sebaceous gland-rich skin, including the cornified envelope and intercellular lipid lamellae formation, desmosome and tight junction organizations, barrier alarmins, and antimicrobial peptides. Moreover, the barrier damage in papulopustular rosacea was unexpectedly similar to atopic dermatitis; this similarity was confirmed by immunofluorescent staining. In summary, besides the well-known dysregulation of immunological, vascular, and neurological functions, we demonstrated prominent permeability barrier alterations in papulopustular rosacea at the molecular level, which highlight the importance of barrier repair therapies for rosacea.

Langerhans cell histiocytosis (LCH) is a rare neoplastic disease originating from cells characterized by antigen-presenting Langerhans cell phenotype. The clinical spectrum of LCH is highly variable including localized and disseminated forms mostly occurring in children. Recently, about 60% of LCHs were reported to carry the activating BRAF mutation V600E. In our retrospective study, we evaluated the occurrence and prognostic impact of the V600E mutation in formaldehyde-fixed, paraffin-embedded samples from 15 pediatric LCH cases treated at our institution. Allele-specific polymerase chain reaction (PCR) and direct sequencing were used to demonstrate the presence of V600E mutation, and immunohistochemistry (IHC) using the mutant protein-specific VE1 antibody clone was performed to confirm mutant BRAF protein expression. Eight of 15 (53.3%) cases proved to be BRAF mutants by any of the methods applied, with a single case showing a discrepancy (PCR negative/IHC positive). Four of the BRAF-mutant cases (50.0%) showed refractory disease and progressed to death within 43 months, whereas the remaining mutant cases were stable and responded well to therapy. Wild-type BRAF cases (7/15, 46.6%) with generally comparable initial presentation were all treated successfully. In conclusion, activating V600E BRAF mutation can be frequently demonstrated in pediatric LCH by both allele-specific PCR and IHC. Unfavorable risk cases potentially also responding to BRAF-inhibitory therapy can be identified by mutation testing using archival formaldehyde-fixed, paraffin-embedded tumor samples.

Biliary tract cancer (BTC) is a rare malignancy with a long disease course and an overall poor prognosis. Despite multiple chemotherapy agents, there is no defined second-line treatment opportunity for advanced BTCs. In the era of precision oncology, NGS plays an important role in identifying mutations that may predict the molecular pathomechanism and manage the BTC therapy. The peripheral blood liquid biopsy (LB) of cancer patients represents variable amounts of cell-free DNA (cfDNA) released from tumor foci of any anatomical location. Our study aimed to identify somatic mutations and tumor variant burden (TVB) in cell-free and matched tumor DNA. We found a positive correlation between the estimated tumor volume and cfDNA yield (r = 0.9326, p < 0.0001). Comparing tissue and LB results, similar TVB was observed. SNVs were proven in 84% of the cases, while in two cases, only the LB sample was informative for molecular analysis. The most important aberrations in BTCs, such as FGFR2, IDH1, IDH2, KRAS, and TP53, could be detected in matched LB samples. Our prospective study demonstrates a minimally invasive testing approach to identify molecular genetic alterations in cholangiocarcinoma and gallbladder cancers. Clinical applications of cfDNA reflect by capturing the outstanding spatial tumor heterogeneity and guarantee novel aspects for the precision oncology treatment.