Session Item

Median survival in metastatic/recurrent HNC (M/R HN-SCC) is less than 1 year, and locoregional recurrence (LRR) is the main cause of cancer-related death. Combined local and systemic therapies are required in order to achieve better results. Stereotactic body radiotherapy (SBRT), which can work synergistically with immune checkpoint inhibitors (ICI), can be a promising treatment option with more satisfactory response rates. We frequently apply 3x8 Gy SBRT concurrently with ICI in patients with M/R HN-SCC, and this study aims to share the clinical results and toxicity profile of these patients.

Fifteen patients diagnosed with M/R HN-SCC were evaluated retrospectively. All patients received SBRT to all metastatic and recurrent foci with concurrent ICI. Toxicity was evaluated according to the Radiation Therapy Oncology Group (RTOG) and the European Organization for Research and Treatment of Cancer (EORTC) criteria.

The median age at the time of diagnosis was 57 years (range: 19-80 years). Four patients were female, and 11 were male. A total of 25 lesions were irradiated in 15 patients between January 2019 and July 2020. Sixteen of these lesions were re-irradiation, and three of them received the 3^rd course of RT. At the last control, four patients were dead; one was due to disease progression. Eight patients had complete responses, one had a partial response, four had stable diseases, and two had progressive diseases. None of the lesions irradiated via SBRT with concurrent ICI progressed during the follow-up except for one. Therefore, the SBRT-C rate was 96%. The 6-, 12-, and 24-month OS rate was 93%, 76%, and 57%; the PFS rate was 86%, 50% and 33%, %the LRFS rate was 86%, 70%, and 53%, the RRFS rate was 86%, 65%, and 49%, and the DMFS rate was 93%, 61%, and 46%, respectively. Mean OS was 21.2 months (standard error [SE]:2.2, 95% confidence interval [CI]: 17.7-25.7) and mean PFS was 16.2 months (SE: 2.4, 95% CI: 11.4-20.9). The abscopal effect was observed in two patients who both had nasopharyngeal cancer. Acute grade 1 SBRT-related dermatitis was observed in only one patient and no other acute side effects were observed. A stent was placed in the carotid artery in two patients prior to re-irradiation due to the late SBRT-related carotid blowout syndrome (CBOS) risk. In one patient CBOS could be prevented but the other patient succumbed to CBOS. Other late SBRT-related side effects were observed in three patients (dysphagia, pituitary insufficiency, skull base osteomyelitis). A total of five patients developed ICI-related toxicity (recall dermatitis in one patient and hypothyroidism in four patients).

By using ICI and SBRT concurrently, we have achieved excellent OS and PFS and also achieved satisfactory outcomes in HN-SCC re-irradiation which is one of the most challenging areas of RT.