Breast cancer is rare in your 20s or 30s, accounting for less than 5 percent of all cases, but it’s the most common cancer for women in this age group.

Younger women with breast cancer experience unique challenges. For women under 40, breast cancer is often diagnosed in its later stages, when it tends to be more aggressive. This means the survival rate is lower and the recurrence rate is higher.

Knowing the risk factors for breast cancer and early signs and symptoms can help you get started on treatment sooner.

Here are some of the most important statistics to know when it comes to breast cancer at a young age.

Breast cancer isn’t common in women under 40.

A woman’s risk of breast cancer throughout her 30s is just 1 in 227, or about 0.4 percent. By age 40 to 50, the risk is roughly 1 in 68, or about 1.5 percent. From age 60 to 70, the chance increases to 1 in 28, or 3.6 percent.

Out of all types of cancer, though, breast cancer is the most common among U.S. women. A woman’s risk of developing breast cancer during her lifetime is about 12 percent.

Some women are at an increased risk of being diagnosed with breast cancer in their 20s or 30s. These risk factors include:

  • having a close family member (mother, sister, or aunt) who was diagnosed with breast cancer before age 50
  • having a close male blood relative with breast cancer
  • having a BRCA1 or BRCA2 gene mutation
  • having received radiation treatment to the chest or breast before age 30

Other risk factors that apply to women of any age include:

  • having a high percentage of breast tissue that appears dense on a mammogram
  • having had a previous abnormal breast biopsy
  • having had your first menstrual period before age 12
  • having your first full-term pregnancy after age 30
  • never having a full-term pregnancy
  • being physically inactive or overweight
  • being of Ashkenazi Jewish heritage
  • drinking excessive amounts of alcohol

Breast cancer happens when cells in the breast begin to grow and multiply abnormally. Changes in DNA can cause normal breast cells to become abnormal.

The exact reason why normal cells turn into cancer is unclear, but researchers know that hormones, environmental factors, and genetics each play a role.

Roughly 5 to 10 percent of breast cancers are linked to inherited gene mutations. The most well-known are breast cancer gene 1 (BRCA1) and breast cancer gene 2 (BRCA2). If you have a family history of breast or ovarian cancer, your doctor may suggest testing your blood for these specific mutations.

Breast cancer in your 20s and 30s has been found to differ biologically in some cases from the cancers found in older women. For example, younger women are more likely to be diagnosed with triple negative and HER2-positive breast cancers than older women.

Here are some statistics about breast cancer in women under 40:

  • About 12,000 women younger than 40 are expected to be diagnosed with breast cancer each year.
  • About 800 women younger than 40 are diagnosed with metastatic breast cancer each year.
  • About 30 percent or more of breast cancer diagnoses occur in the few years after a woman has had a baby.
  • Women younger than 50 are more likely to be diagnosed with triple-negative breast cancer (TNBC). TNBC is cancer that tests negative for progesterone and estrogen receptors and too much HER2 protein. TNBC has lower survival rates.
  • The number of metastatic breast cancer cases diagnosed in women ages 25 to 39 increased by 2.1 percent per year from 1976 to 2009.
  • Survival rates are lower for women younger than 40. According to one study, women age 40 or younger were 30 percent more likely to die from breast cancer compared to women who were diagnosed between the ages of 51 to 60.
  • Almost 1,000 U.S. women younger than 40 died from breast cancer in 2017.

The number of women under 40 being diagnosed with metastatic breast cancer is increasing.

Metastatic breast cancer means that the cancer has advanced to stage 4 and has moved beyond the breast tissue into other areas of the body, such as the bones or the brain. Survival rates are lower for cancer that has metastasized to other parts of the body.

According to the American Cancer Society (ACS), the 5-year survival rate for those with breast cancer that has spread to other parts of the body is 27 percent for women of all ages. However, one study found no significant differences in median survival rate between younger and older women with metastatic breast cancer.

Another study looked at more than 20,000 women diagnosed with stage 4 breast cancer between 1988 and 2011. The data suggests that survival rates have been improving since the late 80s and early 90s.

It’s often difficult for doctors to diagnose breast cancer in women under 40 because younger women have denser breasts. A tumor won’t typically show up as well on mammograms in younger women.

So, one significant sign of breast cancer is a change or lump in the breast area. The majority of young women diagnosed with breast cancer discover an abnormality themselves.

Always report any breast changes, including changes in the skin, nipple discharge, pain, tenderness, or a lump or mass in the breast or underarm area, to your doctor.

Breast cancer is uncommon in your 20s and 30s, but it can still happen. Routine screening isn’t recommended for this age group, so diagnosis can be difficult. Understanding the statistics, as well as your personal risk factors, can help with early diagnosis and treatment.