10/17/2026
When I was diagnosed with breast cancer in July, I was doing quite a lot of research on it, and this was one of the things that I didn’t understand was why I would have to be on a pill after I had my mastectomy. A pill that I would have to take every day for such a long time. Finally, this article explains exactly why I will need to do that. I was diagnosed with invasive ductal carcinoma, and it is not hereditary, and it was only discovered on a visual inspection of my breast, not on a self exam. Because of the location, my chances of discovering it on the self exam would’ve been extremely slim. So not only is it important for mammograms to be conducted annually, but always do a visual inspection in the mirror no matter how old you are because any changes to the breast can be a change that affects you for the rest of your life, including your family. 
Kelly
💗💗💗
Imagine a woman of 58 who finishes surgery for breast cancer, hears that the tumour is out, and quietly wonders why she now has to take a tablet every day for five years.
The answer sits in the biology of the most common type of breast cancer, the one called hormone receptor positive. In a large US cancer registry, about 73% of breast cancers with known receptor results were hormone receptor positive and HER2 negative.
If you or someone you love has this diagnosis, this post explains what is happening inside the body and what the evidence says genuinely helps.
WHAT THE LABEL MEANS
Every breast cancer is tested for receptors, small docking stations that respond to hormones. Testing guidance from ASCO and the College of American Pathologists calls a cancer oestrogen receptor positive when 1% or more of its cell nuclei carry the receptor.
Results from 1% to 10% are reported as ER Low Positive, because the benefit of hormone therapy in that band is less certain. A positive result means the cancer uses oestrogen as fuel.
THE BREAST MAKES ITS OWN OESTROGEN
Many people assume that after menopause oestrogen disappears. It does fall in the blood. But the fat inside the breast carries an enzyme called aromatase that keeps making oestrogen right next to the tumour.
A scientific review of oestrogen sources found that oestrogen inside a breast tumour can reach at least ten times the level in the blood. The tumour even encourages this. It releases a signalling molecule, prostaglandin E2, that pushes the nearby fat to make more aromatase.
FROM SIGNAL TO CELL DIVISION
When oestrogen reaches the cancer cell, it binds the receptor. The receptor then switches on growth genes. One key step is a checkpoint where the cell decides whether to copy its DNA and divide. Two enzymes, CDK4 and CDK6, control that checkpoint in this cancer.
Newer tablets called CDK4/6 inhibitors target exactly that step.
Over time, some cancers adapt. In one study of tumours that had spread, 14 of 80 carried changes in the receptor gene itself. These altered receptors switched on growth even without oestrogen. This helps explain why a medicine can work for years and then lose its effect, and why doctors keep developing new options.
WHY THE TABLETS MATTER AFTER SURGERY
Surgery removes the visible tumour. It cannot remove a few stray cells that may have travelled. Those cells still respond to oestrogen.
A pooled analysis of 20 trials and 21,457 women showed that about five years of tamoxifen cut recurrence nearly in half during the first five years and by about a third in the five years after the tablets stopped. Breast cancer deaths fell by about a third over 15 years.
After menopause, aromatase inhibitors such as anastrozole, letrozole and exemestane block the enzyme that makes local oestrogen. In 31,920 postmenopausal women they lowered recurrence by about 30% compared with tamoxifen while the treatments differed.
Before menopause, adding treatment that switches off the ovaries improved results for higher risk women. In the SOFT trial, eight year disease free survival rose from 78.9% with tamoxifen alone to 85.9% with exemestane plus ovarian suppression.
For people at high risk, adding two years of abemaciclib, a CDK4/6 inhibitor, raised four year invasive disease free survival from 79.4% to 85.8% in a trial of 5,637 patients.
HORMONE THERAPY COMES FIRST
For this cancer, hormone therapy is the essential first line treatment. NICE guidance from 2018 recommends an aromatase inhibitor as the first hormone treatment for postmenopausal women with oestrogen receptor positive cancer who are not at low risk, with tamoxifen when an aromatase inhibitor does not suit. Food, exercise and supplements support recovery. They never replace this medicine.
