Event-free survival (EFS) appears in 221 of 2,529 oncology trials, or 8.7%. It is most often a secondary endpoint, but when used as a primary endpoint it is associated with larger target sample sizes and late-stage confirmatory settings. The EFS signal is concentrated in haematologic malignancies, paediatric/orphan oncology, and multi-modality drug programs.
EFS is rare in pure Phase I oncology trials at 4 of 300 trials (1.3%), but becomes common once trials move into efficacy-driven development: 95 of 862 Phase II trials (11.0%) and 83 of 787 Phase III trials (10.5%) include EFS.
EFS behaves like an efficacy-maturity endpoint: it is uncommon in early dose-finding trials but reaches about one in ten trials in Phase II and Phase III settings where durable disease control, relapse prevention, or treatment failure can support clinical decision-making.
The EFS share falls from 158 of 1,689 trials in 2024 (9.4%) to 47 of 603 in 2025 (7.8%) and 16 of 237 in 2026 (6.8%).
The downward pattern suggests the 2026 oncology cohort is more weighted toward trials where EFS is not the dominant efficacy frame, while 2024 carried a broader mix of late-stage and haematology-heavy studies using EFS.
Among 221 EFS trials, 142 use EFS as a secondary-only endpoint (64.3%), 51 use it as primary-only (23.1%), and 28 include EFS in both primary and secondary endpoint sets (12.7%).
EFS is more often used to complement survival, response, and safety endpoints than to carry the full primary efficacy claim. Still, 79 of 221 EFS trials (35.7%) place EFS in the primary endpoint set.
Haematologic malignancies account for 133 of 221 EFS trials (60.2%) and have an EFS rate of 12.4% across the oncology dataset. Breast and genitourinary cancers follow at 22 EFS trials each.
| Disease label | EFS trials | Rate |
|---|---|---|
| Acute myeloid leukemia | 32 / 79 | 40.5% |
| Other oncology | 31 / 633 | 4.9% |
| Acute lymphoblastic leukemia | 28 / 53 | 52.8% |
| Breast cancer | 22 / 294 | 7.5% |
| DLBCL / large B-cell lymphoma | 17 / 63 | 27.0% |
| Bladder / urothelial cancer | 16 / 101 | 15.8% |
| Non-small cell lung cancer | 14 / 338 | 4.1% |
| Follicular lymphoma | 10 / 36 | 27.8% |
| Hodgkin lymphoma | 10 / 62 | 16.1% |
| CLL / SLL | 8 / 59 | 13.6% |
EFS is especially aligned with blood cancers where relapse, response failure, molecular persistence, and treatment failure are clinically meaningful events before overall survival matures.
EFS appears in 54 of 191 paediatric oncology trials (28.3%) versus 167 of 2,338 non-paediatric trials (7.1%). It also appears in 61 of 290 orphan-drug oncology trials (21.0%) versus 160 of 2,239 non-orphan trials (7.1%).
The enrichment is consistent with settings where relapse-free or failure-free disease control can be more feasible and clinically interpretable than waiting for mature overall survival.
EFS trials most often include small molecules (176 of 221, 79.6%) and monoclonal antibodies (112 of 221, 50.7%). Bispecific antibody and ADC programs show the highest EFS penetration among major modalities: 14.6% and 13.9%, respectively.
EFS is not tied to one therapeutic technology. Its higher rate in bispecifics, ADCs, and cell therapy reflects use in immuno-oncology and haematology settings where event definitions can capture durable control before survival readout.
Across 221 EFS trials, death appears in 118 EFS definitions (53.4%), relapse or recurrence in 100 (45.2%), and progression in 85 (38.5%).
The dataset shows EFS as a composite endpoint rather than a single standardized event construct. Death, relapse, and progression dominate, but surgery-related failure, treatment failure, toxicity, MRD, and secondary malignancy appear in narrower clinical contexts.
A fixed EFS time window appears in 50 of 221 trials (22.6%). The most common windows are two-year EFS (20 trials, 9.0%), three-year EFS (15 trials, 6.8%), and one-year or 12-month EFS (14 trials, 6.3%).
Most EFS endpoints are framed as time-to-event endpoints without a named landmark year. Landmark EFS is present, but it is a minority pattern and appears mainly where relapse prevention or early treatment failure is operationalized at defined follow-up points.
Imaging-related wording appears in 91 of 221 EFS trials (41.2%). Explicit investigator assessment appears in 27 (12.2%), independent review in 15 (6.8%), and RECIST in 12 (5.4%).
Unlike progression-free survival, EFS wording often depends on protocol-defined clinical events rather than a single cross-tumor measurement standard. Imaging is common, but named criteria such as RECIST, Lugano, ELN, or STEEP appear in smaller subsets.
Among EFS trials, overall survival (OS) appears in 201 of 221 (91.0%), safety or adverse-event endpoints in 186 (84.2%), and response endpoints in 173 (78.3%).
EFS rarely stands alone. It is usually embedded in a broader endpoint architecture that preserves OS as the survival anchor while adding response, safety, molecular, and biomarker evidence around the EFS result.
EFS trials average 11.3 total endpoints with a median of 10, compared with 7.0 total endpoints and a median of 6 in non-EFS oncology trials.
EFS is associated with broader endpoint packages. The difference is driven mainly by secondary endpoints, consistent with EFS trials needing supporting survival, response, safety, biomarker, and patient-centered measures.
Among EFS trials, 128 of 221 are randomized (57.9%), compared with 1,126 of 2,529 in the overall oncology set (44.5%). Median target sample size is 136 in EFS trials versus 105 in non-EFS trials; when EFS is in the primary endpoint set, the median rises to 278.
EFS is operationally heavier when it becomes decision-bearing. Primary-EFS trials have a median target sample size more than three times higher than secondary-only EFS trials, indicating a shift from supportive efficacy characterization to confirmatory endpoint strategy.
EFS means event-free survival. OS means overall survival. PFS means progression-free survival. MRD means minimal or measurable residual disease. ADC means antibody-drug conjugate. RECIST, Lugano, ELN, and STEEP are endpoint or response-assessment frameworks used in selected oncology settings.