No One-Size-Fits-All Answer for Breast Cancer Screening
October 17, 2007
Recent research showing the value of an MRI scan for women at high risk of developing breast cancer is also fueling confusion about when an MRI is appropriate. At the recently concluded Breast Cancer Symposium at Norris Cotton Cancer Center, radiologist Dr. Petra Lewis examined the pros and cons of breast cancer screening with MRI, and offered the conclusion that no single imaging technique offers the only solution for detecting breast cancer.
"MRI is a great tool for high risk patients," says Lewis."In women who are at markedly higher risk of developing breast cancer, such as those with certain genetic mutations, MRI picks up about twice as many cancers. We also use it for some women who have a moderately increased lifetime risk of breast cancer and who have dense breasts. It is also used for patients where there is a concern about the recurrence of a tumor at a lumpectomy site, and in patients with a new diagnosis of breast cancer to screen both breasts for additional disease."
Lewis says there's no doubt that when an MRI is used with high-risk patients, its ability to locate small or hard-to-find cancers outweighs its risks. However, Lewis says that mammography and ultrasound are not obsolete technologies by any means, and that in some cases, an MRI scan may miss cancers that mammography would detect. MRI scans can also sometimes be too sensitive, leading to a much higher rate of false positives (detecting something as cancerous that is non-cancerous). Lewis, estimates that the call-back rate for follow-up visits after a breast MRI is 20 percent, while for a screening mammogram it's closer to 10 percent.
There are other limitations to an MRI scan replacing a mammogram as a general screening tool. The availability of MRI machines is limited because not all institutions have them and they are in high demand for a variety of other medical procedures. Another concern is expense - the cost of an MRI is ten times that of a mammogram. While most major insurance companies will pay for an MRI if a woman is at high risk, they may not if she is at lower risk.
Lewis says that one important step is first identifying patients at higher risk by using a computerized risk assessment tool, such as the one known as the "Gail Model." It asks a simple series of questions about personal and family history to estimate a woman's chance of breast cancer. It then calculates a 5-year and lifetime risk of developing invasive breast cancer.
"If a woman has a Gail Model of greater than 25 percent and she has dense breasts, we may use MRI screening," explains Lewis.
While MRI may be considered the current gold standard for breast cancer detection, no one imaging technique is the sole solution for finding and preventing cancer. Radiologists like Lewis use the evidence gleaned from each technology, at different points in the diagnosis, to build a detailed understanding of each woman's condition.
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