This study will test the safety of a study drug called CRD3874-SI. The researchers will test
different doses of CRD3874-SI to find the highest dose that causes few or mild side effects
in participants. After the researchers find the highest safe dose of CRD3874-SI, they will
test that dose in new groups of participants to help them learn more about the side effects
of the study drug and find out whether CRD3874-SI is an effective treatment for for patients
with advanced or metastatic malignant solid tumors including sarcoma and Merkel Cell
Carcinoma.