The purpose of this study is to test the safety and efficacy of an investigational drug called APS001F when given with flucytosine (5-FC) for treatment of solid tumors. APS001F is a recombinant Bifidobacterium longum (a live bacteria normally found in the digestive tract) that has been modified to produce an enzyme, cytosine deaminase (CD). The patient will first receive an injection of APS001F followed by oral 5-FC. APS001F is expected to go to the site of the tumor(s) where the agent will produce CD enzyme. CD enzyme will convert the 5-FC into 5-fluorouracil (5-FU) which is a standard chemotherapy drug for several types of cancer. Additionally, some patients will also receive 10% maltose injection, a sugar that has been shown to enhance the growth and effectiveness of APS001F in animals. This is the first study where APS001F is being used in humans.