Extracapsular extension is not a significant prognostic indicator in non-squamous cancers of the major salivary glands

Background: Extracapsular extension (ECE) is a well-established prognostic feature in squamous cell cancers of the head and neck. Although some extrapolate data from mucosal head and neck cancer to include ECE as a high-risk feature in salivary gland cancers, data is lacking about ECE's prognostic value for these malignancies. We investigate whether ECE is a significant prognostic indicator in pathologic node-positive cancers of the major salivary glands.

Methods: A retrospective study of adult salivary gland cancer cases diagnosed from 2004 to 2013 in the NCDB was conducted. Demographic, tumor, treatment, and survival variables were included in the study. Univariate Kaplan-Meier analyses, as well as multivariate Cox survival regressions were performed.

Results: Positive ECE status was associated with significantly worse survival in salivary SCC (HR 1.687; p = 0.002) but not non-squamous salivary cancers (HR 1.000; p = 0.998) on multivariate analysis. While post-operative radiotherapy was not associated with improved survival for patients without high-risk adverse features (high grade or positive surgical margins), its use was associated with better survival for ECE-positive salivary SCC patients without one of these additional adverse features (HR 0.064; p = 0.010).

Conclusions: Although ECE is a significant prognostic indicator in salivary SCC, its prognostic significance for non-squamous salivary cancers may be limited. Radiotherapy may improve survival in cases with at least one high-risk adverse feature: high grade; positive surgical margins; and for salivary SCC specifically, positive ECE status.