A Study of ASP388B Given by Itself and With Standard Therapies in Participants With Solid Tumors

This is an early development study of ASP388B in people with solid tumors. In this study, ASP388B will be given to people for the first time. It will be given by itself or together with standard cancer therapies. The main aims of the study are to check the safety of ASP388B and find the most suitable dose. This study will be in 2 parts. In Part 1, different small groups of people with solid tumors will receive lower to higher doses of ASP388B. Some groups will receive ASP388B by itself, and other groups will receive ASP388B with standard cancer therapies. Any medical problems will be recorded for each dose. This is to find suitable doses of ASP388B to use in Part 2 of the study, and to include the tumor types that responded well to ASP388B. In Part 2, other different small groups of people with the specific tumor types (from Part 1) will receive the most suitable doses worked out from Part 1. Some groups will receive ASP388B by itself, and other groups will receive ASP388B with standard cancer therapies. In both parts of the study, ASP388B will be given once in 3-week cycles. The standard cancer therapies will be given according to their approved label. ASP388B and the standard cancer therapies will be given slowly through a tube into a vein. This is called an infusion. In both parts of the study, safety checks will be done at each visit, and the doctors will continue to check for medical problems throughout the study.