Normal histology	Histopathology	Pathological basis of disease	Clinical findings	
•	Each breast consists of 15-25 independent glandular units called breast lobes, each consisting of a compound tubulo-acinar gland.
•	The lobes are embedded in a mass of adipose tissue which is subdivided by collagenous septa.
•	Each breast lobe is divided into a variable number of breast lobules, each lobule consisting of a system of ducts, the alveolar ducts, from which large numbers of secretory alveoli develop during pregnancy.
•	The duct system is lined by cuboidal or low columnar epithelial cells with oval nuclei & prominent nucleoli.
•	A discontinuous layer of plump myoepithelial cells with unstained cytoplasm surrounds the ductal lining cells. 	Abnormal histology:
•	The presence of normal breast elements, i.e. ductal tissue, within a fibroadipose stroma.
•	The nodule is well circumscribed by a condensation of connective tissue & is composed of both epithelial & fibrous stroma components.
•	The nodule is ‘encapsulated’ by a pseudocapsule formed as a result of compression of the surrounding breast tissue by the lesion.
•	The epithelial components form glandular structures lined by mammary duct-type epithelium, whilst the stromal component is a loose, cellular form of fibrous tissue.
•	The nodule exhibits cellular proliferation & is composed of 2 elements, i.e. a mixed tumor.

Fibrous stromal component:
•	Stroma consists of pale staining loose fibroblastic tissue.
•	Stromal cells exhibit no evidence of cellular atypia.

Glandular epithelial component:
•	Presence of glandular ducts of variable sizes.
•	Ducts are lined by cuboidal epithelial cells, either singly or doubly layered.
•	Beneath the epithelial cells are myoepithelial cells.
•	Basement membrane of the ducts are intact.
•	Epithelial cells are benign & do not exhibit cellular atypia or anaplasia.

Pericanalicular stromal proliferation:
•	Fibrous stroma proliferates around the glandular ducts.
•	There is no compression upon the glandular ducts.
•	Ducts appear round or ovoid in shape with patent lumen.

Intracanalicular stromal proliferation:
•	Fibrous stroma proliferates into the glandular ducts.
•	There is compression of the glandular ducts.
•	Ductal lumen are obliterated & the ducts become slit-like structures.	Incidence:
•	Most common benign tumor of the female breast.
•	Occur most often during the reproductive period.
•	Some appear after cyclosporine therapy.
	•	Present clinically as well-circumscribed palpable masses or ovoid mammographic densities.
•	During pregnancy, fibroadenomas may grow in size & sometimes infarct.
•	In older women, fibroadenomas may calcify & present as a cluster of mammographic calcifications.
•	Associated with proliferative changes & incur a slightly increased risk of cancer.