Hormones and Breast Cancer: Understanding the Connection
Dr. Vrundali Kannoth•5 minutes•16 Sep 2025
Hormonal Impact on Breast Cancer: Causes and Insights
Your hormones do a lot of heavy lifting. They shape your body, your mood, your sleep, and your cycle until someone brings up breast cancer. Then suddenly you're left wondering: could something so natural also be part of the problem? It’s confusing. Is it the oestrogen your body makes? The birth control pill you took in your 20s? You're not alone in wondering how all this connects.
With more people turning to hormone-based therapies and research evolving every year, the questions around hormones and breast cancer, as well as prevention, are only getting louder. Knowing how your choices interact with your body and your background puts you in a stronger position to decide what’s best for you.
Understanding hormones and breast cancer: What is the connection
Hormones are chemical messengers that regulate key functions in your body, such as growth, reproduction, metabolism, and more. When it comes to breast tissue, though, two hormones in particular, oestrogen and progesterone, play a major role. They help develop and maintain breast structure, especially during puberty, pregnancy, and your menstrual cycle.
But prolonged exposure to these hormones can increase the chance of abnormal cell growth. This can be through early menstruation, late menopause, hormonal imbalance, or external sources like hormone therapy. That’s where the concern around hormones and breast cancer comes in.
Roughly 7 in 10 breast cancers are hormone receptor-positive, meaning they develop in response to oestrogen, progesterone, or both. Hence why oncologists carefully evaluate hormones and breast cancer risk in people considering hormone therapies for concerns like birth control or menopause management.
They don’t evaluate just the presence of hormones, though; it’s also how long and how much your body has been exposed that matters. When you know this terrain, you can ask smarter questions and make decisions that truly fit your body and your life.
Hormone exposures linked to breast cancer: What to watch for
Not all hormones carry the same weight when it comes to breast cancer risk. Some come from inside your body, shaped by your life stage or reproductive history. Others are added from the outside, through birth control, hormone therapy, or supplements.
Here’s a breakdown of them all and what science says about their connection to hormones and breast cancer.
Endogenous exposure: When your own hormones raise risk
Your body makes its own hormones, especially oestrogen and progesterone, and for the most part, that’s a good thing. But when these hormones stick around for longer than usual, they may increase the likelihood of cell changes that can lead to breast cancer. That’s why oncologists pay close attention to factors that extend your lifetime exposure to oestrogen. For example:
- •Early menstruationmeans your ovaries start producing oestrogen sooner.
- •Late menopausemeans they keep doing it for longer.
- •No full-term pregnancymeans your oestrogen levels don’t get the natural breaks that happen during pregnancy.
- •Obesityadds another layer - fat tissue can produce oestrogen even after menopause.
All of these stretch your "oestrogen window,” or the total time your body is bathing in this hormone. The longer that window, the more chances abnormal cells have to grow in response. It’s not a guarantee, but it’s a well-documented link in hormone-related breast cancer risk, one you can manage better once you understand it.
Exogenous hormones: What we add from outside
Sometimes, the hormones affecting your body don’t originate from within. External or "exogenous" hormone use, like birth control or menopause therapy, can also influence hormones and breast cancer risk, especially depending on type, duration, and timing. Let’s look at the most commonly used hormone-based treatments and what current research says:
- •Contemporary hormonal contraceptionThese include modern options like the pill, hormonal IUDs, rings, or patches. A 2023 Plos Medicine study found a 20-30% increase in breast cancer risk, specifically with longer use. Still, the absolute risk remains low, and benefits often outweigh the risks for younger women.
- •Hormone replacement therapy (HRT)Used to ease menopause symptoms, HRT may include oestrogen-only or a combined oestrogen-progestin formula. The Women’s Health Initiative found that combined HRT was linked to a 24% higher breast cancer risk, while oestrogen-only HRT posed less concern, especially for those who’ve had a hysterectomy.
- •Bioidentical hormones and compounded therapyMarketed as “natural” or safer, these hormones are designed to mimic what your body already produces. They’re often used to ease menopause symptoms, but many are custom-mixed in compounding pharmacies, meaning dosage and quality can vary. They still impact hormone-sensitive breast tissue, and long-term safety data are limited. So caution is key.
Environmental hormones: how everyday chemicals quietly mess with your balance
You might not be taking hormone therapy, but your body still gets little hormonal nudges from the world around you. Environmental hormones, also known as endocrine disruptors, are found in things we use every day, such as plastic bottles, processed food packaging, synthetic fragrances, and even tap water. These chemicals mimic oestrogen and can bind to hormone receptors in breast tissue, potentially raising your breast cancer risk over time. Repeated exposure to EDCs like BPA (in plastic containers), parabens (in lotions and makeup), and phthalates (in synthetic fragrances) can throw off your body’s natural hormone balance. That’s a concern, especially for those already at higher hormones and breast cancer risk. While the link between environmental hormones and cancer is still being researched, it's something experts are paying attention to. Small lifestyle changes like using glass containers, reading product labels, and choosing unscented or clean-certified items can help reduce exposure and lower potential long-term risks.
