(angiotensin converting enzyme 2) OR (ACE2) OR (ACEH) OR (Renin Angiotensin System) OR (Angiotensin I converting Enzyme 2) AND (COVID-19) OR (Coronavirus) AND (head and neck) AND (oral cavity) OR (mouth) AND (saliva) OR (salivary gland) AND (oropharynx) AND (nasopharynx) OR (nasal cavity) AND (tongue) AND (buccal mucosa) AND (cancer) OR (carcinoma) AND (oral squamous cell carcinoma) AND (oral potentially malignant disorders) AND (thyroid) AND (single cell RNA sequencing) AND (immunohistochemistry) were used. This evidence concerns the gene ACE2 and oral cavity squamous cell carcinoma.