Basement membrane (BM) and myoepithelial cells (MEC) in various breast lesions
| Breast lesion | Classification | BM | MEC |
| Microglandular adenosis | Benign but infiltrative | Present | Absent |
| Infiltrating epitheliosis | Benign/focally infiltrative | Mainly present | Focally absent |
| Collagenous spherulosis | Benign | Present | Present |
| Metaplastic apocrine changes | Benign | Present | Can be attenuated or absent in occasional cases. |
| Lactational changes | Benign | Present | Can be attenuated or absent in occasional cases. |
| Ductal carcinoma in situ (DCIS) | Malignant in situ | BM is preserved at the periphery but can be different from the normal BM around the TDLU and breast ducts. | Present but can be focally attenuated. |
| Encapsulated papillary carcinoma | Low grade invasive | Typically, thick capsule-like structure at the periphery. | Absent in 70%–80% of cases at the periphery. |
| Solid papillary carcinoma | Low grade invasive | Typically, thin capsule-like structure (BM) at the periphery. | Absent in 50%–70% of cases at the periphery. |
| Adenoid cystic carcinoma | Malignant invasive | BM-like material at the periphery of the cribriform structures and within the false lumen (pseudocyst). | Absent |
TDLU, terminal duct lobular unit.