Breast cancer is a common cancer, but experts are still not sure why this might be. However, researchers have identified certain risk factors for breast cancer, such as physical inactivity and having obesity.

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Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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The majority of breast cancers start in the cells of glandular tissue in the breast. It is the second most common type of cancer worldwide.

This article examines why breast cancer is so common. It also looks at the prevalence of breast cancer and risk factors a person can control.

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Experts are still unsure why breast cancer is so common, but they do know of certain factors that increase the risk of breast cancer. Being female is the most significant risk factor for breast cancer.

The American Cancer Society (ACS) notes that hormones may play a role in the development of breast cancer. And breast cancer may be more common in females due to the hormonal stimulation of breast cells, which are highly responsive in females.

When breasts are fully formed, the breast cells are immature and very active until a person goes through a full-term pregnancy. Immature breast cells are responsive to hormones such as estrogen. The increased responsiveness of female breast cells to hormones increases the risk of developing breast cancer.

Males do not typically develop fully-formed breasts, and they usually consist of fat. The breast cells are inactive, and most males have low levels of estrogen.

Age is the second biggest risk factor for breast cancer. Breast cancer occurrence increases with age and peaks at menopause. Beginning menopause after the age of 55 years may increase exposure to estrogen, which may increase the risk of breast cancer.

Gene mutations can also lead to breast cancer. The ACS reports that around 10% of breast cancers may be due to abnormal genes that people have inherited, while roughly 90% occur due to acquired mutations. The reason for acquired genetic mutations is not always clear.

According to a 2022 article, risk factors for breast cancer worldwide include:

  • experiencing menopause at a later age
  • undergoing hormone replacement therapy
  • using hormonal contraception containing estrogen long term
  • getting married at a later age
  • having the first childbirth at a later age
  • having a late-night work schedule
  • eating a nonvegetarian diet high in animal fat
  • not getting enough physical activity
  • having obesity
  • lacking the proper awareness or screening
  • receiving a delayed diagnosis
  • not having access to sufficient healthcare facilities

Alcohol intake is also a risk factor for breast cancer. Moderate alcohol consumption of more than 35–44 grams per day, or about three or four standard drinks, increases the risk of breast cancer by 46%. According to the ACS, reducing alcohol consumption directly lowers a person’s risk of breast cancer.

The ACS reports that breast cancer is the most common type of cancer affecting females in the United States, not including skin cancers. It accounts for 1 in 3 of all cancers that develop in females per year.

The ACS estimates that in 2022, there will be around 287,850 new cases of invasive breast cancer diagnoses in the U.S.

Breast cancer mostly affects females with a median age of 60–62 years at the time of diagnosis. Fewer females are diagnosed with breast cancer under the age of 45 years.

Among females under the age of 40 years, Black females have a higher risk of developing breast cancer than white females.

According to the World Health Organization (WHO), 2.3 million females received a diagnosis of breast cancer worldwide. Around 0.5 to 1% of breast cancers occur in males.

Risk factors for breast cancer that people may be able to control include:

  • not being physically active
  • having obesity or being overweight after menopause
  • taking hormone replacement therapy for more than 5 years
  • taking certain hormonal contraceptive pills
  • having a first pregnancy after the age of 30 years
  • not breastfeeding
  • never having a full-term pregnancy
  • drinking alcohol
  • smoking
  • working night shifts, which may cause hormone changes

Risk factors for breast cancer that are outside of people’s control include:

  • being of older age
  • having a genetic mutation
  • starting menstrual periods before the age of 12 years
  • starting menopause after the age of 55 years
  • having dense breasts
  • having had breast cancer previously
  • having certain noncancerous breast diseases
  • having a family history of breast cancer or ovarian cancer
  • having previous radiation therapy to the chest before the age of 30 years
  • receiving exposure to the drug diethylstilbestrol (DES)

Although there is no definite way to prevent breast cancer, people may be able to lower their risk by taking steps such as:

  • reaching and maintaining a moderate weight
  • staying physically active
  • aiming for at least 150–300 minutes of moderate-intensity exercise, or 75–150 minutes of vigorous-intensity exercise, every week
  • avoiding or limiting alcohol, and avoiding drinking more than one alcoholic drink per day (for females)
  • eating a healthy diet with plenty of fruits and vegetables that is low in fat, red and processed meat, and added sugars
  • considering nonhormonal contraceptive or menopausal treatment options

Additionally, for people who give birth, breastfeeding for several months or more after childbirth may help reduce breast cancer risk.

If people have an increased risk of breast cancer due to genetics or family history, they may want to consider:

  • seeking genetic counseling and testing
  • taking medications to reduce breast cancer risk
  • undergoing preventive surgery
  • receiving close observation to check for early signs of breast cancer

Breast cancer is one of the most common cancers and is the second most common cancer that affects females.

Treatment for breast cancer is highly effective and may lead to survival rates of 90% or above, especially when people receive an early diagnosis.

If people notice any symptoms of breast cancer or unusual changes to the breasts, they can contact a doctor for a checkup.

In many cases, an abnormal sign, such as a lump, is noncancerous and could indicate a cyst or infection, but it is important to find out the underlying cause.