This study is a single-center, open-label first-in-human clinical study. Patients with clinically suspected or confirmed malignant solid tumors will undergo \[68Ga\]Ga-FAP PET imaging or \[177Lu\]Lu-FAP SPECT imaging as well as \[18F\]FDG PET imaging to determine the presence or absence of lesions, and to assess lesion location, characteristics, and metastasis. Histopathological diagnosis or follow-up results will serve as the reference standard. The diagnostic efficacy of \[68Ga\]Ga-FAP PET imaging or \[177Lu\]Lu-FAP SPECT imaging for malignant tumors will be evaluated. Additionally, the study will analyze the biodistribution and dosimetry of \[177Lu\]Lu-FAP following a single administration, explore the correlation between tumor uptake values on imaging and immunohistochemical FAP expression levels, and evaluate the safety and tolerability of a single low-dose intravenous injection of \[68Ga\]Ga-FAP or \[177Lu\]Lu-FAP for diagnostic imaging.