Understanding primary parotid squamous cell carcinoma - A systematic review.

Abstract

Introduction The true incidence of primary parotid squamous cell carcinoma (SCC) is unknown and likely overestimated in the literature. The aim of this systematic review is to examine the diagnosis, aetiology and incidence of parotid SCC by analysing studies evaluating primary parotid SCC.

Results A total of 14 observational retrospective studies on primary parotid SCC were included. There are currently no standard criteria for ascertainment of primary parotid SCC. Primary parotid SCC is thought to be due to squamous metaplasia within the ductal epithelium and subsequent invasive squamous carcinoma. Histological features that favour primary disease includes SCC confined to parotid parenchyma with no direct communication to the skin and the absence of mucin. Incidence of primary parotid SCC varied from 1.54 to 2.8 cases per million person-years. Around 30%–86% of patients recorded to have primary parotid SCC on clinical records, when scrutinised, were in fact secondary to parotid lymph node involvement following regional advancement from skin or upper aerodigestive tract SCC.

Conclusion Primary parotid SCC is rare and it is currently a diagnosis of exclusion. Thorough clinical assessment including endoscopy, preoperative imaging and the scrutiny of histopathological findings allow for differentiation between primary and secondary SCC within the parotid. This thus affects both initial treatment and subsequent follow-up.

Highlights •Primary parotid SCC is currently a diagnosis of exclusion.•Criteria for ascertainment of primary parotid SCC varies in the literature.•Combination of detailed clinical assessment, endoscopic assessment, cross-sectional imaging and histological assessment is required to differentiate between primary and metastatic parotid SCC.•30%–86% of patients recorded to have primary parotid SCC on clinical records were actually metastatic SCC.