Cancer is not a single disease but rather a few hundreds of different diseases that can develop in any tissue or organ of the human body. As with any disease, it is important for a doctor to classify it according to an agreed system once a definitive diagnosis has been made, since the treatment approach and prognosis depend on the disease’s basic characteristics. The key characteristics relevant to cancer include the anatomical location of the tumour (cancer site), the type of tissue from which it originates (morphology), and the extent of the disease (stage) at the time of diagnosis. In addition to standard classifications, specific and supplementary classifications are used for certain cancers, as the characteristics they include are important for treatment, prognosis, or both.

Internationally accepted classifications, used in all countries and enabling better international comparisons of the burden of cancer, are primarily intended for statistical data analysis and, consequently, for comparability across studies and countries. The most widely established classifications categorise cancers by anatomical site (location), by tissue type (histological type), and by the extent of the disease at diagnosis (stage). For mortality and prevalence measures, the SLORA portal provides data only by cancer site.

On the SLORA portal, cancers can be classified by site and stage. Specific data preparation rules apply to non-melanoma skin cancer and sex-specific cancers.

To classify cancers by their site of origin, both in Slovenia and internationally, we use the International Statistical Classification of Diseases and Related Health Problems, developed by the World Health Organization. Numerous new findings are published in new editions of this classification. Since 1997, the Slovenian Cancer Registry has used the 10th revision; before that, it used the 8th revision and subsequently converted the data to the 10th revision.

The SLORA portal allows the display of cancer indicators in the “basic list” using a condensed list of cancer sites (list of cancer groups), and in the “detailed list” of cancers using an expanded list of sites. Please note that the list of cancer sites in the detailed classification also includes certain diseases from the group of neoplasms in situ and neoplasms of uncertain or unknown behaviour (from Chapter D of the ICD-10), which the Slovenian Cancer Registry also reports regularly. These are not included in the total number of all cancer cases (incidence) classified under Chapter C of the International Classification of Diseases (ICD-10).

List of cancer groups using basic classification  List of cancer groups using detailed classification

The SLORA web portal offers two display options:

• all cancer sites (C00–C96);
• all cancer sites excl. non-melanoma skin (C00-C96, excl. C44)

Reporting separately on all cancers excluding non-melanoma skin cancers, enabling direct international comparison of indicators. Non-melanoma skin cancers are common, usually non-fatal, and mostly treated in outpatient facilities, often in private institutions with incomplete reporting of cases, and are therefore excluded from many countries’ cancer statistics.

The presentation of sex-specific cancers is limited: if a particular cancer occurs in only one sex, the age-standardised rate calculated for both sexes combined is not shown.

At the time of diagnosis, the disease may be confined to the organ where it originates, or the cancer may already have invaded neighbouring tissues, spread to lymph nodes, or metastasised to distant organs. The SLORA web portal uses a simplified staging system that categorises the disease into one of three groups: localised disease, regionally advanced disease, and metastatic (or distant) disease, which is commonly used in cancer registries to define the disease stage. The simplified staging for solid tumours generally follows the TNM classification.

Haematological neoplasms (lymphomas and leukaemias) and poorly defined cancers are not classified according to the simplified staging system; therefore, the SLORA web portal displays the message: “For haematological neoplasms (C81–C96) and non-malignant (D), the stage is not determined.” The same applies to diseases in the group of neoplasms in situ and neoplasms of uncertain or unknown nature.