Short answer: The abbreviations that cause the most confusion in hematology and oncology are the ones that look alike but measure different things: overall survival (OS), progression-free survival (PFS), disease-free survival (DFS) and event-free survival (EFS); response categories (CR, PR, SD, PD) and how they feed the overall response rate (ORR); and shared acronyms such as PR (partial response vs progesterone receptor), HR (hazard ratio vs hormone receptor) and TTP (time to progression vs thrombotic thrombocytopenic purpura). This glossary defines the terms trainees meet most often in trials, tumor boards and board exams, grouped by use.
Author and disclosure: Roupen Odabashian, MD, FRCPC, Oncologist and founder of MeDucation AI. I am the founder of MeDucation AI, which sells hematology and oncology board preparation. I have no other financial relationships relevant to the topics discussed here. This article is educational and is not a substitute for individualized clinical judgment or tumor board discussion.
What do the survival endpoint abbreviations mean?
Abbreviation | Meaning | Definition |
|---|---|---|
OS | Overall survival | Time from diagnosis, randomization or the start of treatment until death from any cause |
PFS | Progression-free survival | Time from randomization to disease progression or death |
DFS | Disease-free survival | Time from randomization or definitive treatment to disease recurrence, progression or death from any cause, as defined in the protocol |
EFS | Event-free survival | Time after primary treatment during which the patient remains free of the specified events the therapy was designed to prevent or delay |
DoR | Duration of response | Time from the first documented partial or complete response to progression or death |
TTP | Time to progression | Time to progression, with deaths usually censored rather than counted as events |
The practical difference is that PFS counts death as an event, while TTP typically does not, and DFS applies to patients who are rendered free of disease by surgery or definitive therapy, whereas PFS applies when disease is still measurable. Always check how a trial defines its events in the protocol.
What do the response abbreviations mean?
Abbreviation | Meaning | Definition or note |
|---|---|---|
CR | Complete response | Disappearance of all signs of cancer, as defined by the response criteria used |
PR | Partial response | A predefined reduction in disease burden that does not meet criteria for CR |
SD | Stable disease | Cancer neither significantly shrinking nor growing |
PD | Progressive disease | Growth or spread meeting the progression criteria of the trial |
ORR | Overall or objective response rate | Percentage of patients with a partial or complete response |
MRD | Minimal residual disease | A small number of malignant cells that remain after treatment, below the detection limit of conventional morphology |
uMRD | Undetectable MRD | No detectable disease by a specified assay at a defined sensitivity threshold |
sCR | Stringent complete response | A deeper category of complete response used in multiple myeloma |
VGPR | Very good partial response | A myeloma response category between PR and CR |
CRi | Complete response with incomplete count recovery | A leukemia response category used in AML |
Response categories depend on the disease. Lymphoma, solid tumors, myeloma and leukemia each use different response criteria, so a CR in one setting is not defined the same way as in another.
What do performance status and toxicity grading mean?
Scale | Meaning |
|---|---|
ECOG 0 | Fully active, no restriction |
ECOG 1 | Restricted in strenuous activity but able to do light or sedentary work |
ECOG 2 | Ambulatory and capable of self-care but unable to work; up and about more than half of waking hours |
ECOG 3 | Capable of only limited self-care; in bed or a chair more than half of waking hours |
ECOG 4 | Completely disabled; confined to a bed or chair |
ECOG 5 | Death |
CTCAE grade 1 | Mild; asymptomatic or mild symptoms, no intervention needed |
CTCAE grade 2 | Moderate; minimal, local or noninvasive intervention indicated |
CTCAE grade 3 | Severe or medically significant but not immediately life-threatening; hospitalization indicated |
CTCAE grade 4 | Life-threatening; urgent intervention indicated |
CTCAE grade 5 | Death related to the adverse event |
ECOG performance status was described by Oken and colleagues in 1982. CTCAE, the Common Terminology Criteria for Adverse Events, is maintained by the National Cancer Institute, and version 5.0 was published in November 2017. Not every grade applies to every adverse event, so some terms list fewer than five grades.
What do common regimen abbreviations stand for?
