Sources of cancer data and classification schemes used

Chapter on sources of cancer data and classification schemes used in the children, teenagers and young adults  UK cancer statistics report 2021

Cancer registration data were obtained from Public Health England’s National Cancer Registration and Analysis Service (NCRAS), the Northern Ireland Cancer Registry, the Scottish Cancer Registry, and the Welsh Cancer Intelligence and Surveillance Unit.

The incidence data in this report relate to children and young people who were residents of the UK, under 25 years of age and diagnosed with a malignant neoplasm or non-malignant CNS tumour included in the International Classification of Childhood Cancer, Third Edition (ICCC-3)2 during 1997-2016.

The cancer classification by Birch and Barr3 has a more detailed classification schema for cancers of epithelial origin (carcinomas) and is frequently used to classify cancers of adolescence and young adulthood. However, the Birch and Barr classification is not sufficiently detailed for the description of cancers of childhood particularly for those cancers that occur in early childhood.

For this report, a decision was made to use the International Classification of Diseases for Oncology, Third Edition (ICCC-3) for all cases irrespective of age, with modifications to adequately classify carcinomas and to allow direct comparison between children, teenagers and young adults.

Langerhans cell histiocytosis and neuroendocrine/carcinoid tumours of appendix were excluded, because they were mostly regarded as non-malignant until towards the end of the study period and registration was consequently not complete. The total number of cancer registrations analysed was 75,103.

ICCC-3 was defined according to codes in the International Classification of Diseases for Oncology, Third Edition (ICD-O-3). For this report, ICCC-3 was modified to accommodate morphology codes that have been introduced in the first and second revisions of ICD-O-3. The classification of carcinomas in ICCC-3 was expanded to cover all the most common sites for these tumours in the TYA age range.

For some detailed analyses, certain ICCC-3 categories were split as follows:

• Ic Chronic myeloproliferative diseases into chronic myeloid leukaemia and other chronic myeloproliferative diseases;
• Id myelodysplastic syndrome and other myeloproliferative diseases into juvenile myelomonocytic leukaemia & chronic myelomonocytic leukaemia and myelodysplastic syndrome;
• IIIa.2 choroid plexus tumours into choroid plexus carcinoma and choroid plexus papilloma; astrocytoma into pilocytic astrocytoma and other astrocytomas.

Part or all of existing categories were combined to create additional categories for brain stem gliomas, optic nerve tumours, Ewing sarcoma family of tumours, and hepatic sarcomas.

For tumours of paired organs, multiple diagnoses of the same tumour morphology (or one that was compatible but less specific) in the same patient with different laterality were converted into a single bilateral case.

The cancer classifications used for this report are listed in Appendix A.