MUC5AC and neoplasm: It recognizes the following common histologic patterns or subtypes - lepidic (cancer cells growing along but not invading through alveolar walls), acinar (glandular structures invading adjacent stroma), papillary (branching structures of fibrovascular stroma covered by invasive cancer cells), solid (sheets or nests of cancer cells containing cytoplasmic mucin) and the newly added micropapillary subtype (papillary tufts of tumor cells without fibrovascular cores either lying apparently free in alveolar spaces or surrounded by thin fibrous septa, often at a tumor's edge).