Natera Unveils MRD Data From Phase III PALLAS Trial In HR+/HER2- Breast Cancer

(RTTNews) - Natera Inc. (NTRA) announced initial translational research results from the international randomized Phase III PALLAS study. The findings were presented at the San Antonio Breast Cancer Symposium (SABCS) and highlight the prognostic value of molecular residual disease (MRD) status, measured by the Signatera Genome test, in stage II-III HR+/HER2- breast cancer.

The first dataset, derived from a U.S. biomarker cohort of 420 patients, demonstrated that MRD status after surgery (and adjuvant chemotherapy with or without radiation) is a highly predictive biomarker for distant recurrence risk. These results support Natera's strategy to integrate MRD testing into routine post-surgical risk assessment, enabling a more personalized approach to managing early-stage HR+ breast cancer. Data from a parallel ex-U.S. cohort, along with subgroup analyses, will be presented at a later date.

In the PALLAS trial, patients with stage II-III HR+/HER2- breast cancer were randomized to receive two years of palbociclib, a CDK4/6 inhibitor, in combination with endocrine therapy. Signatera MRD assessments were conducted at three key postoperative timepoints: baseline (the first day of protocol-directed therapy), approximately six months on-treatment (C6D1), and at the end of the two-year treatment period (EOT).

At baseline, approximately 92% of patients were MRD-negative and showed excellent outcomes, with a five-year distant recurrence-free interval (DRFI) of 93%. By EOT, MRD-negative patients had a five-year DRFI of 95%, underscoring that MRD-negativity after surgery and adjuvant endocrine therapy is associated with exceptionally low recurrence risk.

Conversely, baseline MRD positivity was observed in about 8% of patients. These individuals had a five-year DRFI of just 28%, reflecting a significantly higher risk of distant recurrence compared with MRD-negative patients (hazard ratio ~15). At EOT, MRD-positive patients had a five-year DRFI of 32%, with hazard ratios exceeding 20 versus MRD-negative patients.

Across all timepoints—baseline, C6D1, and EOT—Signatera ctDNA status was consistently and strongly associated with recurrence risk, even after adjusting for clinical and pathological features. MRD-positive patients demonstrated hazard ratios ranging from 13.4 to 21.5 compared with MRD-negative patients, showing far greater risk separation than typically observed with clinicopathologic factors alone.

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