Anatomy, Physiology & Disease Process

Normal Anatomy & Physiology of the Breast

The breast is made up of several main structures. Lobules are glands that can produce milk. Ducts are small tubes that carry milk toward the nipple. The breast also contains fatty tissue, connective tissue, blood vessels, lymph vessels, and nerves. In a healthy body, breast cells grow, divide, and die in a controlled way — the balance that keeps tissue healthy and organized.^[1]

The HER2 Protein

HER2 stands for human epidermal growth factor receptor 2 — a receptor protein on the surface of some cells. Receptors help cells receive signals; in normal tissue, growth signals help cells repair and replace themselves when needed.^[2]

In HER2-positive breast cancer, the cells have too much HER2, sending too many growth signals. The result is faster cell division and more aggressive tumor growth. About 15–20% of breast tumors are HER2-positive.^[2]

"The cancer was extremely aggressive — described as a cell eater." — Interview Subject

How the Disease Disrupts Normal Physiology

Cancer begins when abnormal cells grow out of control. In metastatic breast cancer, some cancer cells break away from the original tumor, travel through the blood or lymph system, and form new tumors in distant parts of the body. Even after spreading, it is still considered breast cancer — for example, breast cancer that spreads to bone is called metastatic breast cancer to the bone, not bone cancer.^[1]

Stage 4 disease disrupts the body in several ways:

• • Bone — weakens the skeleton; pain or fractures.
• • Lungs — interferes with breathing.
• • Liver — affects liver function; jaundice or swelling.
• • Brain — headaches, seizures, dizziness, speech or vision changes.^[1]

Because HER2-positive tumors grow and spread faster than HER2-negative tumors, the disease can be especially aggressive without effective treatment. HER2-targeted therapies are designed to block this pathway and slow or stop cancer growth.^[2]