How Does Breast Cancer Start?

Medically Reviewed on 6/3/2022
Breast cancer develops in the cells of the breasts and can spread to other parts of the body (metastasis).
Breast cancer develops in the cells of the breasts and can spread to other parts of the body (metastasis).

Breast cancer develops in the cells of the breasts and can spread to other parts of the body (metastasis). It is one of the most common cancers diagnosed in women in the US. Although extremely rare, breast cancer can sometimes occur in men.

Breast cancer forms when there are changes or mutations in the deoxyribonucleic acid (DNA), which can cause normal breast cells to become cancerous. Some DNA changes are inherited (passed on in families), whereas others may be associated with other risk factors.

Researchers have found that several factors can increase the risk of breast cancer. It could either be a single risk factor or a combination of risk factors that cause breast cancer.

A spontaneous or inherited change in the DNA is the trigger for cancerous cells to multiply and form a tumor.

Risk factors for breast cancer

Some common risk factors that have been identified to cause breast cancer are as follows.

  • Genetic factors: A family history of breast cancer increases the risk of the disease. Breast cancers may occur due to the inheritance of mutated genes. The most affected genes causing breast cancer are BRAC1 and BRAC2. They also increase the risk of ovarian cancer.
  • Age: The risk of breast cancer increases with age. Most women with breast cancer are older than 50 years of age, though a few cases may be seen in younger women.
  • Radiation exposure: This could be due to occupational exposure, imaging, or radiotherapy for other conditions to the chest during childhood.
  • Early menarche: This is the onset of periods before the age of 12 years. 
  • Late menopause: Onset of menopause after the age of 55 years.
  • Late first pregnancy: Being pregnant after the age of 30 years or never getting pregnant.
  • Hormone replacement therapy: Hormonal therapy to reduce the side effects of menopause or for other reasons increases breast cancer risk.
  • Lifestyle factors: Smoking, excessive alcohol consumption, obesity.


Breast Cancer Awareness: Symptoms, Diagnosis, and Treatment See Slideshow

What are the signs and symptoms of breast cancer?

In the early stages, there may be no noticeable symptoms of breast cancer.

Common signs and symptoms include:

  • A painless lump in the breast or under the armpit. The lump is firm or hard and does not move within the breast tissue (fixed to the underlying structures). Self-examination by patients and regular screening in high-risk individuals are advised. This allows for early diagnosis and treatment.
  • In some people, there can be swelling throughout the breast or in part of the breast without a palpable lump.
  • Cancer cells multiply fast and spread quickly. Hence, the lump quickly increases in size, involves surrounding structures (including the skin), and spreads to the rest of the body.
  • The affected skin of the breast appears reddish and dimpled similar to that of an orange peel.
  • Changes in the breast shape.
  • The nipple, if involved, may become retracted, leading to an inverted appearance.
  • Discharge or bleeding from the nipple.
  • Peeling, crusting, and flaking of the areola (pigmented skin around the nipple) or the skin of the breast.
  • Enlarged lymph nodes felt as lumps in the armpit, groin, neck, and other areas.

What are types of breast cancer?

There are several types of breast cancer, and they are broken into two main categories.

  1. Noninvasive breast cancer
    • Noninvasive cancer is also termed carcinoma in situ or precancers. This form of cancer is contained within the milk ducts or lobules in the breast but has not grown or invaded the normal breast tissue. There are two main forms of noninvasive breast cancer:
      • Ductal carcinoma in situ (DCIS)
      • Lobular carcinoma in situ (LCIS)
  2. Invasive breast cancer
    • Invasive breast cancer is a type of cancer that has spread into the surrounding tissues outside the ducts and lobules. Most breast cancers are invasive, but there are different types of invasive breast cancers, they include:

Subtypes of breast cancer

Three main subtypes of breast cancer include:

  1. Hormone receptor-positive breast cancer: These are cancer cells that need female hormones (estrogen and progesterone) to grow and reproduce. About 80 percent of all breast cancers are estrogen positive and 65 percent are progesterone positive.
  2. HER2-positive breast cancer: This breast cancer has an excessive amount of the protein called human epidermal growth factor receptor 2 on the surface of the cells. The excess HER2 receptors promote the growth of the cancer cells.
  3. Triple-negative breast cancer: This is another rare type of breast cancer that lacks all three receptors (estrogen, progesterone, and HER2), which are commonly found in breast cancer cells. This type of cancer tends to grow and spread more quickly than other types of breast cancers.

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Medically Reviewed on 6/3/2022
References Metastatic Breast Cancer.

Chalasani P. Breast Cancer. Medscape.