This page outlines the different ways in which NDRS defines ‘All malignant cancer’ and the reasoning behind each definition.

How does NDRS define ‘All malignant cancer’?

NDRS present three main definitions of ‘All malignant cancer’ to suit different needs (1a, 1b, and 1c below). Each definition of ‘All malignant cancer’ excludes some cases of skin cancer, and these skin cases are instead counted in the corresponding ‘Excluded skin’ definition (2a, 2b, and 2c below). NDRS also present a ‘Publication total’, defined in point 3 below.

  1. NDRS definitions of ‘All cancer’
    1. ‘All malignant cancer excluding NMSC (ICD-10)’ is defined in ICD-10 as neoplasms coded between C00 and C97, excluding C44.
    2. ‘All malignant cancer excluding BCCs and cSCCs (ICD-O3)’ is defined in ICD-O3 as neoplasms with behaviour code 3, 5, 6, or 9, in the version of ICD-O3 in which they were registered, excluding BCCs and cSCCs (coded to lip or skin sites in ICD-10).
    3. ‘All malignant cancer excluding BCCs (ICD-O3)’ is defined in ICD-O3 as neoplasms with behaviour code 3, 5, 6, or 9, in the version of ICD-O3 in which they were registered, excluding BCCs (coded to lip or skin sites in ICD-10).
  2. NDRS definitions of ‘Excluded skin’ (skin cases excluded from definitions in point 1)
    1. ‘All non-melanoma skin cancer (NMSC) (ICD-10)’ is defined in ICD-10 as neoplasms coded to C44.
    2. ‘All BCCs and cSCCs (ICD-O3)’ is defined in ICD-O3 as neoplasms coded to BCC or cSCC morphologies* at lip or skin ICD-10 sites, counted using the 1st per person per annum (1stPPPA) method.
    3. ‘All BCCs (ICD-O3)’ is defined in ICD-O3 as neoplasms coded to BCC morphologies* at lip or skin ICD-10 sites, counted using the 1st per person per annum (1stPPPA) method.
  3. The ‘publication total’ is defined as the sum of the incidence in each of the individual cancer site groups presented in the defined output. [See the last section of this page for an expanded explanation of the ‘publication total’]

* ICD-O3 morphology codes relating to BCCs and cSCCs can be found in the skin section of the ‘NDRS cancer group definitions’ downloadable items from the Standard cancer group definitions page.

The counts from corresponding pairs of definitions between point 1 and point 2 above can be summed to give an ‘All malignant cancer’ definition which includes all skin cancer (i.e., 1a+2a, 1b+2b, or 1c+2c). Note that 1b+2b and 1c+2c will give the same total which can be thought of as the ICD-O3 definition of ‘All malignant cancer’ whereas 1a+2a gives the ICD-10 definition of ‘All malignant cancer’.

For more information about these totals, including why we publish three different counts for ‘All malignant cancer’ based on different coding systems, and excluding different skin cancer cases, please see the information below.

Why does NDRS present different definitions of ‘All malignant cancer’ in two different coding systems?

Historically, cancer was coded in ICD-10 using C codes to represent malignant neoplasms, and D codes to represent in situ neoplasms, benign neoplasms, and neoplasms of unknown or uncertain behaviour. The international classification of diseases for oncology (ICD-O) was first released in 1976 and is now on its third revision (ICD-O3) which has subsequently had two updates. In ICD-O3, malignancy is defined by a neoplasm having behaviour code 3, 5, 6, or 9 (representing some version of the neoplasm being malignant), with behaviour codes 0, 1, and 2 representing benign, unknown or uncertain behaviour, and in situ neoplasms, respectively.

The National Disease Registration Service (NDRS) has been one organisation since 2013 when the regional cancer registries merged. At this point, there was a central push to register neoplasms in ICD-O3, the preferred and most up to date coding system for cancer. Many other national registries still code in ICD-10 however and hence for the purposes of comparison and for historical reasons, we present counts of ‘All malignant cancer’ defined both in terms of ICD-10 coding (where we exclude NMSC), and in terms of ICD-O3 coding (where we exclude either BCCs and cSCCs, or BCCs only). Generally, the count of malignant cancers using the ICD-O3 definition is greater than the count using the ICD-10 definition, by approximately 6000 tumours a year, from 2013 onwards. This is a percentage difference of around 1-2%. There are three main reasons for the difference in counts of malignant neoplasms between the two coding systems.

