The main findings in this study were lower breast cancer incidence in Crete than in Sweden and at the same time a developing trend of higher mortality rates in the Cretan population than in the Swedish population. In Sweden, a decrease in breast cancer mortality was evident during the last decade. However, on Crete, both incidence and mortality of breast cancer were rising during this time. This is a striking difference in the pattern of disease burden for populations of these two regions of the European continent. Regarding survival rates, trends of survival in Sweden has increased over time in contrast to a declining trend on Crete. Interestingly, initial data for the studied time-period showed an inverse relationship of both 5-year and 10-year survival, with higher survival rate on Crete. A breaking point in survival rate appeared around the year of 2000.
Breast cancer mortality and survival are tightly related. One of the most important, modifiable, known parameters with influence on the prognosis is early detection, by way of facilitating early treatment. Several factors are involved in the process leading to diagnosis, from the individuals own detection and insight at the debut of symptoms, to the availability and utilization of health care. Mammographic screening on a population level is an established method to approach early detection of breastcancer before clinical symptoms occur (24). In Sweden, 60% of all breast cancer cases are detected through the national screening program for women between 40 and 74 years of age (20, 25).
In countries with a tradition of mammography screening of breast cancer, an increase in incidence rates and a decrease in mortality rates have been evident for decades (26). This may point to an increased incidence related to improved diagnostics. Nevertheless, potential overdiagnostics may complicate the interpretation of epidemiological health statistics. In a metaanalysis from 2012, the overdiagnostics was estimated to be 11% during lifetime for a woman invited to the screening program, and 19% during the specific time-period of inclusion in the screening program (27). However, in many countries, the incidence rise began before the mammography screening programs were implemented, also seen in countries who introduced screening programs relatively late (26). In different populational settings, different challenges are distinguished related to features of the population (28). The mammography screening of women, at least for the age-group 50–69 years, is a way to significantly reduce mortality rates of breast cancer (24).
Early detection is the prerequisite for early, effective treatment with medical drugs and interventions that is already known to work (18). Another way into early detection and early start of treatment is to make the diagnostical process more effective. In Sweden, a time-regulated, standardized health care process is used for symptoms leading to a high suspicion of several cancers including breast cancer. Through this process, from the referral of the patient to a specialized oncological hospital unit, the individual has priority to the different examinations required, and the time space between examinations and clinical consultations are strictly time-regulated (19).
It is important to keep in mind that individual cases from mortality data may have gained their diagnosis several years earlier, making the data of incidence and mortality or survival, respectively, hard to compare in the same year. Nevertheless, clinical endpoints measured as survival show this inverse relationship early in the studied time-period, namely a higher survival rate on Crete with the breaking point appearing around the year of 2000.
These findings must be seen against a multifactorial background where both risk factors and salutogenic factors play important roles. The structure of the health care systems and the availability of health care differ between the studied regions. A discrepancy in health literacy may also be evident especially for perceptions of health and disease among the populations studied. Also, dietary factors, where the Mediterranean diet has been particularly studied, might be relevant (14).
Another point of view in general is certainly the cultural aspects that must be implemented when proposing an intervention of the health care system, especially regarding interventions that are voluntary such as a mammography screening. This is of particular concern in areas associated with high personal integrity, such as clinical investigations of the female breast. Both regarding patient-compliance, cultural aspects of the clinical consultation and differences of the health care architecture, it is equally important to locally adapt each structural intervention. Also, communicative factors such as language barriers and variations in definitions accompany all epidemiological studies (29).
The strength of the study is that both the Swedish and Cretan data are solid and reliable. In Sweden, there is a historical tradition of registries with one of the world’s oldest cancer registries, started in 1958, with a national coverage (20). The reporting of all new cancer cases is obligatory by law in Sweden, both from physician in charge as well as the responsible unit for pathological and cytological laboratory. In this way, the Swedish Cancer registry cover approximately around 99% of all cases and in 2015 an investigation showed that 100% of the reported cases were verified with cytology or histology, pointing to a valid and accurate measure (23). The Cancer Registry of Crete has reached high numbers of data quality by following the European Network of Cancer Registries (ENCR) quality standards, which evaluate for dimensions (i.e. completeness, reliability, timeliness and continuity).
A limitation in this study is that the Greek data is only available from a specific region of the country, the island of Crete. This constitute a potential confounding factor if attempted to generalize the data at a country level. The Swedish screening tool per se, might introduce some bias. According to Swedish National Quality Registry of Breast Cancer (NKBC), every tumor of the breast found through screening is treated even if the knowledge is scarce about how the tumor would have developed with time if left untreated (26). This perception may have influence on the incidence as well as the mortality data, possibly contributing to higher number of cases found, and consequently lower mortality rate in Sweden.
The changing landscape of breast cancer incidence and mortality in diverse regions of the European continent call for the recognition of local, population features to optimize selected efforts with respect of socio-cultural differences. It would be interesting to stratify the breast cancer cases constituting the data for the incidence and mortality, respectively, to analyze if there are early (in situ) or late (invasive, metastasized) stages overrepresented in any data material. The introduction of a population-based screening program is dependent on voluntarily participation of the women called. Therefore, it is warranted to further shed light on possible sociocultural obstacles to support women’s participation in screening programs.
In conclusion, this study shows epidemiological discrepancies of breast cancer incidence and mortality between the Swedish and the Cretan population. Although the incidence is slowly rising in both regions, the mortality is increasing on Crete in contrast to Sweden where the mortality trend is decreasing. The findings reveal a rising survival rate in Swedish breast cancer patients, while the survival trends on Crete are falling. The main difference between the two regions is that Sweden since decades has implemented a national breast cancer screening program, which has not been implemented in Greece. An interpretation of these findings is that differences in health care systems and health policies as well as sociocultural factors between the two countries maight play an important role for early diagnosis and treatment. This point in favor of the implementation of a national screening program and possibly a streamlined, standardized course of investigation to improve early diagnostical processes and early treatment.