Materials and methods
A retrospective analysis was conducted of patients with salivary gland
malignancies treated at a London teaching hospital. We searched the
pathology, radiation therapy and surgery databases for all major and
minor salivary gland neoplasms treated by surgery from 2004 to 2019. We
included only the malignant salivary gland tumours treated by primary
curative-intent surgery. We excluded benign neoplasms, malignant tumours
treated by palliative intent, and patients with fewer than six months of
follow-up. Clinical details, pathology, treatment and survival data were
obtained from the electronic and paper medical records. Survival data
were enriched in some cases by contacting GP surgeries, referring
hospitals and patients or their families. There were a few patients who
had a part of the definitive surgery done at another centre, and who
were subsequently referred to us for completion surgery and/or neck
dissection. The date of initial surgery was used for the survival
analysis in these patients.
SPSS version 21 (IBM Corp®) was utilized for the statistical analysis.
We assessed the distribution of various clinicopathological factors,
such as age, gender, site, margin status, pT classification, pN
classification, extra-nodal extension (ENE), lymphovascular invasion
(LVI), perineural invasion (PNI), TNM stage of disease (AJCC,
8th Ed., 2017), and adjuvant radiation therapy.
Tumours were grouped into higher-grade (carcinoma ex pleomorphic
adenoma, salivary duct carcinoma, high-grade mucoepidermoid carcinoma,
intermediate and high-grade adenoid cystic carcinoma, adenocarcinoma,
poorly-differentiated carcinoma, squamous cell carcinoma, neuroendocrine
carcinoma, spindle cell carcinoma and Merkel cell tumour) and
lower-grade (acinic cell carcinoma, mammary analogue secretory
carcinoma, low- and intermediate-grade mucoepidermoid carcinoma,
low-grade adenoid cystic carcinoma, epithelial myoepithelial carcinoma).
Margins ≥ 5 mm were considered negative, 1-<5 mm were
considered close, and <1 mm were considered positive. The
survival analysis was conducted by the Kaplan-Meier method, and
comparison between groups was determined with the log rank test. A
multivariate analysis was undertaken using Cox regression to assess the
impact of clinicopathological factors on overall survival (OS) and
disease-free survival (DFS).