This page provides an overview of the various methods used to screen for breast cancers.
As of June 2018, more than 80% of female breast cancers were diagnosed at stages I and II. Less than 5% were diagnosed at stage IV (Canadian Cancer Statistics, 2018). The Canadian Cancer Society attributes this to early detection through organized breast cancer screening programs.
We also have links to the breast cancer screening programs in each province.
Mammography is one of the most important tools for detecting breast cancer and premalignant lesions (abnormal regions in the breast that might become cancer). Most women who were diagnosed with breast cancer only because of a mammogram are asymptomatic, meaning the patient did not have any signs or symptoms of breast cancer, and would not have known about their cancer otherwise.
Digital mammography was developed to improve the accuracy of screening for women with denser breast tissue that may obscure the image quality of traditional mammograms. It is often performed with computer-aided diagnoses, known as a double reading. Digital mammography has also been very successful in finding half the cancers missed by film mammography for women who are still in their 40s. It is also safer in that it only contains ¾ of the radiation required for imaging purposes compare to that of traditional film. In some trials, digital mammography has reduced mortality rates by 4.4 per cent, although this comes with an increase in over-diagnosed cases by 21 per cent. Its long-term risks and benefits have yet to be assessed.
Mammograms during pregnancy are generally regarded as safe. The amount of radiation is small, and a lead shield over the abdomen is used to shield the fetus from the radiation. That said, many pregnant women choose to postpone their mammogram until after their pregnancy is finished, so that they do not have to worry about any potential harm to the fetus. Radiation can certainly cause harm to a fetus, but it’s not clear unclear whether mammograms in particular are a risk, because the amount of radiation that the fetus receives is so small. If you are pregnant and you need a diagnostic mammogram, talk to your doctor about what diagnostic method is best for you. An ultrasound of the breast is often used as a safe alternative to a mammogram for pregnant women.
Benefits and risks
The benefits of screening include better prognosis as well as less intensive treatment when diagnosed at an earlier stage. Research suggests that mammography can reduce breast cancer mortality rates by 20%–35% in women over the age of 50. When treated at an earlier stage, fewer lymph nodes are also removed, which are unto themselves an important part of the immune system and an indicator of cancer staging. The benefits of earlier treatment also serve to reduce overall costs to the health system.
No form of medical screening, however, is perfect. The process of screening may cause emotional stress and anxiety in the patient undergoing screening because it can sometimes lead to false positives and unnecessary biopsies. There is also some physical discomfort associated with the compressing force of a mammogram machine. The stress and discomfort you will endure during a mammography outweighs the emotional stress and physical pain you could endure if you are diagnosed with cancer.
The Canadian Task Force on Preventative Health Care (CTFPHC) ruled that Canadian women under 50 who are at “average risk” of developing breast cancer should not have a mammogram for these specific reasons. They have also pushed to extend the interval between mammograms from two to three years for women between 50-69 years of age – no randomized trial was performed to support this ruling. This is a greater reduction than its United States of America counterpart. In addition, they have advised against any use of Breast Self-Examination (BSE) and recommend a complete termination of training of BSE. The report does exempt anyone with a genetic predisposition to developing breast cancer from its recommendations.
The American and Canadian Cancer Societies as well as the Canadian Breast Cancer Foundation explicitly disagree with the CTFPHC’s findings on the grounds that the task force utilized evidence from outdated trials and did not include oncologists and specialists familiar with screening in their independent third party analysis of information that was calculated primarily from computer modelling. All three organizations actively promote screening from the age of forty.
It is important to understand that if a patient is asked to return for a second mammogram, it automatically qualifies as a ‘False Positive’, which means the result suggests cancer even though no cancer is actually present and the second set of imaging reveals nothing. After an initial screening, 10-15 per cent may get a callback, yet only one per cent will require a needle biopsy. The exaggerated numbers give the appearance that the test causes more harm than good, and while a request to return may be emotionally stressful, overcoming this is more beneficial than delaying screening and having to overcome the emotional and physical stress from an aggressive cancer and intensive treatment. False negatives are also a reality, which call into question the recommendations by the CTFPHC to extend the interval in between screening.
Women should talk with their doctor about the benefits and risks of mammography, when to start screening, and how often to be screened.
- More about mammography (Canadian Cancer Society)
- Traditional versus digital mammography (National Breast Cancer Foundation)
- Video: Mammography visit (BC Cancer Screening)
- Video: Mammogram for breast cancer — What to expect (Mayo Clinic)
Magnetic resonance imaging (MRI)
Where Magnetic resonance imaging (MRI) is appropriate, it should be used in addition to mammography rather than in its place, since the combination of the two screening modalities gives a higher sensitivity than either of them would alone. An MRI is an imaging test that uses powerful magnetic forces and radio-frequency (RF) waves to make detailed 3-dimensional pictures of organs, soft tissues, bone and most other internal body structures.
Ultrasounds are also now being utilized in conjunction with mammograms. This technique is beneficial in that it can distinguish solid lumps from less harmful benign liquid cysts, as well as measuring how much blood is flowing to a specific area of the breast. An ultrasound is an imaging test that uses high-frequency sound waves to produce images of structures in the body. An ultrasound works by bouncing sound waves off solid parts of the body. It is also considered a substitute for women who cannot undergo a mammogram due to pregnancy. As with all methods, it does contain several drawbacks, including the inability to detect calcium deposits, an early warning sign for cancer.
