A method of preserving haptenized tumor cells is described. The method employs a freezing medium containing an effective amount of sucrose and human serum albumin in an isotonic buffered saline solution. Cryogenically preserving haptenized cells in such a medium has been found to maintain the integrity of the tumor cells during storage. The haptenized tumor cells also retain cell-associated antigens and haptens, and are as immunogenic, i.e., capable of inducing immunotherapeutic response, as fresh vaccine in a mouse model of metastatic disease. In a specific embodiment, haptenized cells are exposed to a solution of 8% sucrose, 10% human serum albumin in Hank's buffered solution, and then frozen to −80° C. overnight and then stored in a liquid nitrogen freezer. Methods of storing haptenized tumor cells and compositions are also provided.