Pulmonary sialadenoma papilliferum and its mimics: what you need to know.

Pumonary salivary gland-type tumours (SGT) represent a small but distinct group of primary lung neoplasms. These types of tumours originate from the submucosal bronchial glands of the tracheobronchial tree. Pulmonary SGTs differ greatly in the incidence of individual tumours from salivary gland tumours of the head and neck. Additionally, the vast majority of pulmonary SGT are malignant. Recently, pathological diagnosis has significantly improved with the application of molecular diagnostic technologies. However, the current knowledge of benign SGTs is limited; moreover, tumour diversity and overlapping morphological features of SGT represent diagnostic challenges such as correct tumour categorisation and their accurate differentiation from malignant lesions. Compounding this inherent difficulty has been the recent introduction of new variants, including sialadenoma papilliferum (SP). Pulmonary SP is very rare, with limited reports available, and most of the initial diagnoses rendered so far were incorrect, resulting in inappropriate treatment. Several cases of SP have recently been reported. This review will serve to update practicing pathologists on the morphology, immunophenotype and molecular characteristics of SP and its mimics.