N'-(2-Chloroethyl)-N-(2-(methylsulfonyl)-ethyl)-N'-nitrosourea (cystemustine) is a chloroethylnitrosourea that has been used in the treatment of human melanoma. Its main antitumor effect is DNA damage to malignant melanocytes. Although unreported at present, other effects may also account for its cytotoxicity, some of them could be more or less delayed with respect to its administration. In this report, we have developed a model of secondary tumor with B16 melanoma in syngeneic C57B16 recipients to investigate the impact of cystemustine treatment of primary B16 melanoma tumors on the fate of secondary implanted untreated tumors. The data presented in this report indicate that cystemustine-treated cells or the administration of cystemustine provoke an important growth delay of primary melanoma tumors, together with an increase in cell pigmentation and cell morphology changes. Data also show that prime treatment induces a dramatic decrease in tumor weight of secondary untreated tumors accompanied by an increase in melanin content and an alteration of cell morphology. Finally, 1H-NMR spectroscopy was performed on treated B16 cells, showing an alteration in the phospholipid derivatives of melanocytes, suggesting subsequent modifications of membrane phospholipid composition. In conclusion, the data highlight two important findings: (a) cystemustine produces modifications other than DNA damage, i.e., cell morphology changes, pigmentation, and phospholipid metabolism alterations, indicating an interference with cell cycle, cell redifferentiation, and proliferation programs; and (b) cystemustine-treated tumors appear to confer a protective effect against the development of secondary untreated tumors that may be mediated by cytokines or an immune response.