Exploring traditional Chinese medicine tongue diagnosis in potential cancer identification: A scoping review

Traditional Chinese medicine (TCM) tongue diagnosis entails the systematic evaluation of morphological characteristics (tongue features) on both dorsal and ventral tongue surfaces. Recent advancements in research have highlighted the potential diagnostic relevance of specific tongue features for cancer detection and monitoring through various inspection methodologies. This scoping review aims to provide a comprehensive overview of tongue features investigated in relation to cancer detection.

A literature search for clinical studies (excluding case reports) that examined the application of tongue inspection for detecting cancer, recurrence, or metastasis was conducted. Extracted data included study characteristics, patient populations, inspection techniques, and diagnostic outcomes.

Twenty-four studies consisting of 14 case-control studies, 4 cross sectional studies, 5 observational study, and 1 prospective multicentred cohort were identified, involving a total of 5458 cancer patients and 7880 control participants. Documented tongue features included lingual flange protrusion, sublingual nodules, engorged sublingual veins, purple-bluish tongue, and variations in tongue coating thickness, etc. that were associated with different cancer types and metastasis. Using QUADAS-2, the overall quality was low with potentially high risk of bias in some key domains, especially participant selection and index test.

The findings from this review provide a foundation for future research questions aimed at high-level observational studies. Tongue inspection holds promise as a cost-effective, time-efficient, and non-invasive method for detecting cancers and metastasis. Based on quality assessment, the study highlights future needs such as more prospective, blinded interpretation, pre-specified thresholds, and transparent reporting to improve both methodological rigor and external validity.