Mammography Screening Guidelines in Ontario
In Ontario, women at average risk should undergo mammography screening every 2-3 years between ages 50-74, following the Canadian guidelines which differ substantially from American recommendations. 1
Age-Specific Screening Recommendations for Ontario
Women Ages 50-74 Years
- Mammography every 2-3 years is the standard recommendation for average-risk women in this age group in Canada, including Ontario. 1
- This recommendation is based on evidence demonstrating mortality reduction in this age group. 1
- Clinical breast examination is recommended in addition to mammography. 1
Women Ages 40-49 Years
- Canadian guidelines do not routinely recommend screening mammography for women in their 40s unless they have higher-than-average risk factors. 1
- This contrasts sharply with American organizations like the American Cancer Society, which recommends annual screening starting at age 40. 2, 3
- The decision not to screen routinely in this age group is based on concerns about breast tissue density in premenopausal women, which decreases mammography sensitivity. 4
Women Ages 75 and Older
- Women aged 75 and older can continue screening but are not actively recruited into organized screening programs. 5
- Screening should be considered if life expectancy exceeds 10 years. 5
Key Differences Between Canadian and American Guidelines
The Ontario/Canadian approach is notably more conservative than American recommendations:
- Starting age: Canadian guidelines recommend age 50, while American organizations recommend age 40-45. 1, 2
- Screening interval: Canadian guidelines recommend every 2-3 years, while most American organizations recommend annual screening. 1, 3
- Rationale: The Canadian approach weighs the harms of screening (false-positives, overdiagnosis, anxiety) more heavily against benefits in younger women. 1, 4
Higher-Risk Women Requiring Earlier/More Frequent Screening
Women with the following risk factors should begin screening earlier and more frequently than average-risk women:
- Significant family history of breast cancer. 1
- BRCA1 or BRCA2 genetic mutations. 1, 6
- Personal history of breast cancer. 6
- History of chest radiation at young ages. 6
- Calculated lifetime risk of 20% or more. 6
For these women, screening may begin as early as age 25-30 and should include supplemental MRI in addition to mammography. 6
Important Quality Considerations
Follow-up timing is critical for abnormal results:
- Quality guidelines recommend a delay of 60 days or less between screening and diagnosis for abnormal results. 1, 5
- Delays longer than 180 days are associated with larger tumors and lymph node metastases. 1, 5
Common Pitfalls to Avoid
- Do not apply American screening guidelines directly to Ontario patients – the provincial screening program follows Canadian recommendations, which are more conservative. 1
- Do not dismiss screening in women over 74 if they are healthy with good life expectancy – individualized decisions are appropriate. 5
- Do not fail to identify higher-risk women who require earlier and more intensive screening than the standard Ontario guidelines. 1, 6