FACTBOX — What is lung adenocarcinoma, the cancer diagnosed in Pope Leo?

VATICAN CITY, Oct 14 (Reuters) — Pope Leo was diagnosed with lung adenocarcinoma after doctors removed the lower lobe of his right lung during surgery on Tuesday, the Vatican said. Here are some facts about the disease. What Is It? Adenocarcinoma is a type of cancer that forms in glandular cells, which produce substances such as mucus. In the lungs, it develops in cells lining the air sacs and is the most common subtype of non-small cell lung cancer (NSCLC), the category that accounts for about 80%-85% of lung cancers. Adenocarcinoma represents roughly 40% of all lung cancer cases, according to the Lung Cancer Foundation of America. It is typically found in the outer parts of the lungs and tends to grow more slowly than some other forms of lung cancer, increasing the chances of detection before it has spread. Who Gets It? Smoking remains the main risk factor. However, adenocarcinoma is also the most common type of lung cancer among people who have never smoked. The pope is not known to have been a smoker. Symptoms Early-stage disease often causes no symptoms and may be discovered during scans performed for other reasons. As the cancer progresses, symptoms can include a persistent c