Cancer remains the leading cause of death and a pathology where health inequalities are particularly marked. These inequalities stand at all stages of the medical history of the disease, and are revealed with indicators as incidence, survival and mortality. Regarding detectable cancers as breast cancer, screening appears as a key step in the construction of inequalities.(1) In most European union member states, breast cancer screening is organised with a mammography screening. However, there are still differences in the way screening programmes are implemented.(2) In France, breast cancer is the first women cancer in incidence and mortality with 58968 new cases estimated for 2017 and 11883 death for the same year.(3) Public health policy has organized screening in the general population for this cancer, according to European recommendations and implying a high quality assurance. The organized breast cancer screening (OBCS) has been conducted, nationwide since 2004. A screening mammography is offered every two years to women aged 50 to 74 at average risk for this cancer. They receive from management structures in charge of this screening (SMS), an invitation to visit an accredited radiologist’s office. A radiological imaging of the breast with two views plus a clinical breast examination is realized. Two different radiologists assure readings. In the last three year, the national participation rate remains stable around 48% [Santé Publique France], which is lower than the European recommendation set at 70% in view of the expected mortality reduction target.(4) However, it persists a so-called individual screening, apart from age and time recommendations, and that would be achieved by about 15% of women.
A large literature report studies on determinants of non-adhesion to the OBCS, in a great number of countries with different organization and screening modalities and concerning diverse populations (low income, ethnic group, rural areas).(5, 6) Consensually established determinants are usually grouped in five categories. (a) Socio-demographics characteristics as age, marital status, low income; (b) environmental characteristic as living in rural areas (7); (c) health system utilization: having a general practitioner; (d) health behaviour as doing other screening, alcohol or tobacco consumption; (e) psychological factors as beliefs and concern. Most of these factors are socially determined, and considerable social inequalities in participation in OBCS are reported. In France, participation rates vary considerably across geographical areas, with some departments having a participation rate close to the European benchmark while others have a very low rate (< 25%). At a finer level (infra-communal) there are also large differences in participation. In particular studies, using ecological indices of deprivation (8), highlight social and territorial inequalities: women living in disadvantaged area or far from a radiologist’s office less participate.(9–12)
The World Health Organization (WHO) define the social determinants as the main causes of inequalities in health. These are the circumstances in which people are born, grow, live, work and age, and the systems set up to deal with the disease. These determinants are multiple, stand to individual from global policy and act in complex interactions. Determinants of non-adhesion to the OBCS can also be considered according to the social ecological model which incorporate all social and ecological factors that can affect breast screening participation.(13) In summary, individual factors refer to demographic, socio-economic determinants and health behaviours. Interpersonal factors concern social support and network. Community factors refer to cultural norms and community organization. Health system factors concern health insurance, distance to health facility and finally structural factors are relative to wealth inequalities and place of residence. These determinants when modifiable can be the target of intervention to increase OBCS participation and reduce inequalities in participation.
Different strategies can be implemented to increase participation to breast cancer screening, especially in populations with low-income or in rural areas, who have less access to screening. Among these strategies, mobile mammography units are currently operating in many countries: USA (14), Brazil (15), and at least 7 in European Union (16). MMUs can be include in the national program of organized cancer screening (Sweden (17), or in regional program (10, 14, 18), in addition to a national screening program. The literature underlines that MMU can increase access for under-screened groups by increasing physical and economic access to screening while reducing barriers for women (structural barriers and out-of-pocket costs). However, very few studies allow a high evidence-based evaluation by randomised controlled trial. Moreover, regardless of their target, while the social and territorial inequalities in participation in screening are proven, the majority of evaluated interventions have not taken the existence of these inequalities into account in their design and have not set out to reduce social and territorial inequalities in participation as an objective with the risk to increase it.(19) Nevertheless, it is now well established, when implementing public health interventions aimed at reducing socio-territorial inequalities, that we have to consider some consensual recognized principles: the existence of a social gradient across the whole society, the relevance and the value of the principle of proportionate universalism (20), the multilevel, intersectoral, multidisciplinary nature of the intervention.(21)
In France, a MMU is used for 30 years in a rural area of 279755 inhabitants in 2019, without any prospective trial protocol. Its retrospective evaluation suggests that, when used in remote areas, it could reduce social and territorial inequalities, in particular inequalities due to the distance to an approved radiology centre.(10) However, the potential value of this MMU depends on many local characteristics such as socio-demographic, geographical and medical characteristics. Therefore, in the French context, there is very little evidence on how to intervene to reduce health socio-territorial inequalities in screening, so public health decision-makers are unable to base proposals on evidence. Only an experiment rigorously conducted and evaluated over a large territory and considering contextual determinants would make it possible to establish the true effectiveness of the MMU according to the environment in which it is used and to establish the optimal conditions of its efficiency throughout France.
We present here a randomised controlled trial of a population health intervention research conducted as a collaborative project to reducing or even eliminating territorial inequalities in participation to the OBCS in France remote areas. With a complement objective to identify the most efficient modalities to incorporating a mobile mammography unit in the organization of breast cancer screening.