Myoepithelial-Rich Pleomorphic Adenoma With Novel PLAG1 Inversion on Chromosome 8, and LRP1B, PBRM1 and TCF3 Mutations.

Pleomorphic adenoma (PA) is the most common salivary gland neoplasm worldwide (50%-70%). Most cases of PA are straightforward diagnoses. However, the diagnosis may be challenging due to the morphological diversity of PAs, which in many cases is caused by the predominance of one of the three components or the presence of metaplastic epithelium. We present the case of a 64-year-old male with a history of prostate cancer and right submandibular gland excision 16 years ago with an unknown previous diagnosis and recent regrowth of his mass in the surgical bed. The tumour showed a predominant spindle cell morphology, cytokeratin-positivity, variable expression of myoepithelial markers in the cytology and surgical pathology specimens, and novel inversion of the chromosome 8, and LRP1B, PBRM1 and TCF3 mutations.