The relative effect of mammographic screening on breast cancer mortality by socioeconomic status

Effects of socioeconomic status on cancer patient survival: counterfactual event-based mediation analysis

PURPOSE

This study investigated the direct and indirect effects of socioeconomic status (SES) on the survival time of cancer patients by using cancer stage to create a pathway from SES to health outcomes and facilitate a mechanistic inference.

METHODS

Both a traditional mediation analysis and a counterfactual event-based mediation analysis were applied to SEER (The Surveillance, Epidemiology, and End Results) data from the National Cancer Institute of the United States. A Cox proportional hazards model for survival analysis was performed in the mediation analysis.

RESULTS

The counterfactual event-based mediation analysis showed that the effect of SES on survival time was partially mediated by stage at diagnosis in lung (12%), liver (14.33%), and colorectal (9%) cancers. Investigation of the fundamental mechanism involved thus established the direct effect of SES on survival time and the indirect effect of SES on survival time through stage at diagnosis. Moreover, the mediation analysis also revealed that the disparity in timely diagnosis (i.e., stage at diagnosis) caused by SES was slightly significant.

CONCLUSIONS

SES can either affect cancer survival directly or indirectly through stage at diagnosis. Opportunities to reduce cancer disparity exist in the design of early detection policies or mechanisms for patients with varying resources.

Impact of chronic diseases on effect of breast cancer screening

Background

Although breast cancer screening reduces breast cancer mortality at the population level, subgroups of women may benefit differently. We investigated the impact of health status on the effect of breast cancer screening.

Methods

The study included 181 299 women invited in two population‐based screening programs in Denmark and 1 526 446 control subjects, followed from April 1981 to December 2014. Poisson regressions were used to compare the observed breast cancer mortality rate in women invited to screening with the expected rate in the absence of screening among women with and without chronic diseases. Chronic diseases were defined as any diagnosis in the Charlson Comorbidity Index during 4 years before the first invitation to screening.

Results

Almost 10% of women had chronic diseases before first invitation to screening. Whereas we observed a reduction in breast cancer mortality following invitation to screening of 28% (95% CI, 20% to 35%) among women without chronic diseases, only a 7% (95% CI, −39% to 37%) reduction was seen for women with chronic diseases (P‐value for interaction = .22). For participants, the reduction, corrected for selection bias, was 35% (95% CI 16% to 49%) for women without, and 4% (95% CI −146% to 62%) for women with chronic diseases (P‐value for interaction = .43).

Conclusion

Our data indicate a marginal effect of mammography screening on breast cancer mortality in women with chronic diseases. If our results are confirmed in other populations, the presence of chronic diseases will be an important factor to take into consideration in personalized screening.

[Influence of Sociodemographic Factors on Type of and Stage at Diagnosis in Breast Cancer]

This study examines the influence of sociodemographic factors on the type of and stage at diagnosis in breast cancer in Germany.

METHOD

As part of the certification of the breast cancer centers by the German Cancer Society (DGK), the Institute of Medical Sociology, Health Services and Rehabilitation Science (IMVR) conducted nationwide post-stationary postal patient surveys (n=852). The influence of sociodemographic factors on the type of diagnosis and on the stage at diagnosis were each analyzed using a multinomial logistic regression.

RESULTS

45.5% palpated the tumor by themselves, 33.4% were diagnosed by mammography screening and 16.6% by gynecological check-up. Being diagnosed by screening was associated with an early stage cancer. Furthermore, breast cancer patients without private health insurance or with a low educational level were less likely to be diagnosed by a gynecological check-up. Patients within screening age (50-69) had higher odds for an early stage breast cancer. Patients with a low educational level had lower odds for an early stage breast cancer.

CONCLUSION

Fifty percent of the breast cancer patients were not diagnosed by screening. Mammography screening appears to be more sensitive in detecting early stage cancer, since we found an association between diagnosis by screening and an early stage cancer. Age outside of the screening range and a low educational level might be risk factors for an advanced stage breast cancer. High screening rates, especially for these risk groups, seem to be important for early detection of breast cancer.