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:
•	Presence of normal breast ductal tissue within a fibroadipose stroma.
•	Fibrocystic changes: there are cystically dilated ducts, areas of lobules that are laced with abundant fibrous connective tissue.
•	The glandular ducts of the breast are dilated to form cysts of variable sizes.
•	The cysts are lined by a single epithelial layer of varying height.
•	In the markedly dilated ducts, the lining epithelial cells exhibit signs of atrophy.
•	The epithelial cells of some ductal cysts have undergone apocrine metaplasia:

Apocrine changes:
•	These cystic glandular structures have the appearance of apocrine sweat ducts.
•	The lining epithelium consists of a single layer of columnar cells with abundant granular eosinophili cytoplasm, prominent basal-central nuclei, & resting upon an intact basement membrane.
•	The lining epithelial cells exhibit no features of cellular atypia or anaplasia.
•	The epithelial lining may exhibit papillary proliferation into the ducts, i.e. papillary infoldings.	Pathological features:
•	Cyst formation
•	Apocrine metaplasia
•	Adenosis
•	Fibrosis

Incidence:
•	Most common between ages 20-40.
•	Unusual before adolescence.
•	Peak in perimenopausal years.
•	Rarely develop after menopause.

Rupture of cyst:
•	Release secretory debris into stroma resulting in inflammation & fibrosis.
•	Contributes to palpable firmness of breast.
•	Adenosis: an increase in the number of acini per lobule.
•	The acini often become dilated & may contain calcifications.	•	Do not increase risk of developing cancer in the absence of proliferative breast disease.
•	Mimic cancer by producing palpable lumps, mammorgraphic densities, calcification or nipple discharge.
•	Account for half of all surgical operations on the breast.