# Molecular response (MMR, MR4, treatment-free remission)

Source: https://onco.cc/terms/molecular-response/  
OnCo record `molecular-response` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

In chronic myeloid leukaemia, how far the leukaemia gene signal in the blood has fallen, measured in logs: a 1,000-fold drop is a major molecular response, a 10,000-fold drop (MR4) is 'deep'. Deep responses held for two years let some patients stop their pills.

## Summary

Quantitative PCR for BCR::ABL1 transcripts on the International Scale defines milestones: ≤10% at 3 months (early molecular response), ≤1% (complete cytogenetic response equivalent), ≤0.1% (MMR) by 12 months, ≤0.01% (MR4) and ≤0.0032% (MR4.5). Missing milestones triggers a switch of TKI. Sustained deep response for at least two years permits a supervised stop; about half stay in treatment-free remission and the rest regain response on restarting (EURO-SKI). 'Molecular relapse' is a rising transcript before any clinical sign. The concept is being borrowed for ctDNA-guided stopping in solid tumours.

## Fields

- Kind: Term
- Last checked: 2026-09-09
- Also known as: major molecular response; MR4; MR4.5; deep molecular response; complete molecular response; BCR-ABL1 transcript; BCR::ABL1 IS; International Scale; treatment-free remission; TFR; molecular relapse; cytogenetic response; complete cytogenetic response; early molecular response; cytogenetic responses; molecular responses

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Chronic_myelogenous_leukemia
- Wikipedia: https://en.wikipedia.org/wiki/Chronic_myelogenous_leukemia

## Connected records

- terms: [BCR::ABL1 kinase domain mutations (T315I and others)](https://onco.cc/terms/abl1-kinase-domain-mutations/), [Fixed-duration vs continuous therapy](https://onco.cc/terms/fixed-duration/), [MPN driver mutations (JAK2 V617F, CALR, MPL) and allele burden](https://onco.cc/terms/mpn-driver-mutations/), [Philadelphia chromosome (Ph+, BCR::ABL1)](https://onco.cc/terms/philadelphia-chromosome/), [Sokal and ELTS risk scores (chronic myeloid leukaemia)](https://onco.cc/terms/sokal-elts-scores/), [Tyrosine kinase inhibitor (TKI)](https://onco.cc/terms/tki-term/), [Undetectable MRD (uMRD / MRD-negative)](https://onco.cc/terms/umrd/)
- fronts: [Diagnostics & Biomarkers](https://onco.cc/fronts/diagnostics/), [Targeted Therapy](https://onco.cc/fronts/targeted-therapy/)
- drugs: [Asciminib](https://onco.cc/drugs/asciminib/), [Dasatinib](https://onco.cc/drugs/dasatinib/), [Imatinib](https://onco.cc/drugs/imatinib/), [Nilotinib](https://onco.cc/drugs/nilotinib/)
- cancers: [Advanced systemic mastocytosis (aggressive SM, SM with an associated haematological neoplasm, mast cell leukaemia)](https://onco.cc/cancers/advanced-systemic-mastocytosis/), [Chronic myeloid leukaemia, chronic phase](https://onco.cc/cancers/cml-chronic-phase/), [Indolent and smouldering systemic mastocytosis](https://onco.cc/cancers/indolent-systemic-mastocytosis/), [Systemic mastocytosis](https://onco.cc/cancers/systemic-mastocytosis/)
- biomarkers: [BCR::ABL1 transcript (Philadelphia chromosome, quantitative PCR)](https://onco.cc/biomarkers/bcr-abl1-transcript/), [NPM1 mutation](https://onco.cc/biomarkers/npm1-mutation/)

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