Regimen | Components |
|---|---|
R-CHOP | Rituximab, cyclophosphamide, doxorubicin (hydroxydaunorubicin), vincristine (Oncovin), prednisone |
ABVD | Doxorubicin (Adriamycin), bleomycin, vinblastine, dacarbazine |
BEACOPP | Bleomycin, etoposide, doxorubicin (Adriamycin), cyclophosphamide, vincristine (Oncovin), procarbazine, prednisone |
GemOx / R-GemOx | Gemcitabine and oxaliplatin, with or without rituximab |
RVd or VRd | Lenalidomide (Revlimid), bortezomib (Velcade), dexamethasone; D-RVd adds daratumumab |
7+3 | Cytarabine for 7 days with an anthracycline for 3 days, the standard AML induction backbone |
FOLFOX | Folinic acid (leucovorin), fluorouracil, oxaliplatin |
FOLFIRI | Folinic acid (leucovorin), fluorouracil, irinotecan |
FOLFIRINOX | Folinic acid (leucovorin), fluorouracil, irinotecan, oxaliplatin |
AC-T | Doxorubicin and cyclophosphamide followed by a taxane, a common breast cancer sequence |
What do disease, biomarker and treatment-class abbreviations mean?
Abbreviation | Meaning |
|---|---|
AML, ALL, CLL, CML | Acute myeloid leukemia, acute lymphoblastic leukemia, chronic lymphocytic leukemia, chronic myeloid leukemia |
APL | Acute promyelocytic leukemia, treated with ATRA (all-trans retinoic acid) |
DLBCL, FL | Diffuse large B-cell lymphoma, follicular lymphoma |
MM, MGUS | Multiple myeloma, monoclonal gammopathy of undetermined significance |
MDS, MPN, CMML | Myelodysplastic syndromes, myeloproliferative neoplasms, chronic myelomonocytic leukemia |
TKI | Tyrosine kinase inhibitor |
ICI | Immune checkpoint inhibitor, such as a PD-1 or PD-L1 antibody |
CAR-T | Chimeric antigen receptor T-cell therapy |
ASCT or auto-HCT | Autologous stem cell transplant |
Allo-HCT | Allogeneic hematopoietic cell transplant |
GVHD | Graft-versus-host disease |
MSI-H, dMMR | Microsatellite instability high, deficient mismatch repair |
TMB | Tumor mutational burden |
ctDNA | Circulating tumor DNA |
What do oncologic emergency and complication abbreviations mean?
Abbreviation | Meaning |
|---|---|
CRS | Cytokine release syndrome, seen with CAR-T cells and bispecific antibodies |
ICANS | Immune effector cell-associated neurotoxicity syndrome |
TLS | Tumor lysis syndrome |
FN | Febrile neutropenia |
ANC | Absolute neutrophil count |
DIC | Disseminated intravascular coagulation |
HLH | Hemophagocytic lymphohistiocytosis |
TTP, HUS | Thrombotic thrombocytopenic purpura, hemolytic uremic syndrome |
HIT | Heparin-induced thrombocytopenia |
VTE | Venous thromboembolism |
Which abbreviations are easy to confuse?
PR can mean partial response or progesterone receptor, and the meaning depends entirely on context.
HR can mean hazard ratio in a trial or hormone receptor in breast cancer, and a trial can report a hazard ratio in a hormone receptor positive population in the same paragraph.
PD can mean progressive disease, while PD-1 and PD-L1 refer to the programmed death pathway.
TTP can mean time to progression in a trial or thrombotic thrombocytopenic purpura in the hematology clinic.
CR means complete response, but whether it requires a negative bone marrow, imaging or immunofixation depends on the disease and the criteria used.
To practice these distinctions in context, see Oncology Board Review Question Banks Compared or the broader plan in How to Pass the ABIM Medical Oncology Boards. For the full exam approach, read Oncology Board Review 2026.
Frequently asked questions
What is the difference between PFS and DFS?
PFS is measured from randomization to progression or death and is used when disease is still present. DFS is used after definitive treatment has left no detectable disease and counts recurrence, progression or death.
What does ORR mean in oncology?
ORR is the overall or objective response rate, the percentage of patients who achieve a partial or complete response.
What does ECOG performance status measure?
It grades a patient's functional status from 0, fully active, to 5, death, and is widely used to decide treatment eligibility and trial enrollment.
What does MRD negative mean?
MRD negative means no residual disease was detected by a specified assay at a defined sensitivity threshold, which does not mean that disease has been eliminated.
What is the difference between CRS and ICANS?
CRS is a systemic inflammatory syndrome with fever and hypotension, whereas ICANS is neurotoxicity after immune effector cell therapies. Both can occur with CAR-T cells and bispecific antibodies.
References
HemOnc.org. Glossary of hematology and oncology terms. hemonc.org
Oken MM, Creech RH, Tormey DC, et al. Toxicity and response criteria of the Eastern Cooperative Oncology Group. Am J Clin Oncol. 1982;5:649 to 655. ECOG performance status summary: depts.washington.edu
National Cancer Institute. Common Terminology Criteria for Adverse Events (CTCAE) version 5.0. November 27, 2017. dctd.cancer.gov
