CAS Explorer enables researchers & analysts to get a better understanding of the Cancer Analysis System database.

CAS Explorer shows the completeness of the cancer registration data registered by the National Cancer Registration and Analysis Service (NCRAS) in Public Health England (PHE). It is designed to be used by researchers and analysts to gain a better understanding of the data quality and completeness of the fields in the three main tables before submitting requests to NCRAS or the Office for Data Release (ODR). For a more granular exploration of the data the Simulacrum can be used to see what sort of analyses are feasible.
There are three main tables that hold cancer data. One relating to patients, one to tumours and one to treatments. The ‘tables’ option allows you to see the completeness of each field in these three tables. For example, you can see how many tumours have a stage value.
Field List
A list of fields and in which table they appear in.
Type of Tumour
Completeness of fields in the tumour table with the option to select the tumour types. Provides numbers for the whole time period combined.
Registry Areas
Completeness of fields in the tumour table split by cancer registry areas. Provides numbers for the whole time period combined.
Time Periods
Completeness of fields in the tumour table related to the selected diagnosis year. Provides numbers for all cancer types combined.
Shows which tables and columns relate to specific subject areas: e.g. treatments, diagnosis and geographical location.

Data Source

CAS Explorer is currently showing data from the snapshot taken in February 2019. A snapshot is a copy of the registry data at a specific time. A snapshot taken in January does not mean the data will be complete up to that date as cancer registration is an ongoing process.

About the data

CAS Explorer presents the completeness of fields within the tumour, patient and treatment tables held within the Cancer Analysis System. The tables contain details on patients with finalised malignant tumours (ICD10 O2 C00-C97 excl. C44) diagnosed between 1995 and 2016 and resident in England. Duplicates have been excluded as well as cases where the patients sex does not agree with the cancer site they are registered with e.g. a women with prostate cancer.

On the tables tab, it is possible to filter the tumour and treatment table fields by year of diagnosis and cancer type to give a more accurate idea of completeness if your request only covers a particular time period or cancer site. If more than one year or cancer type is selected then the figures will be added up to produce total counts. Incident cases of cancer are counted for each separate primary tumour; one person may be diagnosed with more than one primary tumour and would then appear twice in the incidence statistics; secondary tumours and recurrences of a previous cancer are not counted as new incident cases. It is worth noting that the completeness of some fields has increased over time, so the overall figures may average out these differences.

Completeness is defined separately for each field depending on its contents. Records included as missing will include ‘not known’ codes and null values (where the field has no information of any kind). The totals for each field will also depend on the field. In many cases it will be out of the total number of rows but in some cases a field only applies to a limited number of cancers e.g. the Gleason grade is only relevant to prostate cancer diagnoses.

Each field included in the Simulacrum is marked with a green flag in a column named ‘in Simulacrum’ on the tables page.

What to be cautious of when using the tool

  • The numbers of cases associated with each tumour type might differ from results published elsewhere. This tool should only be used for its intended purpose - that of getting an approximation of the completeness of fields within CAS. For detailed statistical enquiries please contact
  • The cancer registration dataset is being continually updated so figures can change with each update – including adding more recent data and for numbers in the past.
  • Various quality criteria are applied to the data – for example, only confirmed diagnoses are included.
  • Counts less than 50 are suppressed to preserve patient confidentiality.
  • Please note the completeness of stage_best measured here includes values indicating that the tumour did not have a staging system or that there is currently insufficient information recorded. Therefore, this should not be considered a measure of how many tumours have a known stage

More information on the background and development of CAS Explorer