Survival after breast cancer according to participation in organised or opportunistic screening and deprivation

1 Introduction

Breast cancer is the most common cancer worldwide with 47.8 new diagnosis per 100,000 women in 2020 [1] . In France, the standardized incidence of breast cancer was estimated at 99.9 per 100,000 women in 2018 [2] . Breast cancer among women is a cancer with good prognosis, with a 5-years net survival around 90 % in 2018 [3] . An increase in survival has been observed over the years, which can be explained by therapeutic progress but also by the implementation of screening practices, enabling the discovery of cancers at an earlier stage.

In 2004, the organised breast cancer screening program was generalized in France. It targets women aged 50–74, without high risk of breast cancer, to undergo mammogram and clinical examination every 2 years [4] . This organised screening (OrgS) is managed at the regional level by regional cancer screening coordination centers, which are responsible for sending invitations and managing the follow-up of participating women [5] . Despite European recommendations and targets set at 70 %, participation in this OrgS was 48.6 % in France in 2019 [6] .

In parallel to OrgS, there is also opportunistic screening (OppS), which consists of mammograms performed at the request of general practitioner, gynecologist or women. This screening is normally recommended for women at high risk of breast cancer. However, it is also performed in women who had no clinical indications or proven risk factors. The exact rate of participation in this screening is more difficult to estimate [7] . This problem of identifying and evaluating OppS is also apparent in many other European countries [8] .

Numerous studies have shown the importance of screening on survival after breast cancer. Indeed, it has been shown in different countries that women who participate in screening have a higher survival rate than women who are not screened 9101112131415 . However, socioeconomic inequalities also have a direct impact on survival after breast cancer, as well as on participation in screening 161718 . A review of the literature showed that the most deprived women were less likely to participate in breast cancer screening [19] . This impact of deprivation on participation to screening may then lead to decreased survival after cancer. Furthermore, some studies have shown that among screened women survival decreased with increasing levels of deprivation 202122232425 .

In a previous study, we showed that women whose cancer was diagnosed through OrgS had higher 5-year net survival than women whose cancer was not discovered by this screening. Women screened by OrgS had good survival, regardless of the level of deprivation. In contrast, survival rates in non-attenders decreased with increasing deprivation. Thus, the difference in net survival between the 2 groups was greater when the level of deprivation was high [26] . Nevertheless, in this study, some of women among non-attenders may have undergone OppS, leading to an overestimation of survival for women who did not attend OrgS. A hypothesis was that OppS was greater in the less deprived areas, which could potentially explain the lack of difference between the two groups in these areas.

It therefore seems important to identify OppS and to study separately organised, opportunistic screening and non-screening-detected cancer, to investigate survival after breast cancer.

In this context, the aim of this study was to estimate 1- and 5-years net survival among women with breast cancer, according to their screening practice, i.e. OrgS, OppS or no screening, and taking into account the level of deprivation.