Understanding Breast Screening: Mammograms, Ultrasound, and the Role of Breast Density

Breast cancer screening is a vital part of proactive health management for women. Early detection can significantly improve the chances of successful treatment and long-term outcomes.

While mammograms are the primary screening tool, ultrasound can be an invaluable resource, particularly for women with dense breast tissue or when an abnormality is found on a mammogram.

In this article, we’ll explore the differences between these two technologies, when each should be used, how breast density impacts screening decisions, and provide an overview of breast screening guidelines across Canada.

The Basics of Mammograms and Ultrasound

1. Mammograms

• What It Is: Mammography is the most widely used screening tool for breast cancer. It involves low-dose X-ray technology to create images of the breast tissue. During the procedure, the breast is compressed between two plates to spread out the tissue for clearer imaging.1

• How It Works: Mammograms can identify changes or abnormalities, such as masses, calcifications, and distortions in breast tissue, which may indicate the presence of cancer even before a lump can be felt.

• Benefits: Mammograms are particularly effective for women over 50. They can detect tumors that are too small to be felt, allowing for earlier intervention and increasing the likelihood of successful treatment (American Cancer Society).

• Limitations: Mammograms are less effective in women with dense breast tissue. Dense tissue appears white on a mammogram, similar to cancerous tissue, making it difficult to distinguish between the two. In such cases, additional imaging like an ultrasound may be necessary.

2. Breast Ultrasound

• What It Is: Ultrasound uses high-frequency sound waves to create detailed images of breast tissue. Unlike mammography, it does not involve radiation. A handheld device called a transducer is moved over the skin of the breast to capture images.2

• How It Works: Ultrasound is especially useful for differentiating between solid masses (which could be cancerous) and fluid-filled cysts (which are usually benign). It provides a more detailed view of specific areas that may not be as clear on a mammogram.

• Benefits: Ultrasound is safe for women of all ages, particularly those with dense breast tissue. It is also valuable for providing a closer examination of any suspicious areas detected by a mammogram.

• Limitations: Ultrasound is not typically used as a primary screening tool because it may miss some signs of cancer that mammograms can detect, such as microcalcifications. However, it serves as an excellent complementary tool when additional imaging is required.

Breast Density: What It Is and Why It Matters

Breast density refers to the proportion of fibrous and glandular tissue compared to fatty tissue in the breasts. Approximately 40-50% of women aged 40 to 74 have dense breasts, which can affect the accuracy of mammogram readings.3

What Are Fibrous and Glandular Tissues?

• Fibrous Tissue: This tissue consists of collagen, providing structure and shape to the breasts. Think of it like a supportive network that holds everything in place, similar to how scaffolding supports a building.

• Glandular Tissue: This includes the milk-producing system, made up of lobules (milk-producing glands) and ducts (tubes that carry milk to the nipple).

Together, fibrous and glandular tissues appear dense on a mammogram, making it harder to detect abnormalities, as both dense tissues and potential cancerous growths show up as white areas in the image.

Breast Density Categories

Your breast density is classified into four categories, which radiologists use to help assess the level of density seen on a mammogram:

1. A - Almost entirely fatty: Breasts contain mostly fatty tissue, making it easier to detect abnormalities on a mammogram.
2. B - Scattered areas of fibroglandular density: There are some areas of dense tissue, but most of the breast is fatty.
3. C - Heterogeneously dense: There are many areas of dense tissue, which can obscure small masses on a mammogram.
4. D - Extremely dense: The breast is mostly dense tissue, making it very challenging to identify abnormalities with mammography alone.

Knowing your breast density is essential because women with heterogeneously dense or extremely dense breasts (Categories C and D) may need supplementary imaging, such as ultrasound or MRI, to ensure accurate screening.

How to Determine Your Breast Density

• Mammogram: The most common way to determine breast density is through a mammogram. The radiologist assesses the proportion of dense tissue in the breast and categorizes it into one of the four levels mentioned above.

• Other Imaging Methods: In some cases, breast MRI or ultrasound can provide additional information about breast density. These methods are typically used when further imaging is needed rather than for the primary assessment of breast density.

Breast Density Information in Canada

In Canada, each province has different practices regarding breast density reporting following a mammogram:

• British Columbia, Alberta, Saskatchewan, Ontario, Nova Scotia, Prince Edward Island, Newfoundland & Labrador: These provinces include breast density information in the mammogram results sent to women and their healthcare providers.

• Quebec: The decision to inform a patient about their breast density is typically left to the healthcare provider or radiologist. While some clinics provide this information voluntarily, it is not yet standardized.

• The Territories (Yukon, Northwest Territories, Nunavut): Practices can vary in the territories. Women should check with their local healthcare facilities to understand how breast density information is communicated.

If you’re uncertain about how to access your breast density information, we encourage you to contact our team of clinicians, who can guide you through the process.

When to Use Ultrasound for Breast Density and Abnormalities

1. Dense Breast Tissue

• Why Ultrasound Helps: In women with dense breasts (Categories C and D), ultrasound can provide clearer images, highlighting areas that might be obscured on a mammogram. It is particularly effective at distinguishing between solid masses and fluid-filled cysts.

