Incidence stands for absolute number of all newly diagnosed cases of a particular disease that develop in a defined population in one calendar year.

The incidence consider the number of cases of disease not the number of patients. If an individual develops different types of cancer in the same year, they are counted in the incidence statistics for each of those cancers. However, the following are not included in cancer incidence:

• a new occurrence of cancer of the same histological type in the same organ (e.g. multiple lesions in the colon);
• new primary cancers of paired organs at the same site (e.g. the left and right breasts) if the histological type of both cancers is the same;
• recurrences of cancer, even if they occur several years after the diagnosis of the primary cancer;
• metastases of the same primary cancer, even if they occur in another organ.

Regarding incidence, the SLORA portal provides three types of measures: incidence (total number of cases), crude incidence rate, and age-standardised incidence rate.

The SLORA portal also provides estimates of the number of new cancer cases for the current calendar year, calculated using the Dyba and Hakulinen method and based on analyses of past trends. The modelling uses data on cancer site, period of diagnosis, and age at diagnosis for the last ten years, for which data collection and processing have been completed. The incidence estimate is updated once a year, at the time of preparation of the annual report.

In the SLORA portal, data by geographic units classify patients according to their permanent residence at the time of diagnosis or death, into administrative units as defined in the 2000 Regulation on the Standard Classification of Territorial Units (SKTE). The SKTE-3 level (12 statistical regions) and the SKTE-4 level (58 administrative units) are used. Administrative units are classified one-to-one into statistical regions; that is, differing boundaries are not taken into account when individual municipalities within the same administrative unit are officially classified into two different statistical regions.

Geographic units are always defined according to the official definitions at the time of diagnosis of cancer, and it is the user’s responsibility to ensure, when preparing data by geographic unit, that the output is appropriate for the time period during which changes to geographic units occurred. At the level of statistical regions, a change occurred in 2005 when, due to changes in the boundaries of the settlements of Marija Reka and Knezdol – and consequently in the municipal boundaries (Prebold and Trbovlje)—the boundary between two statistical regions (Savinjsko and Zasavsko) was altered; and in 2015, when the municipality of Litija was transferred from the Central Slovenia to the Zasavsko statistical region. In the Pesnica and Ruše administrative units, patients have been classified separately only since 1990; before that year, all patients were grouped under the Maribor administrative unit. In the reports, all three administrative units are always shown as a single entity with a value equal to the average of these three units.

In smaller areas, such as municipalities, or settlements, the number of cancer cases can be very small, which can lead to unreliable results and a risk of identifying individuals. Therefore, we present data at a level that allows reliable and secure interpretation – administrative units and statistical regions. A specific epidemiological study is required to conduct a detailed analysis of cancer incidence in smaller geographic areas.

Mortality stands for absolute number of all deaths from a particular disease in a defined population in one calendar year.

Mortality data are collected, processed and published by the National Institute of Public Health (NIJZ) in accordance with the international guidelines of the World Health Organization (WHO). The SLORA portal contains data on individuals who have died of cancer since 1985. Minor deviations (no more than a few cases per year) between the official mortality figures and the data displayed on the SLORA web portal occur for three reasons:

• For some residents of the Republic of Slovenia who died abroad, the Death Certificate is received only after data processing at the National Institute of Public Health (NIJZ) has been completed; therefore, these deaths are included in the official mortality statistics for the year in which this data was received, while the SLORA portal displays all deaths in the year in which they actually occurred.
• For deaths occurring between 1985 and 1996, causes of death in the official mortality statistics are classified according to the 9th revision of the ICD (International Classification of Diseases), and for later periods according to the 10th revision of the ICD. The SLORA portal uses the 10th revision of the ICD for all years. For the period 1985–1996, the Slovenian Cancer Registry prepared a conversion between the 9th and 10th revisions of the ICD, which may result in minor deviations between official NIJZ reporting and the data displayed on the SLORA portal.
• Official mortality reports include all persons who meet the official definition of the population of the Republic of Slovenia that was in effect during a given period. The SLORA portal includes in its displays all individuals who had permanent residence in the Republic of Slovenia at the time of death, regardless of the official definition of the population.

