Evidence that surveillance by mammogram in breast cancer survivors has been lacking until now
It is estimated that 14% of all cancer survivors within the database were diagnosed with a second cancer during 25 years of follow-up (Fraumeni, et al.). Thus, a hallmark of survivorship care is the vigilance on prevention and early detection of second cancers. For female cancer survivors, this includes ensuring that mammograms are done annually, as is recommended by multiple organizations including the American Cancer Society and the American Society of Clinical Oncology. However the evidence that surveillance by mammogram in breast cancer survivors has been lacking until now.
Using data from the Breast Cancer Surveillance consortium Houssami and colleagues identified 19,078 women with a personal history of breast cancer and matched them for breast density, age group, year of mammogram, and registry site, to 55,315 women who did not report a personal history of breast cancer. In total 58,870 mammograms in each cohort were included in this analysis, indicating that breast cancer survivors were utilizing more surveillance than those without breast cancer. The study aimed to define accuracy of mammography, cancer detection rate, the prevalence of interval cancers, and stage at diagnosis among screening detected malignancies.
Their study showed that while screening mammography successfully picked up interval malignancies in both cohorts (6.8 cases per 1000 screens among breast cancer survivors vs. 3.6 per 1000 screens in women without a history of breast cancer), those with a history of breast cancer had more than double rate of interval cancer detection (3.6/1000 screens) compared to those without a history of breast cancer (1.4/1000 screens). Thus, compared to those being screened without a history of breast cancer, the sensitivity of mammograms among breast cancer survivors was only 65% though specificity was 98%. In simple terms it means that you had a 35% chance of the mammogram not picking up your cancer, but if it did detect the cancer, it was highly unlikely to be wrong. Embedded in the analysis, however, were several interesting findings which for breast cancer survivors should be encouraging: (1) the rate of abnormal mammogram results was very low (2.3% in this group vs. 1.4% in women without breast cancer); (2) screening sensitivity improved with time from 60% in the first 5 years to 70% in the subsequent years; (3) was similar in its ability to detect contralateral and ipsilateral breast cancer; and (4) the cancers picked up with screening were early stage for the most part.
So, what's the take home message? For me it is that mammography does work as a screening program for breast cancer survivors. The fact that there are more interval detected cancers in breast cancer survivors should make both patients and their providers more vigilant and not to assume that a normal mammogram means "all is well until the next one". Careful surveillance does not rest on one test alone; it rests on frequent visits to your physicians for routine examination and interval history. While not one strategy has been shown to be ideal, we must continue to use the tools available to us to care for cancer survivors. For BRCA-mutation carriers my center has an approach that alternates mammography with breast MRI with hope of improving early detection during the screening of cancer survivors. With time we may learn more about the benefits of more aggressive screening methodologies, but this important paper has given us important data on which to improve upon.
JF Fraumeni, et al. New malignancies among cancer survivors: SEER cancer registries, 1973-2000.
N Houssami, et al. JAMA. 2011;305(8):790-799. doi: 10.1001/jama.2011.188