Endocrine Therapy, Stable Disease, and Dormancy in ER-Positive Breast Cancer
Why endocrine therapy can help hold ER-positive breast cancer in a long quiet phase, and why late reactivation can still happen
ER-positive breast cancer is one of the clearest dormancy settings in oncology.
Late relapse can happen many years after diagnosis.
That pattern fits with residual cells staying alive, but quiet, in places such as bone marrow.
Why ER-positive disease is different
ER-positive breast cancer has a long tail of recurrence risk.
That risk can continue for decades.
This is one reason dormancy matters so much in this subtype.
Researchers increasingly interpret this pattern as evidence of dormant disseminated tumour cells that survive initial treatment, remain scan-invisible, and later reactivate.
How endocrine therapy fits the dormancy picture
Endocrine therapy lowers estrogen signalling.
That includes tamoxifen, aromatase inhibitors, and ovarian suppression such as goserelin (Zoladex).
These treatments can shrink active disease.
They can also help push some residual ER-positive cells into a low-growth or dormant state.
That helps explain why some patients experience long periods of stable disease even when every last cell is probably not gone.
Some recent reviews now describe adjuvant endocrine therapy as one practical strategy for maintaining cellular dormancy in ER-positive disease.
Why relapse can still happen later
Dormancy is not the same as cure.
Estrogen deprivation affects more than the tumour cell.
It can also reshape the surrounding niche.
Experimental work suggests that bone-marrow stromal injury, stromal senescence, oxidative stress, hypoxic stress, and inflammatory cytokines such as IL-6 and IL-8 may help reawaken dormant ER-positive cells.
This offers one plausible explanation for a hard clinical pattern:
endocrine therapy helps hold disease quiet for years
residual cells remain too small to detect
a later biological shift allows regrowth
"Dormant cancer cells are like the embers left in an abandoned campfire, and respiratory viruses are like a strong wind that reignites the flames"
Respiratory viral infections awaken metastatic breast cancer cells in lung
Why this matters when disease looks small or stable
This is where dormancy thinking becomes practical.
A tiny stable focus is not always a simple "kill it now" problem.
Sometimes the more useful question is whether the current strategy is helping keep residual ER-positive cells suppressed.
That does not mean ignoring progression.
It means balancing eradication, long-term control, quality of life, and the risk of triggering a more inflammatory or disruptive environment.
Related dormancy pages
Bottom line
In ER-positive breast cancer, endocrine therapy can sometimes do more than shrink visible disease.
It may also help hold residual cells in dormancy.
That helps explain both long periods of stability and the possibility of very late relapse.
Key references
Reawakening of dormant estrogen-dependent human breast cancer cells by bone marrow stroma
https://pmc.ncbi.nlm.nih.gov/articles/PMC6098600/
Breast cancer dormancy: need for clinically relevant models to address late recurrence
https://www.nature.com/articles/s41523-021-00269-x
Dormancy and Recurrence in Breast Cancer Bone Metastasis
https://advanced.onlinelibrary.wiley.com/doi/10.1002/adbi.202500485