Growth is one of the most complicated phenomena of life in its heterogeneity composed of the cooperation of myriads of single processes. This is exemplified by the realization that there exists not one cause of cancer but several groups often ethnically influenced. Species-specific variations occur during the neoplastic development, which exhibits two main phases: I. The change of body metabolism leading via the malignant transformation to a primary tumor; II. The further progression of the neoplastic disease. This introduction, as a brief review, deals with the first phase of neoplastic development examining as causative factors, environment and diet on a comparative approach; to this first phase also belong the cancer causing therapies of nonneoplastic diseases.