This study examined potential benefits and moderation effects of mammography screening on early breast cancer diagnosis and mortality among women aged 50-69 years at various health statuses. A generic CCI measure was used to identify women at different levels of overall chronic illness burden. Consistent with previous literature, our findings indicate that women at higher chronic illness levels were less likely to participate in mammography screening and to have breast cancer newly diagnosed at early stages, and were at greater risk of all-cause mortality.4,7−9 Our findings further provide empirical evidence that mammography may moderate the association between chronic illness burden and early breast cancer diagnosis and mortality.
Comorbidity may present barriers to breast cancer screening and complicate diagnostic decision-making.7,10 Similar to findings from a systematic review and meta-analysis study based on few high-quality studies in Europe or in the United States by Diaz et al. (2017) and a recently study conducted in Taiwan by Hsieh (2021),10,11 our study findings indicate that women aged 50-69 years at higher chronic illness levels were less likely to participate in mammography screening in Taiwan. As Fleming et al. (2005) indicated, comorbidity as a predictor of newly diagnosed breast cancer stage may relate to several hypotheses: the interaction between comorbid conditions and cancers at the cellular level may increase risks of metastasis, or comorbid conditions may constitute a competing demand against use of preventive services. Additionally, as observed in clinical settings, physicians are more likely to request mammography for women at higher general risk of breast cancer (e.g., family history), but less likely to request it for average-risk women with chronic illnesses.7 These all may exacerbate the odds of late-stage breast cancer diagnosis and prognosis among women with chronic illness.
Existing studies suggest that mammography screening and reducing barriers to health system access may decrease the risks of late-stage diagnosis and mortality among women with chronic illness. Most of these existing studies focus on older women and were conducted in Europe and the United States.7,12,15,18,33 To the best of our knowledge, no studies specifically examined potential benefits of mammography screening for stage at diagnosis or mortality among younger women at different health statuses in Asian countries. In general, our findings confirm the benefit of mammography screening, which increased the likelihood of early stage breast cancer diagnosis by 48% and decreased odds of all-cause mortality by 37%. Mammography screening significantly moderated the link between chronic illness burden and late-stage diagnosis and risk of all-cause mortality.
Our study has several strengths. It used four longitudinal nationwide population-based datasets linking NHI administrative claims, national cancer registry, death registry, and breast cancer screening registry in Taiwan. These included all women aged 50-69 years in 2010, or approximately 2.5 million population, and provided accurate screening attendance information for identifying screened and non-screened groups. In addition, the study database allowed us to generate a generic composite measure of total chronic illness burden from NHI administrative data, reducing potential recall bias from self-reported health status,10 or missing information due to using data from regional hospital-based electronic medical records.18 In addition, Czwikla et al. (2018) addressed methodology concern of selection bias issue as the results of mammography screening participants and nonparticipants are not comparable regarding various health statuses.33 To avoid potential selection bias as Czwikla et al. (2018) point out, we used an exact matching approach to generate balanced groups with different burdens of chronic conditions based on birth years and income status and compared outcomes of interest at the same chronic condition levels between screened and non-screened groups.
Nevertheless, this study also has several limitations. First, to compare results with existing studies,12,18we used the CCI to measure overall burden of chronic conditions. Future studies may use other types of comorbidity measures to investigate benefits of mammography among women at different health statuses. Second, some unobservable confounders are unavailable when investigating research questions using secondary administrative data, such as lifestyle factors and habits or breast cancer awareness. Finally, the data were from women aged 50-69 years in Taiwan. Results may not generalize to other health systems in other countries.
In conclusion, analyzing national population-based data in Taiwan, this study provides empirical evidence with respect to the moderation effect of mammography screening, which increased likelihood of early stage breast cancer diagnosis and decreased odds of all-cause mortality. Public health policy and strategies may be necessary to improve mammography participation and early detection efforts for women with comorbid conditions.