Cyclin-Dependent Kinase Inhibition in Hormone-Receptor-Positive Breast Cancer

Hormone-receptor-positive breast cancer, characterised by oestrogen or progesterone receptor expression, often relies on cyclin-dependent kinases 4 and 6 (CDK4/6) to drive cell cycle progression through the G1–S transition. Binding of cyclin D to CDK4/6 leads to phosphorylation of the retinoblastoma protein (Rb), releasing E2F transcription factors and promoting DNA synthesis. Dysregulation of this pathway is a hallmark of luminal breast cancers and contributes to resistance to endocrine therapies. Selective inhibitors of CDK4/6 have been developed to preserve endocrine sensitivity by reinforcing Rb-mediated cell cycle arrest, delaying progression and extending clinical benefit. Moreover, therapeutic strategies now explore combination approaches with aromatase inhibitors, selective oestrogen receptor degraders and targeted agents, aiming to overcome intrinsic and acquired resistance while maintaining quality of life.

Research from Nature Portfolio

Recent studies have revealed that CDK4/6 activity remains crucial beyond G1 phase, sustaining cyclin A2–CDK2 function throughout S and G2. Interruption of CDK4/6 not only induces G1 arrest but can precipitate reversal of cell cycle commitment if mitotic entry is delayed, underscoring a broader temporal window for therapeutic intervention.

Advances in biomarker development have demonstrated that early changes in circulating tumour DNA (ctDNA), particularly PIK3CA mutation levels, predict response to combined CDK4/6 inhibition and endocrine therapy. Rapid declines in ctDNA correlate with prolonged progression-free intervals, suggesting that ctDNA dynamics can serve as an early indicator of drug efficacy and clonal evolution under treatment pressure.

Cyclin-Dependent Kinase Inhibition in Hormone-Receptor-Positive Breast Cancer publication trend

The graph below shows the total number of articles in cyclin-dependent kinase inhibition in hormone-receptor-positive breast cancer across all publications each year (not limited to Nature Index journals).

Technical terms

Cyclin-dependent kinases (CDKs): Enzymes that, when bound to specific cyclins, phosphorylate target proteins to regulate cell cycle transitions.

Retinoblastoma protein (Rb): A tumour suppressor that, when unphosphorylated, inhibits E2F transcription factors and prevents cell cycle progression.

Cyclin D: Regulatory subunit that binds CDK4/6 to initiate phosphorylation of Rb and drive the G1–S transition.

Hormone-receptor-positive: Breast cancer subtype expressing oestrogen and/or progesterone receptors, often responsive to endocrine therapies.

Circulating tumour DNA (ctDNA): Fragments of tumour-derived DNA in the bloodstream used as a non-invasive biomarker to monitor treatment response and tumour evolution.

References

1. Loss of CDK4/6 activity in S/G2 phase leads to cell cycle reversal. Nature (2023).
2. MONARCH 3 final PFS: a randomized study of abemaciclib as initial therapy for advanced breast cancer. npj Breast Cancer (2019).
3. Early circulating tumor DNA dynamics and clonal selection with palbociclib and fulvestrant for breast cancer. Nature Communications (2018).