What Is Mammography?
Mammography is specialised X-ray imaging of the breast. It is the only screening test proven in randomised controlled trials to reduce breast cancer mortality. In a mammogram, the breast is gently but firmly compressed between two plates to spread the tissue, reducing X-ray dose and producing a clearer image. Two views are taken of each breast — craniocaudal (top-to-bottom) and mediolateral oblique (angled from the side).
Mammography detects structural changes in breast tissue, including masses, calcifications (small calcium deposits that can signal early cancer), and distortions of the normal architecture. Not all abnormalities found on mammography are cancer — most recalled women do not have cancer.
Key Points
- Mammography is the only population screening tool proven to reduce breast cancer death.
- Routine screening mammography is recommended every 2 years for women aged 50–74 in Australia.
- Most abnormal screening mammograms do not indicate cancer — recall for additional imaging is common.
- Dense breast tissue reduces mammography sensitivity and is an independent risk factor for breast cancer.
- BI-RADS is the standardised system for reporting mammography findings.
- Women with a strong family history or known BRCA pathogenic variants need individualised surveillance.
- Any new breast symptom (lump, discharge, skin change) requires prompt GP assessment — do not wait for scheduled screening.
Screening vs Diagnostic Mammography
| Screening | Diagnostic | |
|---|---|---|
| Who | Asymptomatic women | Women with a specific breast concern |
| Why | Detect cancer before symptoms | Investigate a clinical finding |
| Views | Standard (2 views per breast) | Additional/targeted views as needed |
| Additional imaging | May follow if recall | Often includes ultrasound |
| How organised | Population programme (BreastScreen) | Referred by GP or specialist |
Screening mammography is a population-level programme — it applies a test to women without symptoms to catch cancer early. Diagnostic mammography is arranged when there is something specific to investigate.
If you have a breast concern, see your GP for a referral to diagnostic imaging, rather than attending a screening programme.
Age and Screening Recommendations (Australia)
| Age | Recommendation |
|---|---|
| Under 40 | Not recommended for average-risk women; risk-benefit balance does not favour routine screening |
| 40–49 | Can self-refer to BreastScreen; not actively invited; benefits and harms should be discussed individually |
| 50–74 | Recommended every 2 years; actively invited through BreastScreen Australia |
| 75+ | Can self-refer; no upper age limit; individual decision based on health and life expectancy |
| High risk (BRCA, strong family history) | Individualised plan, usually starting earlier and often including breast MRI |
Age recommendations reflect the balance between benefits (mortality reduction) and harms (false positives, overdiagnosis, radiation) at different ages. Younger women have denser breasts (reducing mammography sensitivity), a higher baseline rate of benign findings, and longer exposure to any potential radiation risk.
Understanding BI-RADS Results
BI-RADS (Breast Imaging Reporting and Data System) is the standardised reporting framework used by radiologists worldwide.
| BI-RADS Category | Meaning | What Typically Follows |
|---|---|---|
| 0 — Incomplete | Additional imaging needed before a final assessment | Recall for extra views, ultrasound |
| 1 — Negative | No significant abnormality | Routine next screening |
| 2 — Benign | Definitely benign finding (e.g., cyst, calcification pattern that is clearly benign) | Routine next screening |
| 3 — Probably benign | Short-term follow-up recommended | Repeat imaging at 6 months |
| 4 — Suspicious | Biopsy generally recommended | Tissue sampling |
| 5 — Highly suspicious | High probability of malignancy | Biopsy before treatment planning |
| 6 — Known malignancy | Biopsy-proven cancer | Treatment planning |
Most screening mammograms return a Category 1 or 2 result. A Category 0 recall is common from screening and most often resolves to a benign finding with additional imaging.
Dense Breasts
Breast tissue is classified into four density categories on mammography:
- A (almost entirely fatty) — ~10% of women
- B (scattered fibroglandular) — ~40%
- C (heterogeneously dense) — ~40%
- D (extremely dense) — ~10%
Dense tissue (categories C and D) matters for two reasons:
- Masking effect — dense tissue and tumour both appear white on mammography, reducing sensitivity. Studies suggest mammography misses 25–50% of cancers in women with extremely dense breasts.
- Independent risk factor — high breast density is associated with a 4–6 fold increase in breast cancer risk compared with low density.
Women with dense breasts may be advised to discuss supplemental screening options — typically breast ultrasound, or MRI for very high-risk women — with their doctor. Australia does not currently have a national programme for supplemental dense-breast screening, but it is an active area of discussion.
False Positives and Overdiagnosis
False positives are abnormal mammogram findings that turn out not to be cancer. Over a decade of biennial screening:
- Approximately 1 in 10 women will be recalled for additional imaging at some point
- Around 1 in 100 will have a biopsy that returns a benign result
False positives cause anxiety, additional procedures, and costs — and are a recognised harm of screening. Recall rates vary between programmes.
Overdiagnosis refers to the detection and treatment of cancers that would never have caused symptoms or death in the person’s lifetime. These are “real” cancers histologically, but their detection leads to treatment (surgery, radiation, endocrine therapy) that provides no benefit. Estimates of overdiagnosis rates in mammography screening vary widely — from 5% to 40% depending on methodology. Most experts place the figure at around 15–25% of screen-detected cancers.
These harms are real and should be part of an informed decision about screening participation. Most women who understand both the benefits and the harms still choose to participate in routine screening.
What Happens After an Abnormal Result
- Recall notice — you receive a letter inviting you for additional assessment; this is not a diagnosis
- Additional imaging — extra mammogram views, spot-compression views, or ultrasound
- Most cases resolve here — the majority of recalls result in a Category 1 or 2 assessment after additional imaging
- BI-RADS 4 or 5 → biopsy — if a finding remains suspicious, a needle biopsy (core biopsy or fine needle aspiration) is arranged to obtain cells or tissue for pathology
- Result discussion — results are discussed with a radiologist, breast physician, or surgeon; if cancer is confirmed, referral to a multidisciplinary breast cancer team follows
Being recalled does not mean you have cancer. Most recalled women do not. However, prompt follow-up of any recall is important.
High-Risk Surveillance
Women at significantly elevated risk of breast cancer — including those with a known BRCA1 or BRCA2 pathogenic variant, a strong family history, or prior chest irradiation — need a different approach:
- Earlier start (typically from age 30–40, or 10 years before the youngest first-degree relative was diagnosed)
- Annual rather than biennial screening
- Breast MRI — higher sensitivity than mammography, particularly in BRCA carriers; recommended alongside mammography in high-risk women
- Genetic counselling — to clarify risk level and appropriate surveillance
Referral to a familial cancer clinic or high-risk breast clinic is appropriate for women with a strong family history.
Further Reading
- BreastScreen Australia — Program Information — Australian national screening programme
- Cancer Australia — Breast Cancer Screening — national guidance
- NHS — Breast Screening (Mammogram) — UK programme information
- American Cancer Society — Mammogram Guidelines — US perspective and decision aids
Related Guides
- Breast Cancer: Understanding the Diagnosis and Treatment Options
- Skin Cancer Prevention and Screening
- Cervical Cancer: Causes, Screening, Prevention, and Treatment
- Genetic Testing: What It Can and Can’t Tell You
- Preventive Health — Screening and Health Maintenance
Last updated: May 2026