Like most diseases, cancer risk increases with age. This is due to the fact that increasing time allows for cell mutations to accumulate and environmental factors to interact with genetics. Abnormal growth of cells results in a mass called a tumor. Benign tumors do not invade other tissues and are not truly cancerous. Malignant tumors spread to other tissues (metastasize). Cancerous cells impair function of tissue and thus can cause death. Abnormal growth of cells results from disruption of normal cell division, usually occurring due to a series of events over time that alter the cell division process. Typically, multiple mutations combine to affect cell growth. This can be a combination of inherited and acquired genetic effects, as well as environmental interaction.
There are three primary types of genetic changes associated with cancer. Oncogenes are mutated forms of normal genes called proto-oncogenes that are involved in regulation of cell growth pathways. Oncogenes alter the expression or activity of proto-oncogene proteins. Oncogenes alter pathways resulting in over-activation of cell growth and survival.
Tumor suppressor genes function in various ways to prevent uncontrolled cell growth. Tumors will develop if tumor suppressor genes are inactivated.
Mistakes in the genetic code occur frequently. Studies have shown that even with a 99.99% level of accuracy in DNA copying, a person will have one coding mistake every 10,000 bases. Genes are typically several kilobases, so mistakes are common. DNA repair genes have enzymes that correct mistakes in genetic code due to copying errors and damage (such as from UV radiation). Genetic mutations linked to cancer are most commonly associated with proto-oncogenes, tumor suppression, and DNA repair, but many other types of genes are also linked to cancer.
Breast cancer is one of the primary causes of death in the United States. Estimated new cases from breast cancer in the US during 2014 are 232,670 females and 2,360 males. Deaths from breast cancer in the US in 2014 were about 40,000 females and 450 males. The lifetime risk of breast cancer for women is 1 in 8 (about 12%) and 1 per 1,000 in men. The risk of the cancer is substantially higher in many families with a history of the disease.
There are several different types of breast cancer that each has unique characteristics in regards to pathology, risk of death, and responsiveness to treatment.
Each breast is made up of 15 to 20 sections called lobes. Each love consists of many lobules, which terminate in dozens of bulbs. Ducts connect the lobes, lobules, and bulbs. Breasts also contain lymph vessels and nodes, which have significant roles in immune function.
Breast cancer can either develop in the ducts, called ductal carcinoma or in the lobules, called lobular carcinoma. Both types of cancer can be localized in their respective tissue type and non-invading—meaning, they are in situ (“in place”). Both types of cancer can also spread beyond their respective tissue type—called invasive. Therefore, there are four major categories of breast cancer: ductal carcinoma in situ and invasive ductal carcinoma, lobular carcinoma in situ and invasive lobular carcinoma.
Of these types, the in situ types are the least serious. Ductal carcinoma in situ can be removed by lumpectomy, but lobular carcinoma in situ require mastectomy. In situ cancers are not immediately dangerous, but are associated with increased risk of invasive cancer and mortality.
In situ ductal carcinomas can develop into invasive carcinomas, which is not common for lobular carcinomas. In situ ductal carcinoma is associated with invasive carcinoma in the same breast. 80% of all breast cancer is invasive ductal carcinoma. Invasive carcinomas can spread into the lymph system, which facilitates metastasis. Metastasis causes the spread of cancer and poor prognosis.