Lung Adenocarcinoma Presenting With Elevated Serum Carbohydrate Antigen 19-9 Levels: A Case Report

Carbohydrate antigen 19-9 (CA 19-9) is a tumor marker usually used for the diagnosis and follow-up of pancreatic, gastric, and hepatobiliary malignancies. However, it has a low specificity and can be elevated in a wide array of other conditions. CA 19-9 elevation in lung tumors seems to be associated with the worst prognosis, but its role in this condition is not fully established yet. We present the case of a 78-year-old woman with mild consumptive symptoms, consisting of unselective anorexia and weight loss, and isolated high levels of CA 19-9. Hepatobiliary and gastrointestinal lesions were excluded, and a suspicious lesion was found in the right lung. A biopsy, which was only possible several months after presentation due to the location and small dimensions of the lesion, confirmed the diagnosis of lung adenocarcinoma. After an initial indolent course, the patient evolved with disease progression and is currently under treatment with palliative chemotherapy. This case illustrates the thorough investigation performed to clarify the elevation of a tumor biomarker measured in a pauci-symptomatic patient, which led to the identification of a rare and unsuspected etiology of high levels of CA 19-9.