Key Inclusion Criteria

          -  Histologically or cytologically confirmed unresectable or metastatic solid tumor

          -  Documented FGFR2 gene fusion, mutation, or amplification per local testing of blood
             and/or tumor

          -  Additional FGFR2 alterations/tumor types may be considered for the Part 1 dose
             escalation

          -  Part 2 dose expansion patients must additionally meet the group requirements detailed
             below.

               -  Group 1 - Patients must have unresectable or metastatic intrahepatic
                  cholangiocarcinoma with FGFR2 fusion previously treated with a pan-FGFR inhibitor

               -  Group 2 - Patients must have unresectable or metastatic intrahepatic
                  cholangiocarcinoma with FGFR2 fusion NOT previously treated with a pan-FGFR
                  inhibitor

               -  Group 3 - Patients must have unresectable or metastatic solid tumor with FGFR2
                  fusion other than ICC

               -  Group 4 - Patients must have unresectable or metastatic solid tumor with FGFR2
                  amplification

               -  Group 5 - Patients must have unresectable or metastatic solid tumor with an
                  oncogenic FGFR2 mutation

          -  Patient must have disease that is refractory to standard therapy, disease that has not
             adequately responded to standard therapy, disease for which standard or curative
             therapy does not exist, or the patient must be intolerant to or have declined standard
             therapy

          -  Patient must have measurable or evaluable disease per RECIST v1.1

          -  Patient has ECOG performance status of 0-2

        Key Exclusion Criteria

          -  Ongoing, clinically significant corneal or retinal disorder

          -  Patient has any of the following within 14 days prior to the first dose of RLY-4008:

               -  Platelet count < 75 x 10^9 /L

               -  Absolute neutrophil count (ANC) < 1 x 10^9 /L

               -  Hemoglobin < 8 g/dL (red blood cell transfusion and erythropoietin may be used to
                  reach 8 g/dL, but must have been administered at least 2 weeks prior to the first
                  dose of RLY-4008)

               -  Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) > 3 x the
                  upper limit of normal (ULN) if no hepatic metastases are present; > 5 x ULN if
                  hepatic metastases are present

               -  Total bilirubin > 1.5 x ULN; > 3 x ULN with direct bilirubin > 1.5 x ULN in
                  presence of Gilbert's disease

               -  Estimated (Cockcroft-Gault formula) or measured creatinine clearance < 50 mL/min

          -  QT interval corrected using Fridericia's formula (QTcF) > 480 msec or history of
             prolonged QT syndrome, Torsades de pointes or familial history of prolonged QT
             syndrome

          -  Clinically significant, uncontrolled cardiovascular disease

          -  CNS metastases or primary CNS tumor that is associated with progressive neurologic
             symptoms