A new blood test may help identify which people with early-stage breast cancer are at higher or lower risk of their cancer coming back after treatment. Researchers say this could be an important step toward more personalized care for patients with hormone receptor‑positive, HER2‑negative disease.
Study focus
Researchers reported early results from the international phase III PALLAS study, which enrolled people with stage II–III hormone receptor‑positive, HER2‑negative breast cancer. The analysis looked at whether tiny traces of cancer DNA left in the blood after surgery and standard treatments could predict the risk of cancer returning in distant parts of the body.
What is MRD and the Signatera test?
The study used a personalized blood test called Signatera, which looks for molecular residual disease (MRD)—very small amounts of cancer DNA (ctDNA) that may remain in the body after treatment. In this trial, blood was drawn for MRD testing after surgery (and chemotherapy and/or radiation when given), at the start of adjuvant therapy, again around six months, and at the end of two years of study treatment.
Key findings for patients
- Most patients (about 9 out of 10) were MRD‑negative after surgery and had excellent outcomes, with very low rates of distant recurrence over five years.
- A small group (about 1 out of 10) were MRD‑positive and had a much higher risk of the cancer spreading later, even though they received standard endocrine therapy and the study treatment.
These patterns were consistent at all the time points tested, showing that MRD status was a strong signal of distant recurrence risk, over and above usual clinical and pathology features.
What this could mean for care
The PALLAS treatment comparison itself did not show a benefit from adding the CDK4/6 inhibitor palbociclib to endocrine therapy in early breast cancer, and palbociclib is not approved for this setting. However, the new MRD results suggest that ongoing ctDNA monitoring after surgery could help:
- Reassure MRD‑negative patients who appear to have a very low risk of distant recurrence.
- Identify MRD‑positive patients who may need closer follow‑up or consideration for more intensive or novel treatments in future trials.
Experts say these findings move the field closer to MRD‑informed, personalized management of early‑stage HR‑positive, HER2‑negative breast cancer, rather than a one‑size‑fits‑all approach.
Reference
Parsons HA, et al. Tumor-informed circulating tumor DNA analysis to assess molecular residual disease for prognosis and prediction of benefit from palbociclib in the PALLAS trial. Presented at: San Antonio Breast Cancer Symposium (SABCS); 2025 December 9-12; San Antonio, Texas, United States. #RFS-04.
