What Are DFS (Disease-Free Survival) and EFS (Event-Free Survival)?
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In cancer treatment, another question is as important as “How long did the patient live?”: “Did the disease return?” or “Did any adverse event occur during treatment?” In clinical trials, the answers to these two questions are measured using Disease-Free Survival (DFS) and Event-Free Survival (EFS) , respectively.
DFS and EFS are two fundamental survival measures used to assess the effectiveness of cancer treatment early and quantitatively . These indicators reflect not only the length of survival, but also the treatment’s success in keeping the disease under control.
As oncology research has developed, particularly since the 2000s, DFS and EFS rateshave become primary or secondary endpoints for drug efficacy in phase III clinical trials. Agencies such as the FDA and EMA have also begun to accept these parameters as a “surrogate endpoint” in place of overall survival (OS).
1️⃣ Disease-Free Survival (DFS)
DFSis defined as “the period after a patient’s initial treatment during which the cancer does not return in any form.” This period continues until recurrence (local or distant), development of a new primary cancer or death occurs. In other words, it measures the period “without the disease returning” after the disease has been completely eliminated.
DFS is generally used in early-stage solid tumors completely resected by surgery (breast, colon, lung, kidney, endometrium) to measure the effectiveness of adjuvant therapies (chemotherapy, hormonal therapy, immunotherapy).
2️⃣ Event-Free Survival (EFS)
EFSis “the time from the start of treatment until any predefined adverse event occurs.” This event may be not only recurrence, but also treatment failure, progression, treatment discontinuation due to toxicity or death .
EFS is particularly preferred for neoadjuvant (preoperative) treatments and hematological malignancies (acute leukemia, lymphoma, non-Hodgkin lymphoma).
| Criterion | DFS | EFS |
|---|---|---|
| Start of Follow-Up | After treatment is completed | At the start of treatment |
| Endpoint Events | Recurrence, new tumor, death | Progression, treatment failure, recurrence, death |
| Typical Use | Early-stage solid tumors after adjuvant therapy | Neoadjuvant therapy or hematological cancers |
Where and Why Are They Used?
DFS and EFS are early indicators of the effectiveness of oncolytic therapies. These indicators make it possible to see how well a treatment controls the disease without waiting for long-term overall survival (OS) results.
- DFS: Measures the effectiveness of adjuvant therapies in early-stage breast, colon, lung and kidney cancers. The “time without recurrence” after surgery is considered critical.
- EFS: Measures whether treatments such as neoadjuvant chemotherapy/immunotherapy reduce adverse events such as disease progression, inability to proceed to surgery or interruption due to treatment toxicity.
- Regulatory perspective: In some drug approvals, the FDA and EMA evaluate DFS/EFS data as a “surrogate endpoint,” meaning an indicator of a survival benefit that will emerge later .
Clinical Examples
OlympiA Phase III trial (NEJM 2021) – In BRCA-mutant early-stage breast cancer, adjuvant Olaparibincreased 3-year DFS to 85.9% versus 77.1% with placebo (HR = 0.58; p < 0.001). This result showed that DFS reflects clinical benefit early.
ADAURA (Osimertinib) – NEJM 2020: In EGFR-positive stage IB–IIIA patients, adjuvant Osimertinib reduced DFS risk by 80% compared with placebo (HR = 0.20; p < 0.001). The DFS difference emerged 3 years before the overall survival difference.
KEYNOTE-671 – Lancet 2023: In the neoadjuvant + adjuvant Pembrolizumab regimen, EFS was defined as the primary endpoint . A significant advantage was found in the time without progression or until treatment discontinuation (HR = 0.58).
Importance in Clinical Trials
DFS and EFS are increasingly used as “primary endpoints” in phase III oncology trials. This is because measuring overall survival (OS) takes a long time and subsequent treatments affect the result.
- DFS generally measures the early effectiveness of adjuvant therapies; for example, it was the primary endpoint in the KEYNOTE-564 (renal cell carcinoma) and CheckMate-238 (melanoma) trials.
- EFS is a composite indicator of events such as treatment failure, relapse or death, particularly in hematological cancers (ALL, AML, lymphoma).
Why Do They Matter in Oncology?
In modern oncology, DFS and EFS are not merely academic metrics; they shape clinical decisions . High DFS/EFS rates indicate successful disease control, while low rates suggest that more aggressive or combined approaches are needed.
- For the physician: The answer to “How long does the disease remain under control?” determines follow-up frequency, imaging strategy and the need for additional treatment.
- For the patient: The question “Has the cancer returned or not?” turns an abstract statistic into a personal prognosis; it also matters in terms of psychological burden.
- For regulation: Regimens that show a DFS/EFS advantage offer an opportunity to intervene before the metastatic stage, potentially opening the door to earlier approval for some drugs.
DFS and EFSrepresent a third dimension of cancer treatment beyond “quality and length of life”: the dimension of “keeping the disease under control.” Both measures can indicate treatment success early and accelerate innovation in oncology.
However, it should be remembered that increases in DFS and EFS and overall survival (OS) may not always run in parallel. These data should therefore be interpreted in the context of biological meaning, disease stage and follow-up duration .
References
- National Cancer Institute. Definition of Disease-Free Survival & Event-Free Survival. cancer.gov (2024)
- Mauri D et al. “Disease-free survival as a surrogate for overall survival in adjuvant breast cancer trials.” J Natl Cancer Inst 2006; 98:182.
- Blumenthal GM et al. “Analysis of time to approval of oncology drugs with and without DFS/EFS as endpoints.” Clin Cancer Res 2019; 25:6059-6069.
- Wolchok JD et al. “Adjuvant Nivolumab in Resected Melanoma.” N Engl J Med 2021.
- ASCO Daily News. “Why DFS and EFS Matter in Clinical Trials.” 2024.
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