• When It’s Used: If a woman is known to have dense breast tissue, her healthcare provider may recommend an ultrasound in addition to regular mammograms. This combined approach increases the chances of early detection.

2. Abnormalities Detected on a Mammogram

• Follow-Up Imaging: If a mammogram reveals an abnormality, such as a mass or an area of concern, ultrasound is often the next step. It allows for a more detailed view, helping to determine the nature of the suspicious area (e.g., solid or cystic). In some cases, it may guide further procedures like needle biopsies to sample the tissue.

• Targeted Examination: Ultrasound focuses on specific areas of concern, providing real-time imaging that assists healthcare providers in diagnosis and management planning.

Breast Screening Guidelines Across Canada

Screening guidelines vary across provinces and territories. Here’s a general overview:

Ontario

• Starting Age: As of fall 2024, women aged 40 and older can self-refer for mammograms, improving early detection efforts.
• Screening Frequency: Every 2 to 3 years for women aged 50 to 74. Women aged 40 to 49 can choose more frequent screening, particularly if they have risk factors.

British Columbia

• Starting Age: Women aged 40 to 74 are eligible for screening. For those aged 40 to 49, screening every 2 years is available, especially if they have a family history of breast cancer.
• Screening Frequency: Every 2 years for women aged 50 to 74.

Alberta

• Starting Age: Women aged 45 to 74 are recommended to start regular screening. Those aged 40 to 44 can choose to be screened, especially if they have risk factors.
• Screening Frequency: Every 2 years for women aged 50 to 74.

Saskatchewan

• Starting Age: Women aged 50 to 74 are automatically invited for screening. Women aged 40 to 49 should consult with their healthcare provider to discuss their risk factors and determine if screening is appropriate.
• Screening Frequency: Every 2 years for women aged 50 to 74.

Manitoba

• Starting Age: Women aged 50 to 74 are routinely invited for screening. Women aged 40 to 49 can be referred by a healthcare provider, especially if they have risk factors.
• Screening Frequency: Every 2 years for women aged 50 to 74.

Quebec

• Starting Age: The Quebec Breast Cancer Screening Program (PQDCS) invites women aged 50 to 69 for screening. Women outside this age group should discuss their risk factors with their healthcare provider.
• Screening Frequency: Every 2 years for women aged 50 to 69.

Atlantic Provinces (New Brunswick, Nova Scotia, Prince Edward Island, Newfoundland & Labrador)

• Starting Age: Most Atlantic provinces encourage women aged 50 and older to undergo screening. Some provinces, like Nova Scotia and Prince Edward Island, offer screening for women aged 40 and older, especially if they have risk factors.
• Screening Frequency: Generally, every 2 years for women aged 50 to 74.

The Territories (Yukon, Northwest Territories, Nunavut)

• Starting Age: Women aged 50 to 74 are typically eligible for routine screening. Women outside this age range should consult their healthcare provider to discuss their individual screening needs.
• Screening Frequency: Every 2 years for women aged 50 to 74.

Advocacy for Expanding Screening to Age 40

The Canadian Cancer Society (CCS) is urging provinces and territories to lower the starting age for breast screening programs to 40 for individuals at an average risk of developing breast cancer. This change reflects evolving evidence and the calls for action from patients, as many women aged 40 to 49 are currently being excluded from screening.4 The CCS emphasizes the importance of regular mammograms in finding breast cancer early and improving treatment success rates.

CCS also advocates for self-referral options for individuals at high risk of breast cancer, regardless of age, to address gaps in provincial program access. If you have concerns about your breast health or need help navigating your screening options, our team is here to guide you.

The average risk of developing breast cancer, highlighted by the CCS, include:

• Age: risk increases as women get older, with most cases of breast cancer being diagnosed in women aged 50 and older.

• Family History: a medical history of breast cancer in a close relative, such as a mother, sister, daughter, grandmother, aunt, or even niece.

• Genetic Mutations: mutations in genes like BRCA1 and BRCA2 can increase the risk of developing breast cancer.

• Reproductive Factors: early onset of menstruation or late menopause increases the length of exposure to estrogen over time, increasing the average risk.

• Lifestyle Factors: a sedentary lifestyle, excessive alcohol consumption, and obesity after menopause.

The Takeaway

Mammograms are the primary tool for breast cancer screening, especially for women aged 50 and older.

However, women with dense breasts or abnormalities found on a mammogram may benefit from supplementary imaging like ultrasound. Understanding the differences between these technologies and when each is appropriate is an important step in managing your breast health. Awareness of provincial screening guidelines and discussing a personalized screening plan with your healthcare provider is key.

If you need assistance in finding information about your breast density or screening options, we encourage you to contact our team. We’re here to support you through every step of your breast health journey.

Sources:

1. National Institute of Biomedical Imaging and Bioengineering

2. Dan Q, Zheng T, Liu L, Sun D, and Chen Y Ultrasound for Breast Cancer Screening in Resource-Limited Settings: Current Practice and Future Directions. PubMed Central 2023:; Mar 31. 

3. Center for Disease Control and Prevention - About Dense Breasts 

4. Canadian Cancer Society Media Release: Time for change: Breast screening programs must start at age 40