## 3 Results
### Response to Immunotherapy  
A clinical benefit (CB) from immunotherapy was observed in 77.9% of cases, whereas 22.1% did not experience such a benefit (NCB). At PET-2, 46 patients were classified as responders (CMR, PMR, or SMD), while 13 were deemed non-responders due to evidence of progressive metabolic disease. Figure 1 shows an example of a patient with SCC who experienced a CB after immunotherapy and also showed a metabolic response on PET-2. In contrast, Figure 2 illustrates the condition of a patient with metabolic progression on PET-2, classified as having NCB. \begin{table}
\begin{tabular}{c c} \hline
**Characteristics** & **N (Percentage)** \\ \hline
**Immunotherapy with respect to other therapies** & \\ As 1 st line & 46 (77.9\%) \\ After upfront surgery & 12 (20.3\%) \\ After upfront RT & 1 (1.7\%) \\ \hline
**PET-based response after 12 weeks (PERCIST)** & \\ CMR & 5 (8.4\%) \\ PMR & 39 (66.1\%) \\ SMD & 2 (3.3\%) \\ PMD & 13 (22\%) \\ \hline
**Best clinical response (BCR) to immunotherapy** & \\ CB & 46 (77.9\%) \\ NCB & 13 (22.1\%) \\ \hline
**Immunotherapy-related toxicity** & \\ Cardiovascular toxicity & 1 (1.7\%) \\ \hline
**Therapeutic-switch after immunotherapy failure** & \\ Chemotherapy & 2 (3.3\%) \\ Radiotherapy & 3 (5\%) \\ Palliative treatments & 8 (13.5\%) \\ \hline Progression-free survival (median, months) & 14.7 \\ \hline \end{tabular}
\end{table} 
Table 1: Cont. Figure 1: [18]FFDG PET/CT in an 88-year-old male with cutaneous squamous cell carcinoma of the right ear. (**A**) (**left column**): Baseline whole-body PET maximum-intensity projection showed a focal hypermetabolic lesion in the right ear (black arrow; SUV\({}_{\text{max}}\) 11). Corresponding fused PET/CT axial (middle) and coronal (bottom) images confirmed intense [18]FFDG uptake at the site of the cutaneous tumor (white arrows). (**B**) (**right column**): Follow-up whole-body PET MIP demonstrated complete metabolic resolution of the right-ear lesion (black arrow). Fused PET/CT axial (middle) and coronal (bottom) views likewise showed no residual [18]FFDG uptake at the prior tumor site (white arrows). The patient was classified as having clinical benefit (CB). The patient’s progression-free survival was 22 months. Figure 2: [18]FDG PET/CT in an 87-year-old female with cutaneous squamous cell carcinoma (SCC) of the right supraclavicular region. (**A**): Baseline whole-body PET maximum-intensity projection revealed a focal area of increased [18]FFDG uptake (SUV\({}_{\text{max}}\) 5) corresponding to the primary cutaneous lesion (arrow). (**B**): Follow-up PET performed 12 weeks after the start of immunotherapy showed persistent metabolic activity in the right supraclavicular lesion (arrow), along with the emergence of two new hypermetabolic foci in the sternal and right breast regions (circles), indicating disease progression. (**C**): Fused axial PET/CT images confirmed the right supraclavicular cutaneous lesion with a centrally necrotic core and increased peripheral uptake (SUV\({}_{\text{max}}\) 6.1; arrow). (**D**): Fused axial PET/CT demonstrates a newly developed, intensely [18]FFDG-avoid lesion in the right breast region (SUV\({}_{\text{max}}\) 8; arrow). Histological confirmation of disease progression was obtained. The patient was classified as having no clinical benefit (NCB) from immunotherapy and was switched to palliative treatment. Progression-free survival (PFS) was 6 months. Among those classified as responders at PET-2, all also demonstrated a clinical benefit based on clinical and dermatological evaluations. For the 13 non-responders, the absence of clinical benefit was established by dermatological evaluation along with histological confirmation in seven cases and cytological confirmation in one case (eight cases in total), with the remaining five cases being determined solely by objective assessment. Among patients who failed to respond to immunotherapy, subsequent therapeutic strategies included chemotherapy (n = 2), radiotherapy (n = 3), and palliative treatments (n = 8).