Effectiveness Without Efficacy: Cautionary Tale from a Landmark Breast Cancer Randomized Controlled Trial

Area of Science:

• Oncology
• Clinical Trials
• Biostatistics

Background:

• Previous trials established equivalence between breast conserving therapy (BCT) and total mastectomy (TM) for early breast cancer.
• Recent studies suggest improved survival with BCT, necessitating reconciliation of findings.
• This study re-analyzed B-06 trial data and performed simulations to clarify survival outcomes.

Purpose of the Study:

• To reconcile conflicting literature on breast cancer treatment outcomes.
• To evaluate the impact of late other-cause deaths on treatment comparisons.
• To assess the power of clinical trials to detect survival differences between BCT and TM.

Main Methods:

• Estimated survival distributions (overall survival, breast-cancer-specific death, other-cause-specific death) for BCT and TM arms.
• Utilized restricted mean survival time (RMST) and hazard ratios for comparisons.
• Simulated cause-specific death times to assess power under various scenarios, including modified radiation effects.

Main Results:

• With 200 months follow-up, BCT showed an average gain of 3.7 months in OS and 4.5 months in BCSD over TM.
• Simulations indicated that a trial size of 5,000 per arm could achieve 79.2% power for OS and 92.4% for BCSD.
• An excess of other-cause-specific death (OCSD) in the BCT arm was observed after 144 months, particularly after 200 months.

Conclusions:

• Late excess OCSD in the BCT arm, potentially radiation-related, and limited sample sizes hindered the detection of BCT superiority.
• When simulated OCSD reflected no radiation, estimated OS gain increased, and statistical power improved.
• Considering the radiation practices of the B-06 trial era, BCT and TM demonstrate comparable survival outcomes.