Metastatic cutaneous squamous cell carcinoma to the parotid: Adjuvant radiotherapy and treatment outcomes

IntroductionAdjuvant radiotherapy is an established component in the management of metastatic cutaneous squamous cell carcinoma (SCC) involving the parotid gland. Radiotherapy technique, dose and volumes are seldom described sufficiently to allow close examination. We report our treatment outcomes and focus on treatment-related factors that affect outcomes in this cohort. MethodsWe performed a retrospective review of patients with metastatic cutaneous SCCs who underwent parotidectomy with or without ipsilateral neck dissection. All patients received adjuvant radiotherapy. Demographics, clinical data and treatment details were collected from an intuitional electronic database. Individual patient-level radiotherapy technique, volumes and doses were reviewed. ResultsBetween July 2008 and July 2018, 60 patients met our inclusion criteria. Median follow-up duration was 32.7 months. The mean age was 66.4 years. The majority of patients (49 patients) received full neck irradiation. The 2-year and 5-year loco-regional failure-free survival was 87% (95% confidence interval (CI): 0.74-0.93) and 71% (95% CI: 0.52, 0.83), respectively. The 2-year and 5-year overall survival was 76% (95% CI: 0.62, 0.85) and 60% (95% CI: 0.45, 0.72), respectively. There were 15 cases of loco-regional failures, with 6 cases with dermal involvement. Lymphovascular invasion (LVI) was associated with higher loco-regional failure (hazard ratio: 8.43, 95% CI: 1.85-38.39, P = 0.005) and cancer-specific mortality (hazard ratio: 5.40, 95% CI: 1.40-20.87, P = 0.015). Treatment technique, intensity-modulated radiation therapy (IMRT) vs 3D conformal radiotherapy (3D CRT), bolus use, perineural invasion (PNI) and surgical margins were not significantly associated with loco-regional failure. ConclusionWe demonstrated high loco-regional control rates with routine use of comprehensive adjuvant radiotherapy. The presence of LVI was identified as a strong predictor for recurrence. Further analysis will help to define optimal radiation dose and techniques.