Three types of mortality measures are available on the SLORA portal: mortality (number of cases), crude mortality rate and age-standardised mortality rate.

The choice of a standard population for age standardisation using the direct method depends on the purpose of the analysis. The SLORA portal provides users with the following standard populations, which are frequently used in cancer epidemiology:

• the World Standard Population (1961 and 2001 versions) – most commonly used in international comparisons involving countries from around the world;
• the European Standard Population (1976 and 2013 versions) – most commonly used in international comparisons involving countries within Europe;
• the Slovenian standard population (based on the 2002 census) – most suitable for comparisons within Slovenia.

The population structure for each standard is shown in the table below:

Prevalence refers to the number of all patients with a specific disease who are alive on a specific date. In the SLORA web portal, prevalence is reported for the last day of the selected calendar year. If a person has been diagnosed with multiple different cancers, each individual cancer is counted in the prevalence, except when calculating the prevalence of all cancer sites combined, in which case each person is counted only once. For this reason, the sum of the prevalences for individual sites is always greater than the prevalence of all cancers combined. Depending on when individuals were diagnosed, we distinguish between total and partial prevalence.

The source of prevalence data is the Slovenian Cancer Registry database, which contains information on patients diagnosed with cancer from 1950 onward who were permanent residents of the Republic of Slovenia at the time of diagnosis. On the SLORA portal, we present prevalence data from 1985 onward, as estimates for earlier years are not sufficiently reliable.

Lifetime prevalence refers to the number of all cancer patients who are alive on a selected date, regardless of when they were diagnosed. If a person has been diagnosed with multiple different cancers during their lifetime, each individual cancer is counted, except when calculating the prevalence of all cancer sites combined, in which case each person is counted only once.

Partial prevalence refers to the number of all cancer patients who were alive on a selected date and were diagnosed with cancer during a precisely defined period before the calculation date. One-year partial prevalence includes patients who were diagnosed within one year before the calculation date; patients included in the 1–4-year prevalence were diagnosed between one and up to five years before the calculation, and so on. If patients were diagnosed with multiple different cancers during the selected period, they are counted in the prevalence for each individual cancer, except when reporting the partial prevalence for all sites combined, in which case each person is counted only once.

For cancer, data on partial prevalence are particularly important, as they reflect the number of patients at different stages of the course of disease. For example, 1-year prevalence mostly includes patients at the time of initial treatment; 1–4-year prevalence mostly includes patients during regular follow-up clinical examinations; and 5–9-year prevalence – and especially 10+-year prevalence – includes patients who have completed treatment and are mostly enrolled in long-term follow-up. Important: The stages of disease progression are only an approximation and do not reflect an individual’s course of treatment.

Survival estimates the proportion of patients who are still alive after a specified period following diagnosis. The survival of cancer patients is typically reported for one, three, five and ten years after diagnosis. Survival calculated in this way is called observed survival.

In clinical studies, where the primary interest is deaths resulting from a specific disease, all deaths from other causes are treated as censored in the analysis (so-called cause-specific survival). Such an approach would also be appropriate in population-based studies of cancer registry data; however, in practice, the number of patients included in these studies is generally too large to verify the exact cause of death for each individual, and the official causes of death collected in Slovenia by the National Institute of Public Health (NIJZ) are often insufficiently precise for such analyses. For this reason, and because observed survival rates are not comparable across different populations, relative or net survival is now used in population-based studies instead of observed survival. Causes of death are not needed to calculate relative or net survival; nevertheless, the method is designed so that the result is a good approximation of patient survival, as if only the cancer under study were considered as the cause of death.

The SLORA portal does not currently enable the display of survival rates, but this feature is planned for future updates. Survival analyses are available in the annual reports of the Slovenian Cancer Registry and in selected scientific publications. An international comparison of survival rates for Slovenian patients are published in the European Cancer Information System (ECIS) and in analyses from the EUROCARE and CONCORD projects.