Phase II Trials in Radiation Oncology: When Success Fails to Translate

Area of Science:

• Radiation oncology clinical trial design and progression.

Background:

• Phase II trials are crucial for selecting treatments for Phase III studies.
• The effectiveness of Phase II radiation oncology trials in guiding Phase III progression is not well understood.

Purpose of the Study:

• To evaluate if Phase II cooperative group studies in radiation therapy effectively lead to Phase III testing.
• To identify factors influencing the progression of Phase II trials to Phase III.

Main Methods:

• Analysis of completed Phase II radiation therapy trials from the National Clinical Trials Network (2003-2019).
• Assessment of trial endpoint achievement and subsequent Phase III progression.
• Logistic regression to identify factors associated with Phase III transition.

Main Results:

• Only 17% of completed Phase II trials progressed to Phase III, despite 54% meeting their primary endpoint.
• 71% of successful Phase II trials did not advance, termed 'discordant successes'.
• Larger enrollment and longer trial duration were associated with Phase III transition, while toxicity endpoints were least likely to translate.

Conclusions:

• Most Phase II radiation oncology trials that meet endpoints do not advance to Phase III.
• Progression is hindered by structural and decisional barriers rather than statistical futility.
• Improved prespecification of advancement intent and use of decision-relevant endpoints could enhance trial impact.