The introduction of immune checkpoint inhibitors has constituted a major revolution in the treatment of patients with cancer. In contrast with the traditional cytotoxic therapies that directly kill tumor cells, this treatment modality enhances the ability of the host’s immune system to recognize and target cancerous cells. While immune checkpoint inhibitors have been effective across multiple cancer types, overcoming resistance remains a key area of ongoing research. The gut microbiota and its role in cancer immunosurveillance have recently become a major field of study. Gut microbiota has been shown to have direct and systemic effects on cancer pathogenesis and hosts anti-tumor immune response. Many studies have also shown that the host microbiota profile plays an essential role in the response to immunotherapy, especially immune checkpoint inhibitors. As such, modulating this microbial environment has offered a potential path to overcome the resistance to immune checkpoint inhibitors. In this review, we will talk about the role of microbiota in cancer pathogenesis and immune-system activity. We will also discuss preclinical and clinical studies that have increased our understanding about the roles and the mechanisms through which microbiota influences the response to treatment with immune checkpoint inhibitors.

Immunotherapy has changed the treatment paradigm in multiple solid and hematologic malignancies. However, response remains limited in a significant number of cases, with tumors developing innate or acquired resistance to checkpoint inhibition. Certain “hot” or “immune-sensitive” tumors become “cold” or “immune-resistant”, with resultant tumor growth and disease progression. Multiple factors are at play both at the cellular and host levels. The tumor microenvironment (TME) contributes the most to immune-resistance, with nutrient deficiency, hypoxia, acidity and different secreted inflammatory markers, all contributing to modulation of immune-metabolism and reprogramming of immune cells towards pro- or anti-inflammatory phenotypes. Both the tumor and surrounding immune cells require high amounts of glucose, amino acids and fatty acids to fulfill their energy demands. Thus, both compete over one pool of nutrients that falls short on needs, obliging cells to resort to alternative adaptive metabolic mechanisms that take part in shaping their inflammatory phenotypes. Aerobic or anaerobic glycolysis, oxidative phosphorylation, tryptophan catabolism, glutaminolysis, fatty acid synthesis or fatty acid oxidation, etc. are all mechanisms that contribute to immune modulation. Different pathways are triggered leading to genetic and epigenetic modulation with consequent reprogramming of immune cells such as T-cells (effector, memory or regulatory), tumor-associated macrophages (TAMs) (M1 or M2), natural killers (NK) cells (active or senescent), and dendritic cells (DC) (effector or tolerogenic), etc. Even host factors such as inflammatory conditions, obesity, caloric deficit, gender, infections, microbiota and smoking status, may be as well contributory to immune modulation, anti-tumor immunity and response to immune checkpoint inhibition. Given the complex and delicate metabolic networks within the tumor microenvironment controlling immune response, targeting key metabolic modulators may represent a valid therapeutic option to be combined with checkpoint inhibitors in an attempt to regain immune function.

Breast cancer is the most commonly diagnosed cancer in women and the second leading cause of cancer-related death worldwide. Positive family history increases the likelihood of developing this disease. As late-stage presentation and poor survival rates are associated with a lack of knowledge about breast cancer and its screening methods, this study aimed to evaluate the knowledge of Lebanese women with first-degree relatives who were diagnosed with breast cancer. In this cross-sectional study, 200 women with a positive family history accompanying their relatives to oncology clinics or the infusion center at the American University of Beirut Medical Center, completed an online survey after institutional review board approval was granted. Demographic information and answers to questions related to breast cancer risk factors, warning signs, and screening techniques were collected and analyzed using descriptive statistics and chi-square tests. Eighty-one percent of the study participants agreed that a history of breast cancer is associated with a higher disease risk. The smaller portions were aware of other potential risk factors, such as hormone replacement therapy, alcohol consumption, late menopause, early menarche, and overweight and sedentary lifestyles. Also, 93% to 96.5% of the participants recognized breast self-examination and mammography as useful tools for early detection. Furthermore, younger participants who reached university level and were employed had more insights into breast cancer. Breast cancer knowledge and early diagnosis are key elements in preventing late presentations and reducing the associated morbidity and mortality. Further educational and awareness campaigns should be conducted in Lebanon to improve women knowledge of breast cancer.

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