GÜLŞEN, Mustafa, et al. “CARCINOEMBRYONIC ANTIGEN (CEA) LEVELS IN BLOOD SERUM AND GASTRIC JUICE IN BENIGN AND MALIGNANT GASTRIC LESIONS”. Turkish Journal of Gastroenterology, vol. 5, no. 1, Apr. 2020, pp. 68-71, https://turkjgastroenterol.avesjournals.com/index.php/tjg/article/view/261.