  1. Neoplasms which were classed as non-malignant in ICD-10 are now thought of as malignant and hence have behaviour 3, 5, 6, or 9 in ICD-O3. This positively contributes to the higher count of malignancy when it is defined in ICD-O3.
  2. Diseases and conditions which were not thought of as cancer at all in ICD-10 are now classed as malignant cancer in ICD-O3. This positively contributes to the higher count of malignancy when it is defined in ICD-O3.
  3. Conversely, there are some neoplasms which were classed as malignant in ICD-10 which are now thought of as non-malignant and hence are behaviour 0, 1, or 2 in ICD-O3. This negatively contributes to the higher count of malignancy when it is defined in ICD-O3.

The biggest contributing factor is that several haematological neoplasms which were D coded, and hence non-malignant, in ICD-10 have behaviour code 3 in ICD-O3. These are conditions such as polycythaemia vera, myelodysplastic syndromes, refractory anaemia, essential thrombocythaemia, primary myelofibrosis, and other myeloproliferative conditions. A smaller number of neuroendocrine tumours and sarcomas also have a behaviour change between ICD-10 and ICD-O3, where they are thought of as malignant in the latter system. There are a few conditions which were not thought of as cancer at all in ICD-10 but have been introduced as neoplasms in ICD-O3. Again, these additions are primarily haematological neoplasms such as Erdheim-Chester disease and monoclonal B-cell lymphocytosis. As of 2022 diagnoses, these additions account for very few tumours as a proportion of the total number of malignant neoplasms. There are also some tumours, most notably borderline ovarian tumours, which were thought of as malignant in ICD-10, but are no longer classed as malignant in ICD-O3. This type of behaviour change also affects a smaller number of brain and kidney tumours, amongst others.

The reasoning behind the difference in count of ‘All malignant cancer excluding…’ when using the two different coding systems should be considered when choosing the most appropriate count for a specific use case. NDRS believe that the ICD-O3 definition is the most up to date, clinically meaningful definition, however the ICD-10 definition may better align with historical publications and publications from other countries.

Why are some skin cancers excluded from ‘All malignant cancer’ and how are they defined?

Skin cancer accounts for a large proportion of all cases of cancer diagnosed per year. Historically, skin cancer has been thought of in two categories

  1. melanoma skin cancer, and
  2. non-melanoma skin cancer (NMSC),

with the latter accounting for vastly more cases per year, and the former having significantly worse outcomes. Often, NMSC requires minimal treatment (it is often resected with no further treatment required) and historically NMSC patients were not always treated in secondary care. For these reasons, when citing figures of ‘All cancer’, NMSC is often not included. When included, there will be a dramatic increase in the number of cancer cases diagnosed per year, and a dramatic increase in the overall survival rate of ‘All cancer’, for example. Dependent on the use case for defining ‘All cancer’, it may make sense to include some, or all, skin cancers, however.

In ICD-10, NMSC is defined as all cases coded to C44, and melanoma skin cancer (which is always included in the ‘All cancer’ definitions) is coded to C43. In ICD-O3, we can look in more detail at the cases coded to C44 in ICD-10, where they split into three main groups; Basal cell carcinomas (BCCs), Squamous cell carcinomas (cSCCs), and ‘rare’ skin cancers. BCCs and cSCCs are collectively known as ‘keratinocyte cancers’. The ‘rare’ skin cancers include cases such as ‘Merkel cell carcinoma’, and ‘Cutaneous sarcoma’. Whilst these cancers are non-melanoma, they can have worse outcomes and more complicated treatment pathways than BCCs and cSCCs and so the current line of thinking is that they should not be categorised with keratinocyte cancers. The ICD-O3 versions of our ‘All malignant cancer’ definitions therefore exclude only the BCCs and cSCCs (definition 1b), or exclude only the BCCs (definition 1c) and keep the rare skin cancers in the definition along with the melanomas. In some use cases (such as comparing with Cancer Wait Times (CWT)), it may be appropriate to exclude only the BCCs (definition 1c) rather than both the BCCs and cSCCs (definition 1b) of skin. cSCCs are generally thought to have worse outcomes than BCCs.