Clinical breast exams
A clinical breast exam (CBE) is a physical examination of the breast done by a health professional who is trained to find abnormalities and warning signs of breast cancer. This in-office medical exam will either be done by your family doctor or gynecologist at your annual exam. Clinical breast exams are used to find a lump or change in the breast that may mean a serious problem is present. CBE is also used to check for other breast problems such as mastitis or a fibroadenoma. Talk to your doctor about how often you should receive a clinical breast examination. There are no risks in having a clinical breast examination.
There is greater consensus in the field that a breast self-exam (BSE) should be relegated to an important yet secondary role in the detection of breast cancer. The importance of the BSE practice stems from its ability to find “interval” breast cancers (false prognosis within a 12 month period after a mammogram) among women undergoing regular mammographic screening. Tumour growth can escalate at an increasingly rapid pace between screenings. Routine breast self-examination is commonly recommended by familial cancer clinics for women at hereditary risk.
There is substantial variation across studies evaluating the effectiveness of breast self-examination as a means of screening. Much of this is due to variance in compliance and poor self-response from trial participants. Additional trials did not take into account socio-economic differences in the participants, and how that would impact their proficiency in performing BSE. Several trials attempted to stratify participants by geographic clusters while neglecting the importance of matching the personal and physical attributes of the subjects.
The Canadian Task Force on Preventative Health Care (CTFPHC) is ironically an outspoken advocate against BSE, reporting in 2000 that it only results in increased invasive diagnostic procedures. The Task Force also claimed that the concerns over breast deformity and scar tissue outweigh any perceived benefits. In addition, the United States National Cancer Coalition and the United States National Cancer Institute claimed there is no scientific evidence that BSE saves lives or enables women to detect breast cancer earlier. The Canadian Cancer Society actively promotes BSE, and both its American counterpart as well as the Canadian Breast Cancer Foundation endorses it as a preventative measure, albeit not explicitly. The Federal government supports screening in accordance with the World Health Organization’s guidelines on cancer.
The disagreement about the effectiveness of BSE does not mean that you should not educate yourself about this practice. Proper examination techniques are essential to performing a correct BSE. Proper education allows women to understand what feels “normal” in order to recognize when something feels different. Often, a clinical BSE by a healthcare professional is the best method for educating woman in developing a proper baseline by which to examine themselves. However, because many leading health organizations no longer promote BSE, it is reasonable to assume that fewer women are being taught it and thus conducting it less routinely. Furthermore, over-reporting can sometimes decrease the perceived benefits of performing BSE. Breast awareness through self-examination is encouraged for women in their twenties, and strongly recommended for those with a family history of breast cancer. Anyone diagnosed with a genetic predisposition is encouraged to maintain a low threshold for reporting concerns to their general practitioner.
All women should be “breast aware” and report any changes or discomfort in the breasts to their physician or healthcare provider. Rapid diagnosis can improve survival rates and lessen the intensiveness of the physical and emotional stress associated with a patient’s level of treatment. Most importantly, it saves lives.
Breast cancer screening with implants
If you have breast implants or are considering getting breast implants, it is very important to understand that breast implants make routine mammography screening more difficult (via Health Canada), but breast implants do not prevent women from being screened for breast cancer. Screening and detection is more difficult because the implants often interfere with screening mammograms. Saline-filled implants, or cohesive silicone gel implants can be placed under the chest muscle to interfere less with mammograms (via csaps.ca).
A woman with breast implants will often require additional images in order to detect abnormal changes (via screeningforlife.ca). Breast implants may require special views for the detection of cancer, and breast compression (hard pressure) during screening is associated with a very small risk of implant rupture or deflation (via Toronto Cosmetic Surgery Institute).
The risk of breast cancer does not differ in women with breast implants, detection is just more difficult. Mammograms are an important tool for detection – women already at risk of breast cancer need to consider these factors before receiving breast implants (via csaps.ca). Women who have breast augmentation with implants require routine screening mammography to evaluate any remaining breast tissue (via breast-cancer.ca).
Breast cancer screening for pregnant women
(taken from breast-cancer.ca)
Although breast cancer is the most common cancer diagnosed during pregnancy, it is rare. About one out of every 3000 pregnant women is diagnosed with breast cancer (via Canadian Cancer Society). When women are pregnant or breastfeeding, their breasts are often tender, swollen and have many small lumps. It is important for women to be very familiar with their breasts to notice any changes before, during and after pregnancy. It is recommended for women to routinely have a clinical breast exam during this times period when your breasts are irregular.
Breast imaging of a pregnant woman with a palpable breast abnormality begins with an ultrasound – mammography is performed if the ultrasound findings are suspicious for malignancy. Screening mammography is not routinely performed when a woman is pregnant. This makes it harder to find breast cancer early, so breast cancer is often found at a later stage in pregnant women. Mammography that is done in pregnancy is for diagnostic purposes, to evaluate suspected cancer, check the contralateral breast and to assess clinical findings that are not clarified by ultrasound.
The breast undergoes physiological changes during pregnancy and lactation. Because of this, breast disorders encountered in pregnancy are often benign and secondary to hormonal changes. The possible effect of mammographic radiation on the fetus means that mammography should be avoided during pregnancy. The developing fetus is most susceptible to effects from radiation in the first few weeks of gestation. In general, radiation doses of more than 5 rads (radiation absorbed dose) or 50 mGy (milligray) are considered harmful. A four view standard mammogram with abdominal shielding exposes the fetus to 0.4 rads or 4 mGy.