This is a first-in-human, Phase 1, non-randomized, multicenter, open-label clinical study designed to investigate the safety, tolerability, dosimetry, biodistribution, and pharmacokinetics (PK) of \[225Ac\]-FPI-2068, \[111In\]-FPI-2107, and FPI-2053 in metastatic and/or recurrent solid tumors (HNSCC, NSCLC, mCRC, PDAC, GC, RCC).