<qa>  What is the best way to treat solid tumors?This phase Ib trial studies the best way of TLR8 Agonist VTX-2337 and cyclophosphamide in treating patients with a solid tumor that has spread from the primary site place where it started to other places in the body metastatic, progressed for a long time persistent, come back recurrent, or is growing, spreading, or getting worse progressed. TLR8 Agonist VTX-2337 may stimulate the immune system in different ways and stop tumor cells from growing. Drugs used in chemotherapy, such as cyclophosphamide, work in different ways to stop the growth of tumor cells, either by killing the cells, by stopping them from dividing, or by stopping them from spreading. Giving TLR8 Agonist VTX-2337 together with cyclophosphamide may be a better treatment for solid tumors. 