When Should Cancer Patients Switch Treatment? Researchers Build a Standard Rulebook for a Key Clinical Milestone

In modern cancer medicine, few moments carry as much weight as the day a patient and their doctor decide that the current therapy is no longer working and it is time to move on to the next one. That moment, known in clinical research as time to subsequent therapy, or TTST, has quietly become one of the most widely used intermediate endpoints in oncology trials and in regulatory benefit assessments. Yet until now, there has been no agreed, standardized way to document what actually happens when a patient switches treatment, or why. A new study published in the Journal of Cancer Research and Clinical Oncology set out to close that gap, and its findings could reshape how cancer clinical trials capture one of the most meaningful events in a patient’s treatment journey.

The research team, led by Bianca Biedenweg, Thomas Kohlmann, and Janine Ziemann of University Medicine Greifswald in Germany, together with colleagues from patient advocacy organizations, clinical centers, and the pharmaceutical industry, pursued a deceptively simple question: can time to subsequent therapy be considered an endpoint that genuinely matters to patients, and if so, how should the events that define it be recorded in a consistent, comparable way across studies? To answer it, they combined a systematic literature review, an analysis of case report forms from international randomized controlled trials, a review of documents from the German Federal Joint Committee, the body that decides which drugs are reimbursed under Germany’s AMNOG system, and, crucially, the direct voices of patients, relatives, and healthcare professionals.

The study focused on five major oncological indications: breast cancer, prostate cancer, melanoma, multiple myeloma, and non-small cell lung cancer. These diseases were chosen because they represent some of the most active areas of drug development, where patients typically move through several lines of therapy over the course of their illness. In each of these settings, the moment of switching to a subsequent treatment marks a turning point that clinicians recognize instantly, but that has historically been recorded in clinical databases with little structure. The researchers wanted to know whether that turning point could be captured with enough precision and enough patient-centered context to serve as a reliable, meaningful endpoint in its own right.

The qualitative phase of the study involved semi-structured interviews with 35 individuals, including patients, relatives, and healthcare professionals. The results were striking in their consistency: the overwhelming majority rated time to subsequent therapy as particularly significant. For patients, the moment of switching treatment is not an abstract statistical event. It often signals that the current therapy has stopped controlling the disease, that symptoms may be progressing, or that a new phase of the cancer journey has begun. For clinicians, it marks a concrete, observable clinical decision. The alignment between these two perspectives is precisely what makes TTST a candidate for a patient-relevant intermediate endpoint, a category of outcomes that regulators increasingly demand when overall survival data are not yet mature.

To test and refine these qualitative findings, the team conducted a two-stage Delphi survey, a structured consensus method in which experts answer questionnaires in successive rounds and the results are fed back to them until agreement emerges. The first round attracted 264 respondents, and 117 completed the second round. The participants, drawn from the ranks of healthcare professionals, patients, and relatives, were asked to evaluate whether TTST should be regarded as patient-relevant. In the end, 81 percent of respondents confirmed its patient relevance, with a 95 percent confidence interval ranging from 76 to 85 percent. That level of agreement across such a diverse group of stakeholders is rare in endpoint research and provides a strong empirical foundation for the study’s central claim.

But confirming that a switch of therapy matters to patients was only half the challenge. The researchers also needed to define precisely which circumstances justify counting a switch as an event. Through their combined analysis, they identified nine distinct treatment scenarios that can legitimately trigger the start of subsequent therapy. These scenarios distinguish, for example, between a planned treatment sequence, a change driven by disease progression, and a change driven by intolerance or side effects. Without such differentiation, an endpoint like TTST can be ambiguous: two trials might report similar times to subsequent therapy while the underlying clinical situations were fundamentally different. The nine-scenario framework gives trial designers and regulators a shared vocabulary for interpreting what a TTST result actually means.

The practical output of the study is a pair of documentation checklists designed to be used prospectively in clinical trials and, potentially, in routine clinical care. The first is a comprehensive master checklist intended for flexible, complete documentation of the reasons for and consequences of a therapy change. The second is a shortened version focused specifically on therapy-change items, suitable for settings where brevity is essential. Both instruments combine standardized response formats with free-text fields, allowing researchers to capture structured, comparable data while still preserving the individual nuances of each patient’s situation. The checklists were developed to ensure that the characteristics demonstrating patient relevance are collected systematically rather than left to the judgment of individual investigators.

The implications for clinical research are considerable. In oncology trials, overall survival remains the gold standard endpoint, but as therapies improve and patients live longer, survival differences become harder and slower to demonstrate. Intermediate endpoints such as progression-free survival have filled the gap, but they depend on radiological assessments that may not always reflect how a patient actually feels or functions. Time to subsequent therapy offers an appealing alternative because it is anchored in a concrete clinical decision that is easy to verify and, as this study now demonstrates, is regarded as meaningful by patients themselves. With standardized documentation, TTST could be compared more reliably across trials, incorporated more confidently into health technology assessments, and used more transparently in regulatory benefit evaluations such as those conducted under Germany’s AMNOG framework.

The study also carries a broader message about how endpoints should be developed. Rather than relying solely on the technical judgment of clinicians and statisticians, the Greifswald team deliberately built patients and relatives into every stage of the process, from the initial interviews through the Delphi consensus rounds. The ethics committee of University Medicine Greifswald reviewed the study, and all participants provided written informed consent. The work was supported by an unrestricted institutional grant to University Medicine Greifswald and by the German Association of Research-Based Pharmaceutical Companies, with the authors disclosing employment relationships with industry alongside the absence of conflicts among several clinical and patient-representation co-authors. The findings were presented in part at the European Society for Medical Oncology 2025 Annual Congress in Berlin and at the German Cancer Conference 2026, signaling that the oncology community is already paying close attention.

For patients, the practical promise of this research is that the story of their treatment journey may soon be told more completely and more faithfully in the trials that shape tomorrow’s standards of care. When a clinical trial reports not just how long patients stayed on a drug, but why they switched, what triggered the change, and what happened as a result, the resulting evidence becomes richer and more human. Time to subsequent therapy, once a loosely defined afterthought in trial databases, now has the beginnings of a rigorous, patient-validated framework. As new cancer therapies continue to extend and reshape the course of disease, endpoints like TTST, documented with the standardization this study provides, will help ensure that clinical research measures not only what happens inside tumors, but what matters most to the people living with them.

Subject of Research: Development and patient-relevance validation of time to subsequent therapy as a standardized clinical trial endpoint in oncology

Article Title: Time to subsequent therapy (TTST) as an endpoint in clinical studies: development of standardized documentation of subsequent therapy through systematic literature review, expert interviews, and Delphi survey

Article References: Biedenweg, B., Ruppert, T., Kohlmann, T., Danner, M., Mehnert-Theuerkauf, A., Lüftner, D., Filippig, U., Ziemann, J., Osowski, U., & Kaskel, P. (2026). Time to subsequent therapy (TTST) as an endpoint in clinical studies: development of standardized documentation of subsequent therapy through systematic literature review, expert interviews, and Delphi survey. Journal of Cancer Research and Clinical Oncology, 152(9), Article 179. https://doi.org/10.1007/s00432-026-06583-w

Image Credits: AI Generated

DOI: 10.1007/s00432-026-06583-w

Keywords: time to subsequent therapy, TTST, clinical trial endpoints, oncology, patient relevance, Delphi survey, breast cancer, prostate cancer, melanoma, multiple myeloma, non-small cell lung cancer, benefit assessment