Overdiagnoses in Breast Cancer Can Happen, but Not Often Enough to Cause Alarm
Annual mammograms are a woman’s best defense against breast cancer. Screenings can lead to early diagnosis, which is key to getting a leg up on the spread of the cancer.
However, not all breast cancer diagnoses are the same. A recent study in Annals of Internal Medicine suggests that 1 in 7 breast cancer cases detected during screening is overdiagnosed, meaning the tumor found may never pose a threat to the person’s health during her lifetime.
So how can doctors determine whether a cancer is supposedly overdiagnosed? It’s a challenge, according to Dr. Dana Ataya, a breast radiologist at Moffitt Cancer Center.
“Since there is no way to determine when someone will die, we cannot know whether a diagnosed cancer may progress to affect that individual in their lifetime,” Ataya said. “In addition, we are not yet able to predict which cancers will progress versus not progress. That’s why it’s important for all women to have access to early detection and treatment of breast cancer.”
It is also important to consider what type of patients are included or excluded in studies. This one, Ataya points out, does not include women ages 40 to 49, which is unfortunate and can lead to incorrect assumptions.
“Overdiagnosis is overestimated in this study,” she said. “Other published research suggests that fewer than 10% of cancers are overdiagnosed. Studying overdiagnosis is challenging because of multiple factors, including that overdiagnosis cannot be directly observed, so assumptions are made.”
Overdiagnosis is also directly related to age and competing causes of mortality, Ataya said, so studies like this that do not include women ages 40 to 49 are overestimating overdiagnosis. According to Ataya, younger women diagnosed with breast cancer have higher rates of more aggressive cancer and are less likely to die from other causes.
However, not all cancers will advance into invasive malignancies that spread across the body, eventually leading to death. Some noninvasive cancers may halt progression at an early stage or grow slowly enough that they never pose a direct threat to a patient’s life.
“Discussions related to overdiagnosis should be reframed to focus on ductal carcinoma in situ (DCIS), which is a noninvasive form of breast cancer,” Ataya said. “It is important to remember that there is no compelling evidence that invasive cancers are overdiagnosed. In fact, we need to find invasive cancers as early as possible.”
While rare, some patients may undergo tests and biopsies for breast cancers that are noninvasive and indolent. Those extended tests may be uncomfortable, but necessary to ensure the patient remains healthy.
“We know that over 40,000 people will die from breast cancer this year,” Ataya said. “We also know that women who do not undergo regular mammograms are more likely to be diagnosed with larger and more advanced cancers. Screening mammography saves lives. If we detect a breast cancer before it has spread to other parts of the body, a woman has a greater chance at survival.”
Ataya points out that more work needs to be done to help classify DCIS, since up to 25% of DCIS lesions will be upgraded to an invasive cancer at the time of surgery while other DCIS lesions may never progress to that stage.
“If we knew with certainty that a woman had a DCIS lesion with very low risk for progression or upgrade, that would open the door to more options for the patient, like imaging surveillance rather than surgery,” she said. “We are doing cutting-edge research in this space here at Moffitt.”
With a recently awarded National Cancer Institute research grant, Ataya is part of a team led by Dr. Bethany Niell and Dr. Robert Gillies investigating radiomic and pathomic signatures that could ultimately be used to create a model to stratify DCIS lesions into high risk and low risk.
“One goal of our work is to address concerns related to overdiagnosis and overtreatment of DCIS lesions,” Ataya said.
Finding invasive cancers as early as possible remains the key to reducing cancer death rates by preventing the spread of disease to other parts of the body.
Moffitt recommends women get yearly mammograms beginning at the age of 40. If a woman is at a higher risk of breast cancer, screening should start earlier.
“The take home message is that the benefits of screening far outweigh any harms,” Ataya said. “Women should continue to get a yearly mammogram.”
