Abstract
Objective To examine participation in screening mammography among women aged 40 to 74 and identify which factors are associated with those women who participate in screening.
Design Secondary analysis of the cross-sectional 2012 Canadian Community Health Survey.
Setting Canada.
Participants A population-based national sample of 18 312 women aged 40 to 74.
Main outcome measures Women’s participation in screening mammography in the 2 years preceding the 2012 Canadian Community Health Survey; women’s preventive health activities (ie, having a regular doctor, a recent physical checkup, and a Papanicolaou test), which were adjusted for sociodemographic factors.
Results Participation in recent screening mammography was highest among women aged 60 to 69 (70.3%), followed by those aged 50 to 59 (63.4%) and those aged 70 to 74 (58.4%). Almost one-third (31.4%) of women aged 40 to 49 had had a screening mammogram in the past 2 years. Having a regular doctor (odds ratio [OR] = 3.30, 95% CI 2.90 to 3.73), a physical checkup in the past year (OR = 3.06, 95% CI 2.30 to 4.08), or a Pap test in the past 3 years (OR = 3.47, 95% CI 3.18 to 3.79) more than tripled the odds that women had had a recent screening mammogram.
Conclusion Aside from age being a factor associated with women’s participation in screening mammography, factors related to women’s health care use (having a regular doctor, a recent physical checkup, and a recent Pap test) demonstrated a stronger association with women aged 40 to 74 having had recent mammograms. The association between women’s participation in screening and their preventive health activities implies that the doctor’s office is an appropriate venue for conversations regarding the potential benefits and harms of screening mammography.
It is estimated that in 2016 breast cancer was the cause of death for 4900 Canadian women and was diagnosed in 25 700 women—representing more than a quarter (25.8%) of new cancer cases in women.1 Women aged 50 to 69 are estimated to have accounted for a little more than half of new cases (51.0%).1 Modifiable factors associated with breast cancer include alcohol consumption, smoking, hormone replacement therapy, and postmenopausal obesity.2–4 Biologic factors associated with increased risk of breast cancer include older age, having a first-degree relative with breast cancer, reproductive factors, genetic predisposition, and clinically diagnosed denser breast tissue.3–5
Screening mammography represents a secondary preventive strategy against breast cancer death and is indicated for asymptomatic women within a certain age range, often between the ages of 50 and 69.6 Its aim is to reduce breast cancer mortality.6 However, screening mammography can also lead to false-positive results, overdiagnosis, overtreatment, and psychological distress.7 The overall mortality benefits of screening mammography among women aged 40 to 59 were called into question by findings from the Canadian National Breast Screening Study. After 25 years of follow-up, women aged 40 to 59 who received an annual mammogram experienced no reduction in breast cancer mortality compared with those who underwent physical examination alone.8 However, after evaluating data from 20 cohort and 20 case-control studies, the International Agency for Research on Cancer concluded that for women aged 50 to 69, the benefits of screening mammography outweighed the harms, and that for women aged 40 to 49 the evidence was too limited to draw conclusions.9
In the literature, a 25% to 30% reduction in breast cancer mortality is often attributed to biannual screening mammography among women aged 50 to 69.10 Some authors contend that the literature on screening mammography exaggerates its benefits and minimizes the associated harms such as false-negative results, overdiagnosis, and overtreatment.7,10,11 Two international studies found that women vastly overestimated mammography’s ability to reduce breast cancer mortality.12,13 A lack of knowledge of the harms associated with screening mammography might unduly influence women in favour of mammography.7,10,11
An analysis of Canadian Community Health Survey (CCHS) data showed that levels of mammography use among women aged 50 to 69 increased from 40% in 1990 to 72% in 2001—mammography use remained stable until 2008.14 Subsequent to 2008, the Canadian Task Force on Preventive Health Care (CTFPHC) revised its guidelines on screening mammography. The age for routine screening was extended from 69 to 74 years; the time interval between screening for women aged 50 to 69 was extended from 2 years to 2 to 3 years; and it was recommended that women aged 40 to 49 not be routinely screened (previous guidelines did not address this age group).15 The CTFPHC reported an unfavourable benefit-harm profile for women aged 40 to 49; this finding underscores the importance of quantifying this age group’s participation. Canadian literature reporting on factors influencing mammography participation has typically focused on women aged 50 to 69.14,16–19 However, the CTFPHC’s revised guidelines point to the need to expand on the collection of information on participation levels to include women aged 40 to 49 and 70 to 74.
