Emerging evidence highlights the crucial role of gastrointestinal microbiota in the pathogenesis of gastric cancer. Helicobacter pylori (H. pylori) infection stands out as a primary pathogenic factor. However, interventions such as anti-H. pylori therapy, gastric surgeries, immunotherapy, and chronic inflammation significantly remodel the gastric microbiome, implicating a broader spectrum of microorganisms in cancer development. These microbial populations can modulate gastric carcinogenesis through various mechanisms, including sustained chronic inflammation, bacterial genotoxins, alterations in short-chain fatty acids, elevated gastrointestinal bile acids, impaired mucus barrier function, and increased concentrations of N-nitrosamines and lactic acid. The dynamic changes in gut microbiota also critically influence the outcomes of anti-cancer therapies by modifying drug bioavailability and metabolism, thus affecting therapeutic efficacy and side effect profiles. Additionally, the effectiveness of radiotherapy can be significantly impacted by gut microbiota alterations. Novel therapeutic strategies targeting the microbiome, such as dietary interventions, probiotic and synbiotic supplementation, and fecal microbiota transplantation, are showing promise in cancer treatment. Understanding the intricate relationship between the gut microbiota and gastric cancer is essential for developing new, evidence-based approaches to the prevention and treatment of this malignancy.

The COVID-19 pandemic is a significant worldwide health crisis. Breast cancer patients with COVID-19 are fragile and require particular clinical care. This study aimed to identify the clinical characteristics of breast cancer patients with COVID-19 and the risks associated with anti-cancer treatment. The medical records of breast cancer patients with laboratory-confirmed COVID-19 were collected among 9559 COVID-19 patients from seven designated hospitals from 13th January to 18th March 2020 in Hubei, China. Univariate and multivariate analyses were performed to assess risk factors for COVID-19 severity. Of the 45 breast cancer patients with COVID-19, 33 (73.3%) developed non-severe COVID-19, while 12 (26.7%) developed severe COVID-19, of which 3 (6.7%) patients died. The median age was 62 years, and 3 (6.7%) patients had stage IV breast cancer. Univariate analysis showed that age over 75 and the Eastern Cooperative Oncology Group (ECOG) score were associated with COVID-19 disease severity (P < 0.05). Multivariate analysis showed that patients who received chemotherapy within 7 days had a significantly higher risk for severe COVID-19 (logistic regression model: RR = 13.886, 95% CI 1.014–190.243, P = 0.049; Cox proportional hazards model: HR = 13.909, 95% CI 1.086–178.150, P = 0.043), with more pronounced neutropenia and higher LDH, CRP and procalcitonin levels than other patients (P < 0.05). In our breast cancer cohort, the severity of COVID-19 could be associated with baseline factors such as age over 75 and ECOG scores. Chemotherapy within 7 days before symptom onset could be a risk factor for severe COVID-19, reflected by neutropenia and elevated LDH, CRP and procalcitonin levels.