Another case of colloid adenocarcinoma of the lung. The image shows mucin rich matrix created by dissecting pools of mucin which destroy the native lung architecture. The tumor elements consist of extremely well-differentiated tall columnar cells lining the alveolar septa in a lepidic pattern. Mitotic activity is low and necrosis is not present. Immunohistochemically, the colloid adenocarcinomas of the lung express intestinal markers such as CDX2, MUC2, and CK20. Napsin A may be positive. TTF1 and CK7 are usually negative or show weak focal positivity.