Breast Anatomy

The breast sits on the anterior chest wall between the 2nd and 6th ribs. It's divided into four quadrants — the upper outer quadrant is the most common site for breast cancer. The nipple-areola complex is central. The tail of Spence extends into the axilla and is clinically important because pathology here can mimic axillary lymphadenopathy.

In terms of histological origin, the majority arise from the ductal epithelium (invasive ductal carcinoma, ~70-80%), with lobular carcinoma being the next most common (~10-15%).

The breast has glandular tissue (15-20 lobes, each with lobules draining into lactiferous ducts), stromal fibrous connective tissue, and adipose tissue. Cooper's ligaments are fibrous septae running through the breast — when cancer invades them, they shorten and cause the classic skin retraction and dimpling (peau d'orange). This is a key clinical sign of malignancy.

Blood supply comes from the internal mammary (medial), lateral thoracic (lateral), thoracoacromial (superior), and intercostal arteries (posterior). Lymphatic drainage is critical for cancer staging: axillary nodes (levels I-III) are the primary route, internal mammary nodes drain medial tumours, and supraclavicular involvement indicates advanced disease. This is why sentinel lymph node biopsy is a key part of cancer surgery. Axillary Nodes Axillary Nerves Terminal Duct-Lobular Unit