A search of the published literature to date yielded no study reporting Canadian mammography participation and factors that influence women’s participation based on population-based data collected after 2008. This study focuses on screening mammography, and thus differs from many of the previous analyses of the CCHS data, which did not differentiate between screening and diagnostic mammography.14,16–18 Using data from the 2012 CCHS, this study examined participation in screening mammography among women aged 40 to 74 and identified the factors that are associated with those women who participate in screening.
METHODS
Data source
This study used survey data from Statistics Canada’s (a Canadian federal department) cross-sectional 2012 CCHS microdata file. The survey data are collected via telephone interviews. As the microdata file is for public use and contains anonymized data, ethics approval was not necessary. The CCHS includes Canadian residents 12 years of age and older from all provinces and territories, excluding people residing in institutions, full-time members of the Canadian Forces, and those living on First Nations reserves, in the Region of Nunavik, and in des Terres-Cries-de-la-Baie-James.20 For calculations based on the survey data to be representative of the Canadian population, Statistics Canada assigns each CCHS respondent a weight that corresponds to the number of individuals in the Canadian population that she or he represents.21 The study sample consisted of 18 312 women aged 40 to 74, weighted to represent 7.6 million women aged 40 to 74 in the Canadian population (Figure 1).21
Variables
The CCHS asked women aged 35 or older the following questions: “Have you ever had a mammogram, that is, a breast x-ray?” (yes or no); and “When was the last time?” (< 6 months, 6 months to < 1 year, 1 to < 2 years, 2 to < 5 years, and ≥ 5 years ago). Women whose responses were recorded as “don’t know,” “refused,” or “not stated” to the questions asking if they ever had a mammogram and when the last time was were excluded from the analysis of mammography participation. Women were also asked, “Why did you have it?” As multiple responses were accepted, a respondent could have legitimately reported reasons suggesting that she had received both screening and diagnostic mammograms. For example, a woman who had undergone screening mammograms over several years and then had undergone a diagnostic mammogram to investigate a lump might have responded “screening” and “follow-up of a breast problem.” However, for the purposes of this study, women who responded that their screening reasons included “part of regular checkup or routine screening,” “age,” “family history of breast cancer,” or “using hormone replacement therapy” and who indicated that they had had a mammogram less than 2 years ago were considered to have participated in screening mammography and are herein referred to as screening participants. Women who reported that the only screening reason was “previously detected lump” or “follow-up of breast cancer treatment” or “breast problem” were considered to have participated in diagnostic mammography. Finally, women whose only response to “Why did you have it?” was “other” were excluded from the analysis.
The CCHS participants were asked to provide their height and weight, from which we calculated their body mass index. Other variables were selected based on their association with breast cancer and their inclusion in similar studies; they included the following: age, marital status, number of years since immigration, household income, education attainment, having a regular doctor, number of years since last physical checkup and last Papanicolaou test, frequency of alcohol consumption, smoking status, and province or territory.2,4,14,16–19
Frequencies, bivariate tabulations, and logistic regressions were performed to examine associations between independent variables and being a screening mammography participant in the 2 years before the 2012 CCHS interview using SPSS software, version 22.22 Odds ratios (ORs) and their associated 95% CIs were calculated, and then the model was adjusted for age, marital status, and household income.
