MUC5AC and lung adenocarcinoma: Lung adenocarcinoma: Five invasive tumor patterns, or variable combinations, may be identified: Adenocarcinoma with lepidic growth, cells proliferating in the surface of the alveolar walls without stromal or vascular invasion,29 the papillary pattern in which papilar structures replaces the alveolar architecture,30 or the micropapillary arrangement with micro-papillae without a fibrovascular core, and the solid type with mucin.31