Radiation Therapy in the Management of Cutaneous Squamous Cell Carcinoma Metastatic to the Parotid: A 50-Year Single Institution Experience

Abstract

Cutaneous squamous cell carcinoma (cSCC) represents 20% of skin cancers of the head and neck, and metastatic spread to the parotid area lymph nodes (PALN) are found in 1-3% of cases. Herein, we present the updated results of the largest single institution experience using radiation therapy (RT) in the management of patients (pts) with PALN metastases from cSCC in North America. Our hypothesis is the addition of pts treated with modern RT would maintain acceptable efficacy with a favorable toxicity profile. With IRB approval, we retrospectively reviewed all pts diagnosed with cSCC metastatic to PALN treated at our institution with >6 months follow up. All pts were staged by the O'Brien staging system. Fifteen pts (10%) were treated preoperatively, 111 (72%) post operatively, and 28 (18%) with RT alone. Most pts were treated with three dimensional conformal RT (3DCRT) or a combination of 3DCRT and electron therapy (n = 112), while 31 pts were treated with intensity modulated RT (IMRT). There were 115 pts treated once daily fractionation and 39 pts being treated twice per day. We estimated disease control and survival, including local (parotid) control (LC), neck control (NC), local-regional control (LRC), distant metastasis free survival (DMFS), cause specific survival (CSS), and overall survival (OS) using the cumulative incidence method. Treatment toxicities were documented per CTCAEv3. From November 1969 to December 2019, 154 pts were included. Median age at RT initiation was 66 years (range, 28-89). Fifty-two pts (33.8%) had an unknown location of a primary, while the most common identifiable locations of a primary were the temple, helix, and forehead. Forty-eight percent of pts had P2 or P3 disease with 26 of these pts being N1 or N2. Forty-six percent of pts were current or former smokers. Median follow up for this cohort was 4.9 years (range, <0.1 - 34.0) with 8 pts being lost to follow up. The overall 10-year Kaplan-Meier estimates for LC, NC, LRC, DMFS, CSS, and OS were 82%, 93%, 77%, 92%, 76%, and 31%, respectively. Eighty-one percent of treatment failures occurred within 2 years of treatment. LC was improved with IMRT (100%) compared to non-IMRT (78%) treatment (p = 0.005), with no other outcomes differing between the cohorts. There were 31 treatment complications were reported with 13 being ³ grade 3. Our results represent the 10-year outcomes for the largest reported single institution experience of RT for cSCC metastatic to PALN showing favorable clinical outcomes with an acceptable toxicity profile. There was improved LC for pts treated with IMRT compared to 3DCRT/electrons; yet these did not translate to significant changes in other clinical outcomes.