Metastatic tumours to the parotid: A 20-year single institutional experience with an emphasis on 14 unusual presentations

The parotid gland is a rare site for distant metastasis. We aim to provide an overview of metastatic tumours to the parotid over the past 20 years, focusing on clinicopathological analysis of 14 rare diagnoses. To the best of our knowledge, we are the first group to present the most up-to-date and largest case series on unusual metastases to the parotid. A total of 93 metastatic cases were identified from 2004 to 2023, on the pathology information system at North West London Pathology, with squamous cell carcinoma (n = 45, 48.4 %) as the most common primary, followed by malignant melanoma (n = 29, 31.2 %) and Merkel cell carcinoma (n = 4, 4.3 %). We came across 14 rare tumours that had metastasised to the parotid, including metastatic adenocarcinoma from kidney (n = 3, 3.2 %), lung (n = 3, 3.2 %) and breast (n = 1, 1.1 %), olfactory neuroblastoma (n = 3, 3.2 %), soft tissue sarcoma (n = 2, 2.2 %), small cell carcinoma (n = 1, 1,1 %) and hidradenocarcinoma (n = 1, 1.1 %). Half of all secondary neoplastic lesions (50.5 %) were found in intra-parotid nodes, while the other half (49.5 %) were found in parotid parenchyma. Our study offers valuable insights into the various tumour types that can metastasise to the parotid across a wide age range. It underscores the necessity of maintaining a broad differential diagnosis. Keeping an open mind regarding the potential primary sources of the tumour is imperative for accurate diagnosis and effective treatment planning.