This is a single-arm, single-center, exploratory clinical study. A total of 20 participants with metastatic pancreatic ductal adenocarcinoma (with liver or lung metastasis) who have experienced disease progression after or are intolerant to standard first-line chemotherapy (based on the AG regimen \[Albumin-bound Paclitaxel plus Gemcitabine\]) will be enrolled.The study aims to evaluate the safety, efficacy, and underlying immunological mechanisms of Multimodal Thermal Therapy (MTT) combined with a KRAS G12V mRNA vaccine, S-1, and Sintilimab.