Apelin, a Circulating Biomarker in Cancer Evaluation: A Systematic Review

Simple Summary Despite advances in science and technology for the care of patients with cancer, providing effective treatment remains challenging. The lack of sensitive markers for early diagnosis and monitoring of cancer progression leads to suboptimal outcomes and decreased survival. There is a need to identify objective and reliable biomarkers that can be used in diagnosing, monitoring, and treating cancer. Apelin as a protein plays a role in cancer development and may predict treatment response and prognosis; however, research is limited. This review aims to synthesize current knowledge on associations of apelin circulating in blood with cancer and highlight knowledge gaps to direct future research. Results showed significant variations in methods of measuring apelin in the blood among various cancer studies and indicated inconsistent associations between apelin and clinical characteristics such as BMI, tumor pathology, and survival. Future research warrants more studies to advance in standardized measurement methods, produce a body of evidence based on the cancer types, and define the optimal cutoff points of apelin for accurate and early detection of cancer for personalized treatment. Apelin is a promising biomarker for the detection and prognosis of cancer. This review aims to synthesize current knowledge on associations of circulating apelin with cancer, illustrate knowledge gaps, and discuss future research. Following PRISMA guidelines, CINAHL, EMBASE, and PubMed were searched using terms cancer AND apelin between 2011 and 2021, full text, and English language. Inclusion criteria: measured circulating apelin in adults 18 years or older with cancer, and observational, cross-sectional, longitudinal, case-control, cohort, quasi-experimental, or randomized control trials. Excluded were studies with animal models, tissue samples only, secondary data analyses, systematic reviews, literature reviews, grey literature, and conference abstracts. 16 articles were included. There were significant variations in measurement methods between studies. Comparison of circulating apelin between cases and controls and associations of circulating apelin with clinicopathological characteristics were inconsistent. Variations in results suggest that the relationship between circulating apelin and cancer differs among cancer types. Differences in measurement methods between studies highlight the need for consistency in future research to draw meaningful conclusions. Future research should seek to standardize methods of detecting circulating apelin and examine its associations with specific cancer types to determine what role that circulating apelin may play in cancer development and progression.

Automated summary

Despite advances in science and technology, effective treatment for cancer remains challenging due to the lack of sensitive markers for early diagnosis and monitoring. This review aims to synthesize current knowledge on the association between circulating apelin and cancer, highlighting the need for standardized measurement methods and defining optimal cutoff points. The results showed inconsistent associations between apelin and clinical characteristics, suggesting that the relationship between apelin and cancer differs among cancer types. Future research should focus on standardizing measurement methods and investigating the role of circulating apelin in specific cancer types.