Organized Breast Cancer Screening Programs in Canada

1999 and 2000 Report

Diagnostic Investigations

When a lump or lesion is detected through CBE or mammography screening, additional assessment is normally required to establish or exclude the presence of cancer. The screening program notifies women with screen-detected abnormalities and their family physicians of the need for further assessment. For the most part, family physicians coordinate follow-up. Because mammography screening is offered to asymptomatic women and breast cancer is not present in the majority of women with screening abnormalities, the fear and anxiety associated with subsequent testing should be minimized by providing a timely, well-coordinated follow-up with only the appropriate number of interventions. For this reason, a number of programs have started to establish methods to streamline scheduling, track follow-up procedures and results, and provide additional support to women during the process. 

There is a growing trend towards using less invasive procedures before resorting to open surgical biopsy. Consequently the overall benign to malignant open biopsy ratio is well within the Canadian target of less than 2:1.

This process of further evaluating suspicious or uncertain findings following a breast screening examination is a normal part of the screening procedure. The success of screening programs in reducing breast cancer mortality in the population requires complete and timely follow-up in women with abnormal screens. In 1999 and 2000, complete follow-up information was available for over 90% of women with abnormal screening examinations. Among women screened, 10.4% were referred for additional assessment. For every 100 women with an abnormality found on screening, approximately six women subsequently received a diagnosis of cancer. 

Diagnostic investigations may include a clinical evaluation, radiologic work-up including diagnostic mammography with additional views (spot compression or magnification views), a comparison with previous mammograms and/or ultrasonography. Imaging procedures, including either a diagnostic mammogram and/or ultrasound, were performed for the majority of women aged 50 to 69 (88.2%) who underwent follow-up. For 72.4% of women of this age no further assessment was required. Figure 9 shows the proportions of women who received each diagnostic procedure after an abnormal screen. 

In order that a final diagnosis can be obtained, a small number of women may undergo a surgical consultation, fine-needle aspiration, core biopsy and/or surgical biopsy where appropriate¹⁵. There is a growing trend towards using the less invasive procedures before resorting to open surgical biopsy. Compared with 1997 and 1998 data, the number of fine-needle aspirations performed declined from 5.0% to 4.7% (Table 5). In 1999 and 2000, 90.7% of women aged 50 to 69 with a screen-detected abnormality did not require surgical biopsy to obtain a diagnosis. Of the women who did require a surgical biopsy, approximately 43 of every 100 were found to have cancer. This represents a benign to malignant open biopsy ratio of 1.3:1, which
is well within the Canadian target of # 2:1 (Table 2) and is also an improvement over the 1997 and 1998 open biopsy ratio of 1.6:1². Keeping the recall rate and the ratio of benign to malignant biopsies appropriately low is necessary to avoid inducing needless morbidity in healthy women. 

Table 5
Diagnostic procedures after an abnormal screen
in women aged 50-69, 1999 and 2000 screen years 

^a    All provinces combined.
^b    Range among provinces, reported as a percentage of women with abnormal findings. 

Note: Only first screens, with one year of follow-up, are included for Quebec data. 

Preventing breast cancer deaths through screening depends on detecting cancers early, before they are large enough to be felt or to have spread: in 1999 and 2000, 38.0% of invasive cancers detected were less than 10 mm in diameter and 75.7% had not spread to the lymph nodes.

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