In a study reported in JAMA Oncology by Chelain R. Goodman, MD, PhD, of the Department of Radiation Oncology at Northwestern University Feinberg School of Medicine, and colleagues, adjuvant radiotherapy was associated with better outcome in patients with early breast cancer who had detectable circulating tumor cells (CTCs).
The analysis included data from patients with stage pT1 to pT2 and pN0 to pN1 breast cancer and known CTC status from the National Cancer Database (NCDB) from January 2004 to December 2014 and the phase III SUCCESS trial from September 2005 to September 2013. A total of 1,697 patients from the NCDB cohort (1,681 women = 99.1%), with a median age of 63 years, and 1,516 from the SUCCESS cohort, with a median age of 52 years, were included in the analysis. CTCs were detected in 399 patients (23.5%) in the NCDB cohort and 294 (19.4%), in the SUCCESS cohort. Adjuvant radiotherapy was received by 57% of CTC-negative and 57% of CTC-positive patients in the NCDB cohort and by 82% of CTC-negative and 84% of CTC-positive patients in the SUCCESS cohort.
The association of radiotherapy with survival was dependent on CTC status in the NCDB cohort, with 4-year overall survival rates of 94.9% among CTC-positive patients who received radiotherapy, 88.0% among CTC-positive patients who did not receive radiotherapy, 93.9% among CTC-negative patients who received radiotherapy, and 93.4% among CTC-negative patients who did not receive radiotherapy (overall P < .001). A significant interaction of CTC status and radiotherapy with 5-year disease-free survival was observed in the SUCCESS cohort, with rates of 88.0% for CTC-positive/radiotherapy, 75.2% for CTC-positive/nonradiotherapy, 92.3% for CTC-negative/radiotherapy, and 88.3% for CTC-negative/nonradiotherapy (overall P = .04).
In the NCDB cohort, radiotherapy was associated with longer overall survival in patients with CTCs (time ratio [TR] = 2.04, P < .001) but not in patients without CTCs (TR = 0.80, P = .33). In the SUCCESS cohort, CTC-positive patients who received radiotherapy had longer local recurrence-free survival (TR = 2.73, P < .001), disease-free survival (TR = 3.03, P < .001), and overall survival (TR = 1.83, P = .003).
In patients from both cohorts who had breast-conserving surgery, radiotherapy was associated with longer overall survival in those with CTCs (TR = 4.37, P < .001) but not in those without CTCs (TR = 0.87, P = .77). Radiotherapy was not significantly associated with overall survival after mastectomy in CTC-positive or CTC-negative patients.
The investigators concluded, “Treatment with [radiotherapy] was associated with longer [local recurrence-free survival, disease-free survival, and overall survival] in patients with early-stage breast cancer and detectable CTCs.... A prospective trial evaluating CTC-based management for [radiotherapy] after breast-conserving surgery in women with early-stage breast cancer is warranted.” ■