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Breast Cancer Module I: Breast Anatomy, Physiology, and Pathology

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Target Audience and Goal Statement

This activity is intended for primary care providers who perform screening and clinical breast exams.

The goal of this activity is to enable primary care providers to better understand the anatomy, physiology, and pathology of the breast.

Upon completion of this activity, participants will be able to:

  • Identify the normal anatomy and physiology of the breast
  • Distinguish abnormal clinical and pathology findings of the breast
  • Define the major types of benign and malignant breast lesions and their prognostic significance

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Breast Cancer Module I: Breast Anatomy, Physiology, and Pathology


Microscopic Anatomy

The distal terminus of the ductal network is the terminal ductal lobular unit (TDLU). Each of the lobes in the breast contains thousands of TDLUs, which form the functional secretory unit. The secretory units produce milk, which drains via the branching ducts to their terminus as the ampullae at the surface of the nipple. The TDLU is complex and consists of the extralobular and intralobular terminal ducts, and the blindly ending lobules (or ductules). An inner layer of secretory cells and an outer layer of myoepithelial cells which contain contractile fibers that eject the milk into the ducts during lactation surround this inner layer. Hence the lobules are referred to as acini during pregnancy and lactation.

Lymphatic Drainage and Blood Supply

Most of the lymphatic drainage of the breast is into the axilla, although the lower inner quadrants drain to the infraclavicular and sometimes to the medial substernal nodes. The lymphatic channels travel through the axilla, along the sternum, and above and below the clavicle. Arterial blood supply is abundant, while the venous drainage is variable. Most major venous pathways lead to the pulmonary capillary network (why lung metastases are common) or the vertebral veins (skeletal metastases). Obstruction of the lymphatic system in the dermis of the skin is a serious sign of inflammatory carcinoma of the breast. Later-stage presentation will give the skin an orange peel appearance called "peau d'orange."