Adenocarcinoma is a type of cancer that originates in glandular epithelial cells, which are responsible for secreting substances, and it can develop in many parts of the body. It is the malignant counterpart to a benign adenoma, and while some adenomas can transform into adenocarcinomas, most do not. This cancer is particularly prevalent in the breast, colon, pancreas, and prostate—for instance, over 80% of pancreatic cancers and nearly all prostate cancers are adenocarcinomas. In the colon, researchers like Vogelstein have mapped a genetic progression where cells lose the APC tumor suppressor gene, then activate k-Ras, leading to a benign polyp that can eventually become an invasive malignancy. Pathologists diagnose adenocarcinomas by staining biopsy cells to identify their glandular characteristics, though the tumors can vary greatly in severity and appearance depending on how well-differentiated they are. Notably, while most cervical cancers are squamous cell carcinomas, about 10–15% are adenocarcinomas, and in the developed world, esophageal cancer is most commonly of this type.