Disclosed is a method of obtaining an inorganic nanostructured complex (CFI-1), a protein-associated nanostructured complex (MRB-CFI-1) and antitumor use. The main use is in treating urinary bladder cancer, both in animals arid humans. The complex has singular antitumor activity, and can potentially be used as a substitute and/or act as an adjuvant for other commercial antineoplastic drugs.