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

Abstract

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.

Recent developments in the pathology of primary pulmonary salivary gland‐type tumours

“…At least 11 primary pulmonary cases have been reported, occurring in 52-75-yearold adults and located in a main or lobar bronchus. 2,[199][200][201] Sialadenoma papilliferum is composed of an exophytic component with papillary stratified squamous epithelium and a contiguous endophytic, nonciliated, glandular component with a basal layer. 202 Eosinophilic luminal material and intraluminal projections are typical.…”

“…2 BRAF V600E mutation is characteristic of conventional sialadenoma papilliferum in the head and neck 203 and was detected in 40% of pulmonary sialadenoma papilliferum. 2,199,200 Sialadenoma papilliferum may be distinguished from mixed squamous and glandular papillomas (which can also harbour BRAF V600E mutations 204 ) by the absence of ciliated cells and positive SOX10 staining in the ductal component of sialadenoma papilliferum. 2,[199][200][201] Distal-type bronchiolar adenoma/ ciliated muconodular papillary tumours (BA/CMPT) may also harbour BRAF V600E mutation, lack ciliated cells, and may show squamous metaplasia, but stain positive for TTF-1 in the luminal layer and are peripherally located, unlike sialadenoma papilliferum.…”

“…2,199,200 Sialadenoma papilliferum may be distinguished from mixed squamous and glandular papillomas (which can also harbour BRAF V600E mutations 204 ) by the absence of ciliated cells and positive SOX10 staining in the ductal component of sialadenoma papilliferum. 2,[199][200][201] Distal-type bronchiolar adenoma/ ciliated muconodular papillary tumours (BA/CMPT) may also harbour BRAF V600E mutation, lack ciliated cells, and may show squamous metaplasia, but stain positive for TTF-1 in the luminal layer and are peripherally located, unlike sialadenoma papilliferum. 2,205 Although primary head and neck sialadenoma papilliferum can have malignant transformation, none of the reported pulmonary cases recurred after excision.…”

“…2,[199][200][201] Distal-type bronchiolar adenoma/ ciliated muconodular papillary tumours (BA/CMPT) may also harbour BRAF V600E mutation, lack ciliated cells, and may show squamous metaplasia, but stain positive for TTF-1 in the luminal layer and are peripherally located, unlike sialadenoma papilliferum. 2,205 Although primary head and neck sialadenoma papilliferum can have malignant transformation, none of the reported pulmonary cases recurred after excision. 2…”

“…Primary pulmonary salivary gland-type tumours are rare neoplasms that are thought to arise from submucosal seromucinous glands in large airways. Therefore, most of these neoplasms are located centrally in the lung, [1][2][3][4][5][6] potentially obstructing large airways and resulting in postobstructive changes of the lung.…”