1. Screening basics — who, when, how often

Current US guidance (USPSTF 2024)

• Start at 40 for average-risk women
• Every 2 years through age 74
• Individualize for 75+
• Higher risk? Start earlier, screen more often — discuss with your clinician

Source: USPSTF recommendation | PubMed

Current Canada guidance (CPAC 2023–2024)

• Average risk: screening every 2–3 years, ages 50–74
• Ages 40–49: "informed decision-making" (benefits + harms discussion)
• Dense breasts (BI-RADS C/D): some provinces offer annual mammogram or supplemental ultrasound

Source: CPAC breast screening summary

Who is "higher risk"?

• Strong family history (especially first-degree relatives with breast/ovarian cancer before 50)
• Known genetic mutations (BRCA1/2, PALB2, TP53, etc.)
• Personal history of breast cancer, DCIS, or high-risk lesions
• Prior chest radiation (e.g., for Hodgkin lymphoma) before age 30
• Dense breasts (BI-RADS C/D) — see below

2. Dense breasts — what they are, why they matter

What is breast density?

Breast density describes how much fibroglandular tissue (dense, white on mammogram) vs fatty tissue (dark on mammogram) you have. It's reported as BI-RADS categories:

• A: Almost entirely fatty
• B: Scattered fibroglandular densities
• C: Heterogeneously dense (may obscure small masses)
• D: Extremely dense (lowers mammogram sensitivity)

About 40–50% of screening-age women have dense breasts (C or D).

Why it matters

1. Masking effect: Dense tissue is white on mammogram — and so is cancer. Small cancers can be hidden.
2. Independent risk factor: Dense tissue itself increases breast cancer risk, separate from the masking issue.

What to do if you have dense breasts

• Why ultrasound? Finds additional cancers mammogram misses. A 2025 Canadian study (Gordon et al.) showed supplemental ultrasound detects ~3 extra cancers per 1,000 screens in dense breasts. PubMed
• Coverage/access: Varies by region. Ontario: annual mammogram recall for BI-RADS D. BC: supplemental ultrasound covered for C/D in some cases. Ontario Health | BC ultrasound policy (PDF)

US density notification rule (FDA 2023)

All US facilities must now inform patients if they have dense breasts and discuss supplemental screening options. FDA rule

10-second script for your doctor

3. Prevention levers — what you can control

Genetics load the gun, but lifestyle often pulls (or doesn't pull) the trigger.

Strong evidence

• Exercise: Regular physical activity (150+ min/week moderate aerobic + strength training) reduces risk. NCI Prevention PDQ
• Limit alcohol: Even moderate drinking (1 drink/day) increases risk. Less is better. NCI Alcohol & cancer
• Maintain healthy weight: Obesity (especially postmenopausal) raises risk. CDC Obesity & cancer
• Breastfeeding: If you have kids, breastfeeding reduces risk — duration matters.

Moderate evidence / other factors

• Avoid smoking: Linked to higher breast cancer risk and worse outcomes.
• Minimize unnecessary hormone exposure: Fewer years of menstruation (late menarche, early menopause, pregnancy/breastfeeding) = lower lifetime risk.
• Sleep & metabolic health: Insulin resistance, chronic inflammation, poor sleep — all may contribute to risk.

What doesn't work or is unproven

• Avoiding deodorant/antiperspirant: No evidence of increased risk.
• Avoiding underwire bras: No evidence of increased risk.
• Vitamin supplements: No clear prevention benefit from routine multivitamins or antioxidants in well-nourished people.

4. Menopausal hormone therapy (MHT) and breast cancer risk

This is where fear meets fuzzy math. Let's use real numbers.

What WHI (Women's Health Initiative) actually showed

• Estrogen + Progestin (E+P): Increased breast cancer risk by ~0.08% per year (8 extra cases per 10,000 women per year)
• Over ~5 years in WHI: absolute increase of ~0.4% (about 4 extra cases per 1,000 women over 5 years)
• Estrogen-only (E-only): No increase, possibly slight decrease (for women without a uterus)

Source: WHI estrogen+progestin report (PMC)

Context for decision-making

MHT is the most effective treatment for moderate-to-severe hot flashes and GSM (genitourinary syndrome of menopause). The absolute risk increase is small, especially in the first few years. For many women, benefits outweigh risks when used for the shortest effective duration at the lowest effective dose.

Practical approach

• If considering MHT: Discuss your personal risk profile (family history, dense breasts, other factors) with your clinician.
• Route matters: Transdermal (patch/gel) may have a different risk profile than oral for some outcomes.
• Duration: Use for shortest time needed; re-evaluate periodically.
• Screening: Keep up with mammograms as recommended.

NAMS 2022 position statement: PubMed

5. Do-this-week master checklist

• ☐ Book/confirm your mammogram is scheduled — don't skip cycles.
• ☐ Pull your report and note BI-RADS density.
• ☐ If C/D, request supplemental ultrasound.
• ☐ If D, ask about annual recall where you live.
• ☐ Lock in prevention levers: exercise, less alcohol, weight/metabolic health.
• ☐ If considering MHT: use absolute risk numbers (0.08%/year; ~0.4% over ~5 years for WHI E+P) and get individualized counseling.