Fibroblast activation protein (FAP) is a cell surface protein that is highly expressed on the surface of cancer-associated fibroblasts (CAFs) present in the tumor microenvironment of most epithelial cancers, whereas limited expression of FAP is observed in normal tissues. In some cancers of mesenchymal origin, notably sarcoma and mesothelioma, FAP expression has also been observed on the tumor cells themselves. Given the restricted expression profile, FAP is a promising target for peptide-targeted radionuclide imaging and therapeutic agents. Phase 1 of this study is designed to evaluate the safety and establish the recommended intravenous (IV) Phase 2 dose (RP2D) for \[177Lu\]Lu FAP 2286 monotherapy in participants with FAP expressing solid tumors. Phase 2 is designed to evaluate the safety and efficacy of \[177Lu\]Lu FAP 2286 as monotherapy in participants with pancreatic ductal adenocarcinoma (PDAC), non-small cell lung cancer (NSCLC), and breast cancer (BC) and in combination with chemotherapy in participants with untreated PDAC or relapsed NSCLC. Participants in both Phase 1 and 2 will be selected for treatment with \[177Lu\]Lu FAP 2286 based on \[68Ga\]Ga FAP 2286 imaging for determining tumor FAP expression.