What hormone-blocking therapies do and who they’re for
Once a breast cancer diagnosis is confirmed, hormones don’t stop being relevant. In fact, they become the blueprint for your treatment.
Oncologists test whether the tumour is hormone receptor-positive (ER+/PR+), meaning it feeds on oestrogen or progesterone. About 70% of breast cancers fall into this category.
They also assess for HER2/neu levels: a protein on breast cells that, when elevated, signals a HER2-positive cancer. These tend to grow and spread faster, while HER2-negative types behave more slowly.
In both cases, the goal is to cut off the tumour's fuel source, which is why breast cancer treatment often includes hormone therapy or targeted blockers.
Ultimately, whether you're premenopausal, postmenopausal, or at high risk of recurrence, your hormonal status helps determine which of the following treatments your oncologist may recommend:
- •TamoxifenUsed primarily in premenopausal women, Tamoxifen binds to oestrogen receptors in breast tissue and blocks the hormone’s ability to fuel cancer growth. It’s typically prescribed for 5-10 years and is known to lower the risk of both recurrence and developing cancer in the other breast.
- •Aromatase inhibitors (AIs)AIs, like letrozole, anastrozole, or exemestane, are used in postmenopausal women. They stop the body from converting androgens into oestrogen, drastically reducing oestrogen levels in the body. This helps slow or stop the growth of hormone-sensitive tumours.
- •Ovarian suppressionIn high-risk premenopausal patients, oncologists may recommend shutting down the ovaries’ hormone production using medication or surgery. This approach is often combined with other therapies to further reduce hormone-related breast cancer risk.
Cutting your risk: Hormone-related breast cancer factors you can control
While you can’t change when your periods started or your family history, there are things within your control when it comes to hormones and breast cancer. From the contraception you choose to how you manage menopause, small, informed choices can help reduce long-term risk.
- •Rethink hormone replacement therapy (HRT)If you’re considering HRT for menopause, talk to your oncology doctor about the lowest effective dose and duration. Studies show that combined HRT (oestrogen + progestin) may raise the risk more than oestrogen-only therapy.
- •Stay updated on contraception risksModern birth control options are safer than ever, but contemporary hormonal contraception and the risk of breast cancer are still being studied. If you're high-risk, ask your doctor if non-hormonal options might suit you better.
- •Address hormonal imbalance earlyUnexplained weight gain, irregular periods, or acne? These could be signs of hormonal imbalance, which some studies link to higher breast cancer risk. A check-in with your care team and a few blood tests could give you clarity.
- •Keep a healthy weight post-menopauseAfter menopause, oestrogen is produced in fat tissue. So higher body fat means higher oestrogen levels, which can increase the likelihood of hormone-sensitive cancers. Regular movement and balanced nutrition help lower this risk.
Making sense of hormone therapy, breast cancer risk, and your own history isn’t about fear; it’s about strategy. Ask, test, tweak. Because informed small steps today can reshape outcomes tomorrow.
Taking charge of your hormonal health to lower breast cancer risk
The link between hormones and breast cancer can feel overwhelming, but knowledge truly is power. From contemporary hormonal contraception to bioidentical hormone therapy, the choices we make for health, birth control, or menopause can shift risk without us even realising it. If you’re unsure where you stand, start with a proper hormonal assessment and routine breast screening. Knowing your hormone receptor status also plays a key role in shaping the right breast cancer therapy, including whether hormone-blocking treatments might work for you.
Take this as your nudge to book that screening. Talk to a trusted oncologist and get guidance tailored to your body and risk profile.
When in doubt,
FAQs on hormone therapy and breast cancer
Hormone therapy in breast cancer treatment works by blocking the hormones like oestrogen or progesterone that fuel certain tumours. If your cancer is hormone receptor-positive, this therapy can slow growth, lower the chance of recurrence, and support long-term recovery. It’s a key part of treatment for many people, especially postmenopause.
Hormone receptor-positive breast cancer is the most common hormone-driven type. These cancers grow in response to oestrogen or progesterone, which is why hormone therapy is often part of the treatment plan.
Oestrogen and progesterone are the key hormones linked to breast cancer risk. When your body is exposed to them for longer, like through early periods, late menopause, or external hormone use, it can increase risk. That's why hormonal imbalance and breast cancer are often studied together
Around 70% of breast cancers are hormone receptor-positive. These types respond well to hormone-blocking treatment and usually grow more slowly than other types.
Table of Content
- Hormonal Impact on Breast Cancer: Causes and Insights
- Understanding hormones and breast cancer: What is the connection
- Hormone exposures linked to breast cancer: What to watch for
- Environmental hormones: how everyday chemicals quietly mess with your balance
- What hormone-blocking therapies do and who they’re for
- Cutting your risk: Hormone-related breast cancer factors you can control
- Taking charge of your hormonal health to lower breast cancer risk