THE LONG TAIL
This cancer can come back late. In 62,923 women who were well after five years of hormone therapy, recurrences kept appearing at a steady rate from year 5 to year 20. The risk of distant recurrence ranged from about 10% to 41%, depending on tumour size, lymph nodes and grade. Follow up is a long partnership, not a single appointment.
TAKING IT EVERY DAY IS PART OF THE TREATMENT
In a cohort of 8,769 women, 31% stopped hormone therapy early. Ten year survival was 80.7% for women who continued and 73.6% for those who stopped. Side effects such as joint aches and hot flushes are worth raising with the prescriber, who manages any change to the plan.
A MEDICINE CHECK THAT COULD MATTER
Tamoxifen must be activated by a liver enzyme called CYP2D6. Some medicines block that enzyme. In a population study of older women on tamoxifen, the antidepressant paroxetine was linked with a higher risk of breast cancer death, rising with how long the two overlapped. Other antidepressants did not show this. Antidepressants, blood thinners and many other medicines deserve a pharmacist review alongside tamoxifen. Any change is a decision for the prescriber.
Aromatase inhibitors can thin the bones. Five year fracture risk was 8.2% with aromatase inhibitors against 5.5% with tamoxifen. Expert bone guidance advises a fracture risk check, exercise advice, and calcium and vitamin D when an aromatase inhibitor begins, with the amounts set by the clinician.
FOOD AND DAILY HABITS, WHAT THE EVIDENCE SAYS
A large trial of 3,088 survivors tested a diet very high in vegetables, fruit and fibre and low in fat. After 7.3 years, about 17% of women in both groups had a new breast cancer event. Diet alone did not change recurrence.
Soy often worries people. In a Shanghai cohort of 5,042 survivors, women eating the most soy food had lower death and recurrence rates, including women with oestrogen receptor positive cancer and women taking tamoxifen. This was soy food, not concentrated supplements.
Movement shows the clearest link. Across 22 cohort studies, physical activity after diagnosis was associated with 41% lower breast cancer mortality. Weight gain after diagnosis was linked with higher breast cancer mortality. These are associations, not proof, yet they fit the biology, since fat tissue makes oestrogen after menopause.
A SIMPLE CARD TO SHARE
Five questions worth taking to the next appointment.
#1 - What is my oestrogen receptor percentage?
#2 - Which hormone therapy fits my menopausal status, and for how long?
#3 - Do I need a bone density check?
#4 - Do any of my medicines affect tamoxifen?
#5 - Which side effects should I report straight away?
If someone in your circle was recently diagnosed, these five questions may make their next visit easier. Feel free to pass them on.
WARNING SIGNS THAT NEED PROMPT CARE
- A new lump.
- Bone pain that persists.
- Chest pain or shortness of breath.
- Ongoing abdominal pain.
- Persistent headaches.
For anyone on tamoxifen, a swollen painful leg, sudden breathlessness or unexpected vaginal bleeding needs urgent attention.
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Prepared by Edward Paul Mshani, BPharm
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Disclaimer
This content is for educational purposes only and does not constitute medical advice, diagnosis or treatment. Do not stop, start or modify any prescribed medication or supplement regimen without consulting a qualified healthcare professional. Individual clinical decisions require personalised medical assessment.
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Sources
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Tier 1, human clinical trials and meta analyses
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Early Breast Cancer Trialists' Collaborative Group (EBCTCG); Davies C, et al. Relevance of breast cancer hormone receptors and other factors to the efficacy of adjuvant tamoxifen: patient-level meta-analysis of randomised trials. Lancet. 2011 Aug 27;378(9793):771-84. doi: 10.1016/S0140-6736(11)60993-8. Epub 2011 Jul 28. PMID: 21802721; PMCID: PMC3163848.
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