Study design

We conducted a prevalence-based cost-of-illness study from the perspective of the public healthcare system (Ministry of Health), with a top-down approach, from January 2008 to December 2016. We defined prevalence-based as all OC patients were included, regardless of the level of severity or onset of the disease. A top-down approach was used because our estimates consist of allocating total national health care expenditures by type of care (inpatient and outpatient) among the OC sites by using the ICD-10 codes for each site of OC (i.e. we identified the portions of the total health expenditure due to OC sites).

All codes related to OC according to the 10^th Revision of the International Classification of Disease [ICD-10]) were included. Three anatomical regions were considered, as follows: lip (C00—malignant neoplasm of the lip), oral cavity (C02—malignant neoplasm of other and unspecified parts of the tongue, C03—malignant neoplasm of the gums, C04—malignant neoplasm of the floor of the mouth, C05—malignant neoplasm of the palate, and C06—malignant neoplasm of other and unspecified parts of the mouth) and the oropharyngeal region (C01—malignant neoplasm of the base of the tongue, C09—malignant neoplasm of the tonsil, and C10—malignant neoplasm of the oropharynx) [14].