Breast Cancer Awareness Month: Why It Starts, What to Look For, and What Screening Actually Covers

What actually causes breast cancer to start?

Breast cancer begins inside the milk ducts or the milk-producing lobules of the breast, when cells accumulate enough changes in the genes that normally control growth, repair and cell death to start dividing without the usual limits. As with other cancers, this is generally a biological process that unfolds over years rather than the result of one identifiable event, a stressful season, or a single lifestyle choice.

What determines an individual woman’s risk is a combination of factors that are not modifiable and factors that are. The HSE groups these clearly. Non-modifiable factors include age — risk increases as you get older, and most breast cancers occur in women over 50 — family history of breast cancer in a close relative, inherited changes in the BRCA1 or BRCA2 genes, denser breast tissue (which is more common in younger women), and a personal history of breast cancer or certain abnormal cell changes.

Hormonal exposure also plays a role, because oestrogen can influence how breast tissue behaves over a lifetime. The HSE lists earlier puberty, later menopause, having a first pregnancy after 30, and never having been pregnant as factors associated with greater lifetime oestrogen exposure and therefore a modest increase in risk. Combined hormone replacement therapy carries a slightly increased risk while it is used, and the contraceptive pill carries a small increased risk that returns to baseline roughly ten years after stopping.

Then there are the factors you can influence. Body weight matters specifically after menopause: a BMI of 30 or higher in postmenopausal women increases risk, largely because fat tissue becomes a source of oestrogen production once the ovaries stop producing it. Regular alcohol consumption and smoking both raise risk, in a dose-related way. None of these single-handedly determines an individual’s outcome, but together they are the levers a woman genuinely has some control over.

Which symptoms actually matter, and which ones don’t?

The HSE describes a new lump or an area of thickened tissue in the breast as the single most important sign to have checked. Alongside that, the recognised symptoms include a change in the size or shape of one or both breasts, bloodstained discharge from either nipple, a lump or swelling in either armpit, dimpling of the skin on the breast, a rash on or around the nipple, and a nipple that becomes sunken or pulled inward.

One point surprises almost every patient I share it with: breast pain is not usually a symptom of breast cancer. Cyclical tenderness linked to your menstrual cycle, and even some non-cyclical breast pain, is common and usually has a benign explanation. That does not mean pain should be ignored if it is new, persistent and localised to one spot, but pain alone, without a lump or visible change, is rarely the presenting sign of cancer.

Does a family history of breast cancer mean I will get it too?

Not necessarily, and this is one of the most important distinctions in the conversation. Most breast cancers are not caused by an inherited gene change. Where a family history does matter is in the pattern: which relatives were affected, whether they were on the same side of the family, how young they were at diagnosis, and whether ovarian cancer also appears in the family, since BRCA1 and BRCA2 changes raise the risk of both.

A woman who carries a harmful BRCA1 or BRCA2 mutation faces a substantially higher lifetime risk — the HSE describes this as up to a 6 in 10 to 8 in 10 chance by age 80 — compared with roughly 1 in 7 for women overall. That is a meaningfully different risk category, and it changes the conversation about screening frequency, starting age, and whether genetic counselling and testing are appropriate.

What I would ask any patient to do is bring the details, not just a yes or no. “My aunt had breast cancer” and “my mother and maternal grandmother were both diagnosed before 45” are two completely different pieces of information, and only one of them typically changes a screening recommendation.

What does BreastCheck actually screen, and who is eligible?

BreastCheck is Ireland’s national breast screening programme, and it currently invites women aged 50 to 69 who have no symptoms for a free mammogram every two years. This age range was set based on international evidence about where screening delivers the clearest balance of benefit against harm.

That range is under active review. The National Screening Advisory Committee has been asked to examine the evidence for extending the programme to women aged 45 to 49 and 70 to 74, in line with recent European guideline recommendations, though any expansion depends on demonstrating that the benefits would outweigh the harms and would meaningfully reduce breast cancer deaths in Ireland. Screening eligibility is one of the details in this article most likely to change, so always check the current BreastCheck and HSE guidance directly before assuming an age cutoff.

It is also worth understanding what mammography does and does not do well. It is very effective at finding change in typical breast tissue, but denser breast tissue — more common in younger women — can make mammograms harder to interpret, which is one reason screening is not simply extended to every age group without evidence of net benefit.

I’m under 50, or over 69 — does that mean I’m not at risk?

No. Screening age ranges are a population-level tool, built around where mammography delivers the best overall balance of benefit and risk across large numbers of women. They are not a statement that risk begins at 50 and ends at 69.

If you are younger than the screening age, your risk is generally lower, but it is not zero, and any new symptom — a lump, a skin change, nipple discharge — deserves assessment regardless of your age. If you are older than the screening age, the same applies: breast cancer risk does not fall to zero once BreastCheck invitations stop, so self-awareness needs to continue for life, not just for the years you are formally screened.

How do I actually check my own breasts, and what am I looking for?

The most useful approach is not a rigid monthly ritual performed the same way every time. It is genuine familiarity with your own breasts — how they normally look and feel — so that a real change stands out against that baseline rather than against a generic checklist.

In practice, that means looking at your breasts in the mirror occasionally, noting their usual size, shape and the position of your nipples, and feeling them with the flat of your fingers, including up into the armpit, at a time in your cycle when they are least tender if you still have periods. What you are looking and feeling for is a change from your own normal: a new lump, an area that feels thicker than the surrounding tissue, a change in shape or skin texture, or nipple changes such as discharge or inversion.

One normal-feeling lump discovered once is far less informative than noticing that something has changed since last time. That is the entire purpose of familiarity: it turns a vague worry into a specific, describable change you can bring to a clinician.

What happens if I find something that needs to be checked?

The pathway is designed to answer the question efficiently, not to alarm you at every step. It typically begins with a clinical history and a physical examination, followed by imaging — usually a mammogram, an ultrasound, or both — depending on your age and what the examination finds. If imaging shows something that needs further characterisation, a biopsy may be taken: a small tissue sample is removed and examined under a microscope by a pathologist.

Only if that pathway confirms cancer does the conversation move to staging — establishing how far, if at all, the disease has spread — and referral into specialist oncology care for treatment planning, which can include surgery, radiotherapy or systemic therapy depending on the type and stage.

At EC Clinic in Dublin, that conversation usually begins with a consulta ginecológica geral. For related awareness reading, see our guide to gynaecological cancer symptoms in Ireland, and our sensibilização para o cancro da mama information page.

Can I actually lower my risk?

Partly, yes. You cannot change your age, your genetics or your family history, but several genuinely modifiable factors are worth taking seriously: maintaining a healthy weight after menopause, since excess weight becomes a more significant oestrogen source once the ovaries stop producing it; limiting alcohol, since risk rises with the amount consumed; staying physically active; and not smoking.

None of these guarantees anything in either direction — women with no risk factors are diagnosed, and women with several risk factors never are. But they are the levers within your control, and knowing your family history well enough to flag it early is arguably just as valuable as any single lifestyle change, because it is what determines whether earlier or more frequent screening should even be on the table.

Medically reviewed by Dr. Eliana Castañeda, Obstetrician-Gynaecologist and Aesthetic Specialist · 2 October 2026

— Dra. Eliana Castañeda
Obstetrician-Gynaecologist and Aesthetic Specialist · Medical Director, EC Clinic Dublin · 22+ years of clinical practice across Venezuela, Spain and Ireland