SAN FRANCISCO—Acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) are known complications associated with adjuvant chemotherapy in breast cancer patients, but the actual rate has been a matter of discussion within the oncology community recently. A new retrospective analysis, though, reported here at the Breast Cancer Symposium (Abstract 62) suggests the complication rate in a large community oncology practice is similar to what has been reported in clinical trials and is lower than that seen in recent database studies.
The researchers, led by Neelima Denduluri, MD, a medical oncologist and hematologist with Virginia Cancer Specialists and the U.S. Oncology Network, analyzed the electronic health records of 20,900 female breast cancer patients who had been treated in the U.S. Oncology system between 2007 and 2010. Patients in the study had stage I to III disease and were followed through February 2012.
With a median follow-up of 2.8 years, 11,295 women (54%) had received chemotherapy and 9,605 (46%) had not. The most striking difference between the two groups, she noted, was that the median age at diagnosis for the no-chemotherapy group was 10 years older than for the chemotherapy-treated group (64 vs. 54 years).
“Our overall event rate was very low and not statistically significant,” she said. Twelve women (0.167%) in the chemotherapy group developed AML or MDS, compared with 16 (0.106%) in the no-chemotherapy group.
In the chemotherapy-treated group, older age and anthracycline treatment were significantly associated with the risk of AML/MDS in a multivariate analysis. Pegfilgrastim use was not significantly associated with AML/MDS.
In the no-chemotherapy group, none of the variables tested were significantly associated with risk, although age and disease stage showed a trend toward significance.
During the discussion following the presentation, Clifford Hudis, MD, Chief of the Breast Cancer Medicine Service at Memorial Sloan-Kettering Cancer Center, thanked her for a clear presentation and the creative use of electronic medical records for comparative effectiveness research.
He then alluded to recent database studies that showed substantially higher rates of AML/MDS in breast cancer patients, particularly in women who had received growth factors during adjuvant treatment. “Your data are much more in line with clinical trial data,” he said. “Do you have any thoughts on that disconnect between large population-based studies like yours and huge SEER database studies?”
“I think many of the SEER database studies are using Medicare claims,” Denduluri responded. “Our population included both younger and older patients.” Clinical trials, she noted, tend to enroll younger patients, which might help explain why the rate is lower than that seen in database studies and more similar to what has been seen in large clinical trials, such as those that tested dose-dense chemotherapy.
One limitation to the study is the relatively short follow-up, she continued. “But as a comment, the vast majority of topoisomerase-induced leukemias are detected within the first three years.
“The rates of AML/MDS were low after adjuvant chemotherapy and were similar to those of non-chemotherapy treated patients. Our data confirm known risk factors of AML/MDS after chemotherapy, including increased age and anthracycline use. In our analysis, the growth factor affect was not significant.”