1. New Oxford American Dictionary: 2010, 2013 by Oxford University Press, Inc
2. Foulds L. Multiple etiologic factors in neoplastic development. Cancer Res. 1965;25(8):1339–47.
3. Weinberg RA. The biology of cancer, Second edition. New York; London: Garland Science; 2014.
4. Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P. Molecular Biology of the Cell. New York: Garland; 2014.
5. Foulds L. Tumor progression: a review. Cancer Res. 1954;14:327–39.