A novel therapeutic agent for solid cancer capable of hardening the cellular tissue itself of a solid cancer to induce death or growth inhibition of cancer cells, causing solidification of the tissue, is disclosed. The therapeutic agent for solid cancer is composed of a liquid composition containing as an active component an ethoxy-containing compound capable of undergoing polycondensation in a cellular tissue. The therapeutic agent for solid cancer is capable of hardening the cellular tissue itself of a solid cancer such as lung cancer to induce death or growth inhibition of cancer cells, causing solidification of the tissue. In conventional therapeutic methods, the risk of metastasis due to spreading of cancer cells through the bloodstream cannot be eliminated. In contrast, this therapeutic agent for solid cancer instantly surrounds cancer cells, so that the risk of metastasis can be largely reduced.