Surgical extent and role of adjuvant radiotherapy of surgically resectable, low-grade parotid cancer

Background: Due to the rarity of low-grade parotid gland cancer and the diversity of histologic subtype, its optimal treatment modalities and prognostic factors have not been established yet. In this study, we aimed to identify the prognostic factors and adequate treatment modalities for patients with low-grade parotid gland cancer. Methods: We retrospectively analyzed clinico-pathologic data from 287 patients with low-grade parotid gland cancer from 1999 to 2018. Results: Recurrence-free survival, disease-specific survival, and overall survival rates at 10 years were 80.6%, 93.9%, and 84.4%, respectively. Among all patients, 56.1% received surgery alone, and the remaining 43.9% received surgery with adjuvant radiotherapy. Resection margin status and TNM stage were significant unfavorable prognostic factors. In patients with T1-2 tumor, surgical extent (total vs. less-than-total) did not show any significant effect on disease recurrence and patients’ survival, and the disease was controlled well if a negative surgical margin was obtained after surgery, even with microscopic clear margin of<1 mm. In patients with adverse pathologic features (positive margin, lymphovascular invasion, perineural invasion, extracapsular nodal spread, T3-4, and N1-3), adjuvant radiotherapy significantly decreased loco-regional recurrence. Conclusions: Oncological outcomes were good in patients with low-grade parotid gland cancer with surgery and radiotherapy. In patients with T1-2 low-grade parotid gland cancer, surgery alone showed good local control rate regardless of the extent of surgery, if a negative surgical margin was obtained after surgery. Adjuvant radiotherapy played a significant role in controlling loco-regional recurrence in patients with adverse pathologic features.