Minor salivary gland neoplasms may arise at several intraoral sites. At which of the following sites is a minor salivary gland tumour LEAST likely to occur?

Correct answer: D. Lower lip

• A. The retromolar region and buccal mucosa are recognised, if less frequent, sites for minor salivary gland neoplasms — still more likely than the lower lip.
• B. The UPPER LIP is the second most common intraoral site for minor salivary gland tumours. The contrast with the lower lip is one of the classic teaching points: a nodule in the UPPER lip is a salivary gland tumour (usually a benign pleomorphic adenoma or canalicular adenoma) until proven otherwise, whereas a nodule in the LOWER lip is a mucocele until proven otherwise.
• C. The HARD PALATE — specifically the posterior lateral hard palate — is the single MOST COMMON intraoral site for minor salivary gland tumours, both benign (pleomorphic adenoma) and malignant (mucoepidermoid carcinoma, adenoid cystic carcinoma, polymorphous adenocarcinoma).
• D. CORRECT — this is the LEAST likely site. Although the lower lip contains abundant minor salivary glands, it is remarkably rarely the site of a true NEOPLASM. The overwhelming majority of lower lip swellings arising from minor glands are MUCOCELES (mucus extravasation phenomena) caused by trauma to a duct — not tumours. When a discrete lump does appear on the lower lip, mucocele is the diagnosis until proven otherwise.

Note: Two rules worth memorising together. FIRST, the upper-lip/lower-lip contrast: upper lip nodule → think tumour; lower lip nodule → think mucocele. SECOND, the inverse size rule: the SMALLER the gland, the HIGHER the proportion of its tumours that are malignant. Parotid tumours are roughly 75–80% benign, submandibular roughly 50%, and minor salivary gland tumours are around 50% or more malignant. So a palatal salivary mass carries a substantially higher malignancy risk than a parotid mass, even though the parotid is the more common overall site.