Differential diagnosis of blunt duct adenosis (BDA) vs columnar cell lesion (CCL) with and without atypia
| CCL without atypia | CCL with atypia | BDA | |
| Shape of acini/ducts | Round to oval | Round to oval | Distended, irregular, tubular |
| Architecture | Flat, tufts or mounds | Flat, tufts or mounds; no well-formed bridges and papillary structures | Flat, tufts or mounds |
| Stratification | Present in CCL with hyperplasia | May be present | Mild stratification may be present, sometimes (minimal) hyperplasia |
| Conspicuous cell borders | + | + | – |
| Luminal snouting | + | + | + |
| Intracytoplasmic vacuoles | Rare | Rare | – |
| Dimorphic cell population (‘pale cells’) | Rare | More frequent | – |
| Myoepithelium | Inconspicuous | Inconspicuous | Conspicuous |
| Overlapping nuclei | – | – | Slightly |
| Nuclear arrangement | Regular | Regular or disorderly | Disorderly |
| Nuclear size | Monotonous, small | Monotonous or variable; enlarged | Slightly variable, slightly to moderately enlarged |
| Nuclear shape | Elongated/oval | Oval to round | Round to oval, slightly irregular |
| Nucleoli | Inconspicuous; small | May be conspicuous | Small to prominent |
| Position of nuclei | Basal | Usually central | Basal |
| Microcalcifications | + | + | + |
| Luminal secretion | + | + | + |
| Luminal mucin | Rare | Rare | – |
| Intralobular stroma | Normal | Normal | Expanded and mildly cellular, often myxoid |
| Immunohistochemistry | CK5 negative | CK5 negative | CK5 mosaic in hyperplastic areas |
| Molecular pathology | 16q loss | 16q loss | no 16q loss |
+/–, may be present; +, usually present; –, not present; CK, cytokeratin.