Diagnostic cytology (the study of cells) is used when a dog presents with intraoral or extraoral mass.
Examination of the cells should yield a diagnosis of an inflammation, neoplasia or a mixed-cell population (both inflammatory and neoplastic).
Samples from the oral cavity can be collected using a swab, scrape, touch impression or fine needle. Unfortunately, not all masses exfoliate diagnostic samples. Rubbing a swab over an encapsulated mass usually will not yield a diagnostic/cellular sample.
Read more at dvm360: Intraoral Cytology