Breast Cancer in Young Women: Rates Rise, Guidelines Shift

5 min read

May 29, 2024 -- Breast cancer does not discriminate based on age. 

Women across the world are increasingly becoming diagnosed with breast cancer under the age of 40.  Researchers from the Washington University School of Medicine in St. Louis found a 20% increase in breast cancer diagnoses among women born in 1990 compared to those born in 1955. Moreover, the types of breast cancer found in women under 40 “tend to have later-stage tumors, when the disease is more advanced and more difficult to treat,” according to Adetunji T. Toriola, MD, PhD, MPH, co-leader of the Cancer Prevention and Control Program at Siteman Cancer Center in St. Louis, MO.

Making matters worse, most women don’t begin regular breast cancer screening until at least age 40. In fact, the U.S. Preventive Services Task Force released new guidelines this month to begin mammograms every other year at age 40, rather than the previous annual exam at 50. 

Such a large shift in the recommended screening age raises the question: What is causing breast cancer in younger women?

There are many factors at play. Some of these include:

  • Exposure to toxins
  • Screening
  • Lack of education in performing self-exams
  • Genetics
  • Race

Toxin Exposure

There are over 2,400 chemicals banned within European cosmetic companies; there are 11 banned in the United States. Because the FDA does not have the authority to require cosmetic companies to submit their safety data, tracking the ingredients list and safety risks is difficult. More than 80,000 chemicals have been introduced into the marketplace in the past 50 years, many of which are known carcinogens. Many of these chemicals are found in items targeted for women. Repeat exposure to these known toxins can increase the risk of breast cancer.

Screening Exams

The lack of screening exams for women under 40 are one of the biggest risk factors for the advancement of breast cancer to a later stage. Insurance policies have made it difficult to access ultrasounds and mammograms for screening purposes for younger women. While these imaging tools should not be the first choice for screening, it should not be difficult to access when a woman suspects a problem or is considered “high risk.” 

Joshua Jarman, MD, a breast radiologist with Saint Alphonsus Health System in Boise, ID, believes that “some of the uptick is actually because of increased screening.”

In a lot of cases, he said, an early-stage cancer called ductal carcinoma in situ “would have smoldered in the breast for a long time without women even knowing.” 

While the increased screening may explain the increase in diagnoses among women, it does not shed a light on what’s causing a higher incidence of aggressive breast cancers.

Lack of Education

The absence of curriculum in health classes that teach students how to perform a breast self-exam is a major component in the lack of detection. Health education classes in many Middle Eastern and African countries have created curriculum that supports breast health education. They instruct the students, both male and female students, how to perform a breast exam and when. In 2009, the U.S. Preventive Services Task Force recommended ending the practice of teaching teen girls in high school how to perform self-exams. The group, whose recommendations health care insurance companies typically follow, found the exams could cause mental health problems and lead to unnecessary biopsies and treatments. 

“For the teaching of [self-exams], there is moderate certainty that the harms outweigh the benefits,” the task force said at the time. 


Genetics play a major role in the development of breast cancer in young women, which is why it is important to ask questions within your family. Younger women diagnosed with breast cancer are typically associated with a genetic link. There are genes called BRCA1 and BRCA2 that can be hereditary among men and women. Johns Hopkins found that BRCA genes may account for a “45-85% chance of developing breast cancer in your lifetime, along with a 10-46% chance of developing ovarian cancer.” Certain cancers within the family can also be related to breast or ovarian cancer, such as:

  • Prostate
  • Salivary gland cancer
  • Colon
  • Pancreatic
  • Esophageal
  • Lung cancer
  • Stomach
  • Uterine
  • Thyroid
  • Melanoma

The closer the relation to a family member – such as your mother or sister -- with these types of cancer, the higher the risk of developing breast cancer. Genetic counseling and testing can be performed with a simple questionnaire and a blood test to determine whether there are genetic mutations. 


Race, unfortunately, also places women at higher risk for breast cancer at younger ages. Research from a 2024 study has found that Black women, especially among those ages 20 to 29, have a 53% increased risk compared with white women of the same age group. A study from 2020 found that Black women are more likely to die from breast cancer than any other ethnic group as well. 

Increased risks for the development of breast cancer are hereditary among eastern European Jews. The CDC has found about 1 in 40 Ashkenazi women carry the BRCA gene, making them more susceptible to developing breast cancer under the age of 50.     

Increased Cases of Hormone-Positive Breast Cancers

There has been an increase in hormone-positive and HER2-positive cancers in the United States. On cancer cells, there may or may not be the presence of hormone receptors. The hormone receptors are referred to as ER (estrogen receptor) and PR (progesterone receptor) and will either be negative or positive when tested. 

These hormone receptors feed off estrogen and progesterone, resulting in cancer cell growth. The hormones do not cause cancer, but they provide nourishment to cancer cells and support growth. 

Younger women have higher levels of these hormones to aid in fertility. When there is an increase in hormone-positive cancers, these hormones fuel the cancer that is going undetected. 

“We also hope to learn from the decrease in estrogen-receptor-negative tumors,” Toriola said. “If we understand what is driving that rate down, perhaps we can apply it in efforts to reduce or prevent other breast tumor types.” 

On a cancer cell, there may or may not be a protein called HER2. There has been an increase in HER2-positive breast cancer cases, which is associated with a more aggressive form of breast cancer. Risk factors for HER2-positive breast cancers include first child born after age 30, having prior radiation to the chest, being less than 30 years old, and having a family history of breast cancer.

A potential contributor to the rising numbers of hormone-positive breast cancers is the use of oral birth control.  The CDC found that roughly 14% of U.S. women between the ages of 15 and 49 take oral birth control. Oral birth control artificially raises the levels of estrogen and progesterone circulating within the body, which could contribute to a growth of hormone-positive cancer. 


Breast cancer is an extremely treatable form of cancer. When detected early, the chances of remission increase and complications from the cancer decrease. With the rise in younger women developing breast cancers, it is more important than ever to educate women on the risk factors and the tools they can utilize to decrease their overall risk. Beginning mammograms as soon as possible, advocating for their care, and routine monitoring is essential for every female to ensure early detection.