Relative Survival With Early-Stage Breast Cancer in Screened and Unscreened Populations

Abstract

Relative survival and disease-specific survival are two statistics that measure net survival from a cancer diagnosis, excluding other causes of death. In most cases, these two rates are comparable. However, in some cancer types for which cancer screening is performed, relative survival is often greater than disease-specific survival. This divergence has been attributed to mechanisms such as the "healthy user effect" and overdiagnosis of indolent tumors detected by screening. Using relative survival rate as a marker of these mechanisms, we examined the association of breast cancer screening with relative survival rates for women diagnosed with early-stage breast cancer. In population-based data from the National Cancer Institute's Surveillance, Epidemiology and End Results registry, we examined relative survival rates in women diagnosed with stage I breast cancer or ductal carcinoma in situ who were in highly screened vs less-highly screened groups, based on time period, age group, and insurance status. In this analysis, relative survival rates for early-stage breast cancer were higher than disease-specific survival, even exceeding 100% in populations experiencing higher rates of screening (ie, women diagnosed during the era of widespread uptake of mammography, age older than 40 years, and women with health insurance coverage). The favorable outcomes observed in screen-detected breast cancers are at least in part attributable to the healthy user effect and overdiagnosis of indolent tumors. Therefore, survival rates may not accurately reflect the effectiveness of cancer screening. These findings have implications for counseling of patients and future clinical studies of active monitoring approaches in breast cancer.

Figure 1.. Trends in 10-year relative survival (1980–2006) for women with ductal carcinoma in situ and stage I breast cancer, compared to rates of screening mammography, stratified by age.

A) Rates of mammographic screening among United States women 40 and older. Data obtained from published reports from CDC National Center for Health Statistics B) Relative survival rates for women aged 40 and older with ductal carcinoma in situ or stage I breast cancer has been over 100% since the late 1980s, when screening became widespread. American Joint Committee on Cancer 6^th edition stages are used (system in use at the time). Data are from the National Cancer Institute’s Surveillance, Epidemiology and End Results 9 Research Data set, April 2020 release, based on data form the November 2019 submission (SeerStat version 8.3.6).

Figure 2.. Relative and disease-specific survival for women with stage I breast cancer, stratified by age and health insurance status.

A) Women 40 and older with stage I breast cancer had 10-year relative survival of greater than 100% when compared with age- and race-matched counterparts without cancer, and tracked higher than their disease-specific survival B) In women younger than 40 with stage I breast cancer, 10-year relative survival was less than 100%, and tracked closely with disease-specific survival. C) Women age ≥40 with stage I breast cancer and private or Medicare-based insurance had a relative survival of greater than 100% when compared with age- and race-matched counterparts without cancer D) In women aged ≥40 with no insurance or Medicare-only insurance, relative survival was less than 100%, and tracked more closely with disease-specific survival. American Joint Committee on Cancer 6^th edition stages are used (system in use at the time). Data are from the National Cancer Institute’s Surveillance, Epidemiology and End Results 9 Research Data set, April 2020 release, based on data form the November 2019 submission (SeerStat version 8.3.6), using years 2004–2016 for A-B, and 2007–2016 for C-D (years insurance data was available).

Figure 3.. Relative and disease-specific survival for women with ductal carcinoma in situ (DCIS), stratified by age and health insurance status.

A) Women 40 and older with DCIS had 10-year relative survival of greater than 100% when compared with age- and race-matched counterparts without cancer, and tracked much higher than their disease-specific survival. B) In women younger than 40 with DCIS, 10-year relative survival was less than 100%, and tracked closely with disease-specific survival. C) Women age ≥40 with DCIS and private or Medicare-based insurance had a relative survival of greater than 100% when compared with age- and race-matched counterparts without cancer D) In women aged ≥40 with no insurance or Medicare-only insurance, relative survival was less than 100%, and tracked closely with disease-specific survival. American Joint Committee on Cancer 6^th edition stages are used (system in use at the time). Data are from the National Cancer Institute’s Surveillance, Epidemiology and End Results 9 Research Data set, April 2020 release, based on data form the November 2019 submission (SeerStat version 8.3.6), using years 2004–2016 for A-B, and 2007–2016 for C-D (years insurance data was available).