ASP1012 is being studied to see how well it works against solid tumors, which are lumps of cancer cells. This study involves adults whose tumors have spread or grown. ASP1012 is a special virus that targets cancer cells while leaving healthy cells alone. Sometimes, it will be given with another medicine called pembrolizumab to see if they work well together.

The study has three parts:

• Part 1: People will get different doses of ASP1012 to find the best amount.
• Part 2: More people, especially those with skin cancer (melanoma), will try the most suitable dose. Some will get the medicine combo.
• Part 3: People with stomach, ovarian, or colorectal cancer may join if they respond well in previous parts.

Each treatment cycle lasts 21 days, and people can have more cycles if they respond well, except those with melanoma on the combo treatment. Participants must visit the clinic, sometimes virtually, for checkups and tests like blood draws and scans. The study will also check for any side effects of the treatment.

• Study length: Each cycle is 21 days, starting with 3 cycles.
• Visits: Clinic visits for checkups, some virtual or by phone.
• Risks: Possible side effects from ASP1012 and the combo treatment.