Table 1.
Number of included studies by type of cancer
| Cancer | Number of included studiesa |
|---|---|
| Base of tongue | 5 |
| Hypopharyngeal | 5 |
| Laryngeal | 10 |
| Oral | 18 |
| Oropharyngeal | 14 |
| Paranasal sinus | 1 |
| Pharyngeal | 4 |
| Tongue | 4 |
| Tonsillar | 13 |
| Waldeyer’s ring | 2 |
| Unclassifiable | 6 |
aSome of the articles reported more than one type of cancer and presented the data for each type separately, allowing the data for each type to be regarded as a separate study. As such, the total number of articles based on classification by cancer type does not equal the total number of included studies in the systematic review and meta-analysis.