RESULTS
In the weighted sample of women, most were Canadian born, were married or in common-law relationships, had household incomes of $60 000 or greater, and had graduated from a postsecondary institution (Table 1). Most women were non-smokers (81.2%), had a regular doctor (92.0%), and had had a physical checkup in the past 2 years (70.7%).
Most women who had had a mammogram reported having done so within the past 2 years (60.6%) (Table 2). Of the women who reported a screening mammogram in the past 2 years, 15.9% also cited a diagnostic reason for having that mammogram (data not shown). Most screening participants reported 1 screening reason (88.8%), and 9.8% reported 2 screening reasons (data not shown). The percentage of women who cited at least 1 diagnostic reason for screening was substantially lower than the percentage of women who cited at least 1 screening reason (10.8% compared with 69.1%, respectively). By age group, 31.4% of women aged 40 to 49, 63.4% of women aged 50 to 59, 70.3% of women aged 60 to 69, and 58.4% of women aged 70 to 74 were screening participants. Table 3 shows that within the 40-to-49 age group there was a 37.2% point difference between the province with the highest screening participation rate (Prince Edward Island) and the province with the lowest rate (Quebec). Regional variation was lowest within the 50-to-59 age group.
Aside from age, the factors most strongly associated with being a screening participant were having a regular doctor (OR = 3.30, 95% CI 2.90 to 3.73), having had a physical checkup in the past year (OR = 3.06, 95% CI 2.30 to 4.08), and having had a Pap test in the past 3 years (OR = 3.47, 95% CI 3.18 to 3.79) (Table 4).
DISCUSSION
For more than a decade, mammography participation rates among Canadian women aged 50 to 69 have remained stable; 72.7% of women in 2001, 72.5% in 2008,14 and 72.2% in 2012 reported having had a mammogram in the past 2 years. The finding that screening was most likely among women aged 50 to 69 was not surprising, as this is the age group most commonly targeted by health care providers and screening programs and is the group most likely to benefit from screening mammography. Participation in screening mammography in the 2 years preceding interviews was highest among women aged 60 to 69. Women are encouraged to begin screening mammography at age 50, but it might take time to establish a routine or women might not have their first screening until their mid or late 50s.
As more than half of women aged 70 to 74 (58.4%) participated in screening mammography just 1 year after the CTFPHC extended its recommendation to routinely screen women up to the age of 75, one can conclude that most women did not cease screening mammograms at age 69.15 In 2011, the CTFPHC contraindicated screening mammography for women aged 40 to 49 on the basis that its potential harmful effects outweigh its potential benefits15; however, 31.4% of women in this age group participated in screening. The discrepancies that emerged in provincial or territorial screening participation levels for women aged 40 to 49 and 70 to 74 probably relate to differences in the age of eligibility and public messaging. Although national guidelines are provided by the CTFPHC, health care is the responsibility of the provinces or territories, and differences among jurisdictions in medical practices, recommendations, and policies for screening mammography might influence screening mammography participation.
Although sociodemographic factors were associated with screening participation (ie, being married and having higher household income), factors related to health care use exerted a stronger effect. Having a regular doctor, a physical checkup in the past year, and a Pap test in the past 3 years were strongly related to whether women aged 40 to 74 participated in screening mammography in 2012. The associations with having a regular doctor and a physical checkup in the past year are consistent with the finding that women aged 50 to 69 who did not have a regular doctor and had not seen that doctor in the past year were far more likely to have not had a recent mammogram; however, the associations observed here were stronger than those found in previous studies.14,19 Specifically, Poole et al19 found that having had a checkup in the past year doubled the odds of having had a screening mammogram in the past 2 years, whereas we found that it tripled the odds.
Having a regular doctor, a recent physical checkup, and a recent Pap test are clearly related. This implies that conversations related to breast screening are initiated in doctors’ offices and that doctors’ offices are an appropriate venue for dialogue between the health practitioner and the patient on the benefits and harms of screening mammography. Smoking is a risk factor for breast cancer,2 yet consistent with findings from the 2006 and 2008 CCHS,14,19 daily smokers were less likely to be screening participants. A more targeted approach to initiating discussion on screening mammography among smokers might be a consideration for doctors.
