Detecting circulating plasma tumor DNA in patients with early-stage cancer has the potential to influence selection of adjuvant systemic therapy. In a study reported in Clinical Cancer Research, Beaver and colleagues found that plasma tumor DNA could be detected both before and after surgery in patients with early-stage breast cancer.
Sanger sequencing of 30 tumors from 29 patients for PIK3CA mutations tumors identified 7 exon 20 and 3 exon 9 mutations. Analysis of tumors by droplet digital polymerase chain reaction, a new sensitive and specific method for mutation detection, confirmed these mutations and identified 5 additional mutations.
Droplet digital polymerase chain reaction analysis of presurgery plasma samples from the 29 patients identified 14 of the 15 PIK3CA mutations detected in the tumors, with no mutations being found in plasma from patients with PIK3CA wild-type tumors (sensitivity = 93.3%, specificity = 100%). Analysis of postsurgery plasma from 10 patients with presurgery mutation-positive plasma tumor DNA showed that 5 still had detectable plasma tumor DNA.
The investigators concluded, “This prospective study demonstrates accurate mutation detection in tumor tissues using [droplet digital polymerase chain reaction], and that [plasma tumor DNA] can be detected in blood before and after surgery in patients with early-stage breast cancer. Future studies can now address whether [plasma tumor DNA] detected after surgery identifies patients at risk for recurrence, which could guide chemotherapy decisions for individual patients.” ■
Beaver JA, et al: Clin Cancer Res 20:2643-2650, 2014.