MUC16 and gastric cancer: However, several physiological and non-physiological factors affect normal serum CA125 levels, including premenopause, pregnancy (35), menstruation, smoking (34), old age, endometriosis (36), and several malignant conditions, such as breast cancer (37), mesothelioma (38), gastric cancer (39), non-Hodgkin’s lymphoma (40), heart failure (41), and liver cirrhosis (42).