M. K. TÜRKDOĞAN, H. TESTERECİ, T. KAHRAMAN, İlyas TUNCER, E. ALGÜN, and İbrahim H. YÖRÜK, “Serum and tissue levels of vitamin A and E gastric and esophageal cancer”, Turkish Journal of Gastroenterology, vol. 7, no. 4, pp. 327–330, Jan. 1996.