A team of researchers led by Anne Marie McCarthy, PhD, from the University of Pennsylvania found that overweight and obese women had a 40% higher risk of early-stage cancer in the second year after a negative mammogram. The group also found that obese women had a 90% increased risk of advanced cancer in the first year, and both overweight and obese women had a 40% or greater increased risk in the second year.
"These results have important implications for risk assessment, screening intervals, and use of supplemental screening," the authors wrote.
Mammography reduces breast cancer mortality, but about 15% of breast cancers are diagnosed after a negative mammogram and before the next recommended screening examination, according to a 2015 study published in the American Journal of Roentgenology. Outcomes for these interval cancers are poorer than those for screen-detected cancers.
Meanwhile, much of the emphasis on who should receive supplemental screening has focused on breast density, McCarthy told AuntMinnie.com.
"Our findings highlight that while breast density is an important factor associated with short-term risk of advanced breast cancer, BMI is also an important risk factor that may need to be considered, since women with higher BMI are at higher short-term risk of advanced breast cancer," she said.
The research team included 293,520 negative mammograms performed from 2006 to 2015 among 74,736 women and evaluated several risk factors, such as breast density, BMI, and family history, to name a few.
Of the 1,345 breast cancers identified in the patients, 357 were advanced and 988 were at an early stage.
BMI was associated with advanced cancers in both years, but with early-stage cancers only in the second year after a negative mammogram. Breast density, prior biopsy, and family history were also associated with both early-stage and advanced cancer diagnoses.
McCarthy explained that when women develop breast cancer within a short time of a negative mammogram, two things might be happening. One is the cancer was present but missed by the interpreting radiologist. Alternatively, the cancer may not have been present at the time of the negative mammogram, but it developed quickly afterward.
"When we look at all cancers diagnosed within a short time of a negative mammogram, the cancers are probably a mix of both etiologies," she told AuntMinnie.com. "When we focus on the advanced cancers, these tend to be fast-growing. We know that obesity can create an environment conducive to aggressive tumor growth, which would explain the association of BMI with advanced cancers across both time periods."
McCarthy also said while most literature in the U.S. has focused on interval cancers using a definition of diagnosis within one year of a negative mammogram, this definition does not take into account the prognosis of the tumor.
"A small early-stage cancer diagnosed within one year of a negative mammogram is of less concern than an advanced stage tumor diagnosed two years after a negative mammogram," she said. "Additionally, the focus on the one-year screening interval ignores current screening recommendations and the real-world situation where not every patient is being screened annually."
McCarthy and her team wrote that women with a higher BMI should consider annual mammography or supplemental screening with breast MRI for potentially better detection of small and aggressive tumors.
Among the study's limitations were that it did not assess racial differences in cancer diagnosis, did not include information on screening that occurred outside the University of Pennsylvania health system, and it did not consider whether patients received breast MRI or ultrasound screening following mammography.
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