Exploring the prognostic and predictive potential of bacterial biomarkers in non-gastrointestinal solid tumors.

Introduction: Standard clinical parameters like tumor size, age, lymph node status, and molecular markers are used to predict progression risk and treatment response. However, exploring additional markers that reflect underlying biology could offer a more comprehensive understanding of the tumor microenvironment (TME). The TME influences tumor development, progression, disease severity, and survival, with tumor-associated bacteria posited to play significant roles. Studies on tumor-associated microbiota have focused on high bacterial-load sites such as the gut, oral cavity, and stomach, but interest is growing in non-gastrointestinal (GI) solid tumors, such as breast, lung, and pancreas. Microbe-based biomarkers, including Helicobacter pylori, human papillomavirus (HPV), and hepatitis B and C viruses, have proven valuable in predicting gastric, cervical, and renal cancers.

Areas covered: Potential of prognostic and predictive bacterial biomarkers in non-GI solid tumors and the methodologies used.

Expert opinion: Advances in techniques like 16S rRNA gene sequencing, qPCR, immunostaining, and in situ hybridization have enabled detailed analysis of difficult-to-culture microbes in solid tumors. However, to ensure reliable results, it is critical to standardize protocols, accurately align reads, address contamination, and maintain proper sample handling. This will pave the way for developing reliable bacterial markers that enhance prognosis, prediction, and personalized treatment planning.