All women with average risk of breast cancer should begin getting an annual screening mammogram at age 40. But increasing age isn't the only factor that raises a woman's risk of breast cancer.

"If other factors known to increase a woman's risk of breast cancer are present, we start thinking about screening earlier," says Dr. Kai Sun, a breast cancer doctor at Houston Methodist. "The goal is always to detect abnormalities as early as possible, when breast cancer is most curable."

If a woman's breast cancer risk is determined to be high, mammography and/or other types of imaging will need to begin earlier than age 40.

But how do you know if your risk is higher than average? And if you are high risk, how early should screening begin?

Who is considered high risk for breast cancer?

High-risk breast cancer factors include having a:

• Personal history of breast cancer
• Certain genetic mutation(s) linked to breast cancer risk, like BRCA1 and BRCA2
• History of radiation therapy to the chest (usually the result of lymphoma treatment between the ages of 10 to 30)
• Strong family history of breast cancer
  
  

For the latter point, it's important to note that having a family member who has breast cancer, or had it in the past, doesn't automatically mean you are at higher risk.

"We have models that incorporate a variety of details about a person's family history and provide a score of their risk," explains Dr. Sun. "The models take several factors into account, including whether it's a first-degree relative, age of breast cancer onset, if a history of ovarian cancer is also present and more."

For instance, if your mother had breast cancer early — before her 50s — your risk is higher than if she was diagnosed in her 60s or 70s. And this is just one of the factors these models consider.

"If the models assess the lifetime chance of having breast cancer to be 20% or higher, that's considered high risk," says Dr. Sun. "If they find the 5-year risk to be higher than 1.7%, that's also high risk.

Where should you start if you're worried about your breast cancer risk?

Dr. Sun notes that, ideally, women are regularly seeing their doctors and updating them on changes in their personal or family health history as they arise. (Related: 5 Reasons You Need a Primary Care Doctor in Your 20s & 30s)

"Most of the people I assess for high-risk breast cancer get referred to me because their primary-care doctor or gynecologist has flagged something during a routine wellness check," says Dr. Sun. "But if a person is concerned about their breast cancer risk, they should certainly be proactive and bring it up themselves, too."

A referral to a high-risk clinic is often the next step.

"At this point, we formally assess a person's lifetime and 5-year risk," says Dr. Sun. "Sometimes this includes referral to a genetic counselor, who can decide if genetic testing might be beneficial."

If risk of breast cancer is determined to be high, your doctor will help you understand which type of breast imaging is right for you moving forward.

What does early breast cancer screening entail?

While an annual screening mammogram is the gold standard for women with an average risk of breast cancer, those at higher risk almost always need a different type (or types) of imaging, including diagnostic mammograms, MRIs and/or ultrasounds. They'll also likely need imaging more frequently, typically every six months.

(Related: Screening Versus Diagnostic Mammograms: What You Can Expect)

"When someone is high risk, we usually want more detailed, frequent imaging from the start," says Dr. Sun. "For someone whose lifetime breast cancer risk is higher than 20%, for instance, I might order alternating diagnostic mammograms and MRIs so that patients have some kind of imaging done every six months."

The exact type of imaging needed depends on age, breast tissue density and specific breast cancer risk factors, according to Dr. Sun. Your doctor will help you understand what you need and why.

When should high-risk breast cancer screening begin?

When exactly mammograms and the other types of imaging should begin if you are at higher risk also depends on your specific breast cancer risk factors.

"For a woman with a BRCA1 mutation, for instance, we start some type of imaging at age 25, or 10 years before the earliest breast cancer case in the family, whichever comes first," explains Dr. Sun.

Needing to start screening at such a young age might surprise you, but it's why Dr. Sun emphasizes the importance of having a doctor and making time for routine check-ups. If necessary, your doctor will refer you to a specialist — like Dr. Sun if there's a concern about your breast cancer risk — for a more formal evaluation of your health risks.

And on a separate but related note, your primary-care doctor is also your first point of contact if you notice a breast lump, which could also be a reason that a mammogram — diagnostic mammogram, to be exact — may also be needed earlier than age 40.

"Every woman should have a primary-care doctor and gynecologist," says Dr. Sun. "Risk of breast cancer, as well as other health conditions, isn't something a person should try to gauge on their own. And early screening is essential."