Cancer antigen 125 (also known as carbohydrate antigen 125 or CA 125) is an antigen first identified by Bast et al. Although much research has been done to understand the molecular structure of CA 125, its function remains a source of much speculation. At present, CA 125 is most commonly used in the diagnosis of epithelial non-mucinous ovarian cancers, and in monitoring their response to treatment. Following surgical resection, CA 125 levels are expected to half within 10 days and it is therefore a useful tool for assessing response to treatment as well. We present a case of incidental finding of rasied CA125, followed by the literature review to discuss a better understanding of the factors that lead to CA 125 production, its mechanisms of action, and the nature and functions of its subspecies may help in improving its use as a standalone diagnostic tool.

Carbohydrate antigen 125 (CA125) is an antigen used in the diagnosis of epithelial nonmucinous ovarian cancers. CA125 may be elevated in many benign and malignant conditions, so elevated levels can cause confusion over patient management. The multidisciplinary team is important when planning care for patients with suspected ovarian cancer. Learning objectivesTo know the factors leading to CA125 production and its mechanism of action.To understand how CA125 is used as a diagnostic tool and to assess the treatment response of ovarian cancer. To appreciate patient care options in cases of falsely elevated CA125. Ethical issuesIs the CA125 blood test being used in patients appropriately and safely? In patients with elevated CA125 levels, does this lead to unnecessary investigations and invasive treatments? Keywords: CA125 / gynaecological causes of raised CA125 / nongynaecological causes of raised CA125 / ovarian cancer / ovarian cancer follow-up