Keratinocyte cancer is defined by NDRS as all registered BCC and cSCCs of skin and all subsequent BCCs and cSCCs of skin identified as proxy registrations from pathology reports and counted using the 1st per person per annum (1stPPPA) method. The cancer registry only fully registers the first BCC and cSCC of skin and standard methodology is followed to identify later BCCs and cSCCs, based primarily on pathology reports received by the registry. Tumours are classified as BCCs and cSCCs based on their ICD-10 code and ICD-O3 morphology codes. For more information see the Skin tumours section of the ‘NDRS cancer group definitions’ downloadable items from the Standard cancer group definitions page.

The vast majority of registered BCCs and cSCCs are coded in ICD-10 to the NMSC site C44. BCCs and cSCCs can however also grow on the external lip, and the external genitals, where they might be mapped to the ICD-10 code for lip or genitals rather than C44. In the definitions 1b and 1c, only BCCs and cSCCs coded in ICD-10 to skin or lip sites are excluded, whilst BCCs and cSCCs coded to the external genitals are kept in the definition. Conversely, in the ‘Excluded skin’ definitions 2b and 2c, cases of BCCs and cSCCs coded in ICD-10 to skin and lip site are included whilst those coded to external genital sites are excluded.

What is the ‘publication total’ (definition 3) and why is it different to the sum of any pair of ‘All malignant cancer’ and ‘Excluded skin’?

The ‘publication total’ is the sum of incidence in all the individual site groups presented within a given publication. It can be used as a reference number to put the counts for specific cancer sites into perspective. The publication total may differ between NDRS publications and may also differ from the sum of any pair of ‘All malignant cancer’ and ‘Excluded skin’ definitions. There are four main reasons why this might be the case.

  1. Most publications do not publish on specific cancer site groups which account for all (malignant) cancers. For example, NDRS register cases coded to non-specific ICD-10 C codes such as C76 for ‘Other and ill-defined sites’. These tumours will be counted within ‘All malignant cancer’ (definitions 1a, 1b, and 1c), but not within the ‘publication total’. Some publications also do not publish on cancer sites where the incidence count is very low, for information governance reasons. Again, these tumours would be counted within ‘All malignant cancer’ (definitions 1a, 1b, and 1c), but not within the ‘publication total’.
  2. Some publications specifically publish on a subset of cancers such as those which receive a certain type of treatment. This means that the ‘publication total’ will also only encapsulate those tumours treated in a certain way and hence the ‘publication total’ is likely to be lower than the sum of any pair of ‘All malignant cancer’ (definitions 1a, 1b, and 1c), and ‘Excluded skin’ (definitions 2a, 2b, and 2c).
  3. Many outputs publish on specific cancer site groups which include non-malignant cancers by their definition. For example, the NDRS ‘Brain’ definition includes both malignant, and non-malignant, brain tumours. The non-malignant cases account for approximately 50% of the whole ‘Brain’ group each year. Likewise, the NDRS ‘Bladder’ group is comprised of approximately 50% malignant tumours and 50% non-malignant tumours (regardless of the coding system used to define malignancy). These definitions were decided upon with cancer site specific clinicians and charity partners. The non-malignant tumours within specific cancer site groups will therefore count towards the ‘publication total’, but not the sum of any pair of ‘All malignant cancer’ (definitions 1a, 1b, and 1c), and ‘Excluded skin’ (definitions 2a, 2b, and 2c).
  4. Some publications include cancer sites such as sarcomas and neuroendocrine neoplasms (NENs), which can occur at many bodily sites and hence overlap the other cancer sites groups (such as breast, bowel etc). This means that these tumours will be counted twice within the ‘publication total’ but counted only once within the sum any pair of ‘All malignant cancer’ (definitions 1a, 1b, and 1c), and ‘Excluded skin’ (definitions 2a, 2b, and 2c).

Appendix - Illustrative counts for the ‘All cancer’ definitions

This appendix gives an example of the totals for ‘All cancer’ (definitions 1a, 1b, and 1c), ‘Excluded skin’ (definitions 2a, 2b, and 2c) and the ‘Publication total’ for the NDRS cancer incidence statistics. The table below shows the counts for the 2022 diagnosis year.

The figure below shows the counts for each definition (as presented in the table above) for the diagnosis years 2019-2022.