Worldwide, breast cancer is the most often diagnosed life-threatening disease in women. It is the second leading cause of cancer death in women after lung cancer. More than one million new cases of breast cancer are diagnosed every year globally and more than 400,000 deaths occur due to this pathology. Male breast cancer accounts for <1% of total cases; in men, symptoms, diagnosis, and management are the same.
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Breast cancer most frequently involves glandular breast cells in the ducts or lobules. Breast cancer has four types and it may be either invasive or noninvasive. There are two types of noninvasive breast cancers: ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS). These two types of noninvasive breast cancers do not invade the basement membrane of the breast. As the names suggest ductal carcinoma in situ cancer cells are found in the lining of the duct whereas lobular carcinoma in situ cancer cells are found in the lobules.
There are also two types of invasive breast cancer: infiltrating ductal carcinoma and infiltrating lobular carcinoma. Infiltrating ductal carcinoma go through the wall of the duct and move to areas outside of it whereas infiltrating lobular carcinoma spreads through the wall of the lobule and also travels to areas outside of it. Infiltrating ductal carcinoma is the most common type of breast cancer, accounting for between 70%-80% of the cases of breast cancer.
Pathophysiology of Breast Cancer
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What makes a Normal Cell Turn Cancerous?
There are trillions of cells in the body having regulated cell cycle that controls their growth, maturity, division and death. During childhood normal cells divide faster to allow the person to grow. In adulthood the cells divide to replace worn-out cells and to repair injuries. This cell division and growth is controlled by DNA and genes that lie within the cell’s nucleus.
Cancer begins when cells in a part of the body start to grow out of control. All types of cancer, irrespective of their origin, occur due to this disturbed growth of cells that leads to formation of tumors and lesions.
A normal cell can become a cancer cell if it undergoes damage to the DNA. It is the DNA that regulates the cycle of growth and death and any changes or damage of the cell.
For most cells if the DNA is damaged the cell either repairs the damage or the cell dies. In cancer cells, the damaged DNA is not repaired and the damage is spread to new abnormal cells that are born of the defective cell. Damaged DNA by mutation can also be inherited or can also occur due to exposure to toxins like cigarette smoking, alcohol etc.
The Cancerous Breast
Breast cancer is a malignant tumor where cells in the breast tissue grow and divide abnormally. Commonly breast cancer develops from the epithelial lining of the ducts or from the epithelium of the lobules. Angiogenesis happen for growth of malignant breast cells. Angiogenesis is the physiological process through which new blood vessels form pre-existing vessels. These new blood vessels provide nutrients for growing cancerous cells.
As the malignant tumor matures, it can spread into adjacent cells and tissues. This process is called invasion. Cancerous cells are also able to break away and move from the primary tumor and spread to other common sites like bone, liver, lung, and brain.
Breast Cancer Pathophysiology
Like other cancers, there are several factors that can raise the risk of getting breast cancer. A variety of factors, both genetic and environmental, may disrupt normal growth regulatory pathways resulting in the development of cancer. Endogenous as well as exogenous hormone exposure, ionizing radiation exposure, and genetic mutations in DNA repair genes are among the more well-known factors contributing to breast cancer development.
Damage to the DNA and genetic mutations can lead to breast cancer have been experimentally linked to estrogen exposure. Estrogen and progesterone are important regulators of normal breast growth and development as well as breast involution and play important roles in the pathogenesis of breast cancer. Estrogen and progesterone receptors, present in some breast cancers, are nuclear hormone receptors that promote DNA replication and cell division when the appropriate hormones bind to them. Thus, drugs that block these receptors may be useful in treating tumors with the receptors.
About two thirds of postmenopausal patients have an estrogen -receptor positive (ER+) tumor. Incidence of ER+ tumors is lower among premenopausal patients. Some individuals inherit defects in the DNA and genes like the BRCA1, BRCA2 and P53 among others. Another cellular receptor is human epidermal growth factor receptor 2 (HER2; also called HER2/neu or ErbB2); its presence correlates with a poorer prognosis at any given stage of cancer. Breast cancer invades locally and spreads through the regional lymph nodes, bloodstream, or both.
Metastatic breast cancer may affect almost any organ in the body. Most metastases occur near the site of breast surgery. Most patients are diagnosed with an asymptomatic mass discovered during examination or mammography. Diagnosis is confirmed by biopsy. Treatment of breast cancer includes surgical excision, often with radiation therapy, with or without adjuvant chemotherapy, hormonal therapy, or both.