Adjuvant Radiotherapy in Patients with Squamous Cell Carcinoma of the Oral Cavity or Oropharynx and Solitary Ipsilateral Lymph Node Metastasis (pN1)—A Prospective Multicentric Cohort Study

SIMPLE SUMMARY: In brief, this is the first prospective study using a multicentric approach to investigate the effectiveness of adjuvant radiotherapy in patients with early squamous cell carcinoma of the oral cavity (T1/2) and the oropharynx (T1) with one single ipsilateral cervical lymph node metastasis (pN1) in terms of overall survival, time to progression, and quality of life. After the inclusion of 209 patients into this prospective multicentric comprehensive cohort study (2009–2021) and analyzing the follow-up data, we can conclude that adjuvant radiotherapy in patients with early squamous cell carcinoma of the oral cavity and oropharynx does not seem to influence overall survival, but it positively affects the time to progression. However, irradiated patients report a significantly decreased quality of life up to three years after therapy compared to the observation group. ABSTRACT: (1) Background: Evaluation of impact of adjuvant radiation therapy (RT) in patients with oral squamous cell carcinoma of the oral cavity/oropharynx (OSCC) of up to 4 cm (pT1/pT2) and solitary ipsilateral lymph node metastasis (pN1). A non-irradiated group with clinical follow-up was chosen for control, and survival and quality of life (QL) were compared; (2) Methods: This prospective multicentric comprehensive cohort study included patients with resected OSCC (pT1/pT2, pN1, and cM0) who were allocated into adjuvant radiation therapy (RT) or observation. The primary endpoint was overall survival. Secondary endpoints were progression-free survival and QL after surgery; (3) Results: Out of 27 centers, 209 patients were enrolled with a median follow-up of 3.4 years. An amount of 137 patients were in the observation arm, and 72 received adjuvant irradiation. Overall survival did not differ between groups (hazard ratio (HR) 0.98 [0.55–1.73], p = 0.94). There were fewer neck metastases (HR 0.34 [0.15–0.77]; p = 0.01), as well as fewer local recurrences (HR 0.41 [0.19–0.89]; p = 0.02) under adjuvant RT. For QL, irradiated patients showed higher values for the symptom scale pain after 0.5, two, and three years (all p < 0.05). After six months and three years, irradiated patients reported higher symptom burdens (impaired swallowing, speech, as well as teeth-related problems (all p < 0.05)). Patients in the RT group had significantly more problems with mouth opening after six months, one, and two years (p < 0.05); (4) Conclusions: Adjuvant RT in patients with early SCC of the oral cavity and oropharynx does not seem to influence overall survival, but it positively affects progression-free survival. However, irradiated patients report a significantly decreased QL up to three years after therapy compared to the observation group.