Mammography is more sensitive than clinical examination for the early detection of subsequent breast tumors in women who have already had the disease, according to an interntational study published online today in the Annals of Oncology. If subsequent cancers are detected at the asymptomatic stage, the chances of survival are increased.
The authors wrote that if the second breast cancer was picked up at its early, asymptomatic stage, then the women's chances of survival were improved by between 27 and 47 percent compared with women whose second breast cancer was detected at a later stage when symptoms had started to appear.
According to the investigators, attempts to investigate the impact of early detection has been complicated by the fact that it is not possible to run randomized controlled trials because women who have already had one breast cancer are at higher risk of a relapse or a second breast cancer and, therefore, are generally advised to have regular breast checks as part of their follow-up care. What studies there have been have not made adjustments for the main factors that could bias the findings from a non-randomized study and often have looked at breast cancers occurring in either the same breast (ipsilateral relapse) or the other breast (contralateral) but not either breast.
The current study looked at 1,044 women who had attended one clinical center in Florence, Italy, between 1980-2005 and who had developed a second breast cancer. In that time 455 women had ipsilateral breast cancers (IBC) diagnosed and 589 women had contralateral breast cancers (CBC) diagnosed. Of these second cancers, 67 percent were asymptomatic and 33 percent were symptomatic.
The researchers found that mammography was more sensitive than a clinical exam for detecting second cancers (86 vs. 57 percent). However, 13.8 percent of cases were detected by clinical exam only. Asymptomatic cancers were smaller than symptomatic for both IBC and CBC; early stage cancers were more frequent in asymptomatic (58.1 percent) than in symptomatic (22.6 percent) women; and fewer women with asymptomatic than symptomatic CBC had node metastases.
In the analysis, the researchers from Italy, Australia and the United Kingdom adjusted to allow for lead-time bias (bias caused by an earlier detection of the cancer) and length-time bias (bias caused by the fact that some breast cancers develop more slowly than others and, therefore, are more likely to be detected at the asymptomatic stage and are less likely to cause death).
"Intuitively, it makes sense to consider that early detection of second breast cancers will improve prognosis, since breast cancer survivors have a long-term risk of developing further disease or relapse in either breast. However, due to a paucity of evidence about this until now, current recommendations on surveillance of breast cancer survivors vary substantially between countries and organizations," said the study's lead author Nehmat Houssami, MD, a breast physician and principal research fellow at the University of Sydney's School of Public Health in Australia.
"Our study provides new evidence on several aspects of early detection of second breast cancers," she said. "We set out to estimate the effect of early, asymptomatic detection while adjusting for the two main biases known to be associated with non-randomized studies of the impact of early detection - lead time and length bias - so we believe that the estimates we report are more valid than previously reported estimates, while acknowledging the limitation that the evidence is not from a randomized controlled trial."
"In addition, we have estimated this for early detection of either ipsilateral or contralateral breast cancer, while other studies have focused on one or the other. So our estimates may be more useful for clinicians discussing this aspect of breast cancer follow-up with their patients," Houssami noted.
"To our knowledge, this is the only study to have taken length-time bias into account when quantifying the impact of early, asymptomatic detection of breast cancer. This is important because slow-growing or indolent cancers have a much smaller probability of proving fatal, and this group of women will tend to be over-represented in the early-detected cancers, biasing the effect of screening to make it appear more beneficial," she concluded.
The researchers wrote that "recommendations on follow-up after treatment of early breast cancer should consider our findings,