Limitations
Several limitations are inherent in the data set and in the application of this research. The data precluded a clear distinction on whether the last mammogram was for screening or diagnostic reasons. As the responses are not corroborated against clinical records, social desirability bias might be present, where women report their mammograms as having taken place more recently than they actually did. The CCHS responses are self-reported and are therefore subject to recall bias. Examining participation levels in light of whether women were at higher risk of developing breast cancer would have allowed one to look at differential patterns of screening across average- and high-risk individuals, but the CCHS does not include such questions. Also, women’s perceptions of their risks of developing breast cancer and views of the potential benefits and harms of screening mammography are not solicited in the CCHS but might influence mammography uptake.
Conclusion
Aside from age being a factor associated with women’s participation in screening mammography, factors related to health care use, namely, having a regular doctor, demonstrated a stronger association with women aged 40 to 74 having had recent mammograms than any sociodemographic or lifestyle-related factors. The jurisdiction-specific information found in this study should be of value to governments and advocacy and patient groups in assessing the effectiveness of their screening programs. Future research should consider corroborating mammography histories with clinical records, examining mammography participation in light of individual risk factors, and capturing information on women’s perceptions of screening mammography. The CTFPHC’s update of its 2011 guidelines is expected to be released some time this year, and given the 25-year follow-up results of the Canadian National Breast Screening Study, guidelines around screening mammography could change. The findings of this study provide baseline participation levels against which future participation can be compared.
Acknowledgments
We are grateful to Kathryn Wilkins for her advice and editorial assistance.
Notes
EDITOR’S KEY POINTS
The aim of screening mammography is to reduce breast cancer mortality by detecting breast cancer in its early stages. This study examined participation in screening mammography among women aged 40 to 74 and identified the factors associated with participation.
Although sociodemographic factors were associated with screening participation (ie, being married and having higher household income), factors related to health care use exerted a stronger effect. Having a regular doctor, a physical checkup in the past year, and a Papanicolaou test in the past 3 years were strongly related to whether women aged 40 to 74 participated in screening mammography.
Discrepancies that emerged in screening participation levels across Canadian regions in the 40-to-49 and 70-to-74 age groups might be related to provincial and territorial differences in recommendations and policies regarding mammography screening.
POINTS DE REPÈRE DU RÉDACTEUR
Le but de la mammographie de dépistage est de réduire la mortalité causée par le cancer du sein grâce à un diagnostic précoce. Cette étude voulait connaître le degré de participation à cet examen chez les femmes de 40 à 74 ans et déterminer les facteurs associés à ce taux de participation.
Même si plusieurs facteurs sociodémographiques influençaient le taux de participation au dépistage (p. ex. le fait d’être mariée et d’avoir un revenu familial plus élevé), les facteurs liés à la santé avaient encore plus d’influence. Ainsi, le fait d’avoir un médecin régulier, d’avoir eu un bilan de santé au cours de l’année précédente et d’avoir eu un test de Papanicolaou au cours des 3 années précédentes étaient des facteurs très importants pour inciter les femmes de 40 à 74 ans à participer au dépistage.
Les taux de participation différents observés dans les diverses régions du Canada chez les groupes d’âge de 40 à 49 ans et de 70 à 74 ans pourraient être dus à des différences entre les provinces et territoires dans les politiques et les recommandations relatives à la mammographie de dépistage.
Footnotes
This article has been peer reviewed.
Cet article a fait l’objet d’une révision par des pairs.
Contributors
Ms Volesky developed the study, performed the analysis, and wrote the manuscript. Dr Villeneuve provided feedback on each step of the study and reviewed the manuscript.
Competing interests
None declared
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