Nodal Metastasis in Low Grade Salivary Gland Carcinoma: A Retrospective Analysis of Incidence, Histologic Spectrum and Outcome.

Background: Lymph node metastasis is an adverse pathologic feature that often necessitates post-operative adjuvant radiation therapy or concurrent chemoradiation for salivary gland carcinoma (SGC). While regional metastasis is more common in high grade SGCs, it is rare in low grade (LG) SGCs.

Methods: In this retrospective study, we conducted a detailed review of a retrospective cohort of 543 LG-SGCs. Nodal metastasis at presentation and regional recurrence were identified in 7% (n = 38) and 3% (n = 14) of LG-SGCs respectively. The incidence of nodal metastasis varied by tumor histologic subtype, ranging from 0% for epithelial-myoepithelial carcinoma to 10% for polymorphous adenocarcinoma. Compared with LG-SGCs without nodal metastasis, those with regional metastasis were associated with a significantly higher frequency of pT4 disease, larger tumor size, lymphovascular invasion, and perineural invasion. However, clinical outcomes did not differ significantly between the two groups. The 5-year disease-specific survival was 100% and 99% respectively for pN + and pNx/pN0 groups, while the 5-year disease-free survival was 82% and 93% respectively. Among the LG-SGCs that developed regional recurrence to neck lymph nodes, the time between primary resection and recurrent disease ranged from 6 to 233 months (median = 64 months).

Conclusion: Nodal metastasis, though rare, occurs in 7% of patients with LG-SGCs at the time of diagnosis and in 3% as a recurrent disease. It is associated with pT4 disease, larger tumor size, perineural and lymphovascular invasion but does not appear to significantly impact clinical outcomes.