It doesn't seem like a trick question, but it has become one: At what age should a woman have her first mammogram?

Worldwide, breast cancer is the most common form of cancer. In the US, it ranks second only to lung cancer as the cause of cancer death among women and is a leading cause of early death among women.

Two other changes are almost as striking as the recommendation to delay screening to age 45.

It is estimated that 230,000 women will be diagnosed with breast cancer in 2015. Though improvements in early detection and treatment have helped decrease the number of deaths from breast cancer, still over 40,000 women will die of it this year.

Now the American Cancer Society (ACS) has decided that women with average risk for breast cancer can wait until age 45 to begin getting regular screening mammograms instead of starting them at 40, as the Society's guidelines had previously recommended.

The shift is designed to reduce the harms early screening can bring: false positives, unnecessary biopsies and surgeries. But not all experts agree: The American College of Obstetricians and Gynecologists still counsels women to get their first mammogram at 40.

The ACS's shift from its 2003 guidelines is based on an accumulation of new evidence from observational and randomized controlled studies of screening programs and long-term follow-up.

The new 2015 ACS breast cancer screening recommendations for women at average risk are as follows:

  • Women should undergo regular screening mammography starting at age 45.
  • Women 45 to 54 years of age should be screened annually.
  • Women 55 years and older should transition to biennial screening or have the opportunity to continue screening annually.
  • Women should have the opportunity to begin annual screening between the ages of 40 and 44 years.
  • Women should continue screening mammography as long as their overall health is good and they have a life expectancy of 10 years or longer.
  • Clinical breast examination is not recommended for breast cancer screening among average-risk women at any age.
  • Two other changes are almost as striking as the recommendation to delay screening to age 45. The first is the removal of the recommendation for periodic clinical breast examination by a woman’s physician; the second is that breast self-exams are no longer even discussed.

    Researchers found little evidence that such breast exams contributed significantly to the detection of cancer in women at average risk of any age. In fact, the evidence suggested that when added to mammography screening, clinical breast exams increased the rate of false-positive results. Physicians are advised to use the time normally spent in breast examination to discuss family history with women, counsel them to be alert to changes in their breasts, and talk about the potential benefits, limitations, and harms of screening mammography.

    The previous guidelines did not recommend breast self-examinations, but advised physicians to address it with their patients. There has been no evidence that self-examination improves outcomes; that is why the issue is not addressed in the 2015 guidelines.

    The authors of an editorial accompanying the article offer what may be the best advice: “[T]here is no single right answer to the question, ‘Should I have a mammogram?’ Instead, women should be supported in estimating and understanding their risk of developing breast cancer and articulating their values and preferences so that clinicians can help them make informed decisions.”

    You are your body's best advocate. Talk to your doctor. If you have a family history of breast cancer or are simply nervous about the possibility, nothing prevents you from seeking a mammogram at 40. These changes are not meant to drive you crazy; they are designed to protect you from unnecessary and potentially dangerous procedures.

    The new guidelines are published in JAMA Internal Medicine.