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Frequently asked questions about CUP

Q. How is CUP actually defined?

A. Histologically confirmed metastases with no identifiable primary site. That is to say, tissue taken from the site of a suspected secondary confirms that it is cancer, but when studied under the microscope and chemically tested the sample cannot be matched with that of a primary cancer.

Q. How many people are diagnosed with CUP?

A. It is very difficult to find an accurate picture. The number of cases of confirmed CUP that are diagnosed each year can be estimated using the International Classification of Disease (ICD) codes ICD-10 C77-80. The latest figures available in 2020 show about 8,000 new cases of CUP registered in the UK  (in 2006 when the charity began there were about that number in England alone and the numbers are falling each year as patient management and diagnostic techniques improve). As there is no discrete ICD code for CUP, there may be additional CUP diagnoses that are not captured in these codes.

Q. What makes the source of this type of cancer undetectable?

A. There are a number of possibilities but the scientists are not sure. It is likely that a primary tumour in a CUP patient has spread while it is very small and has either self healed or been expelled from the body after it has spread, for example if it was hanging perilously to part of the digestive system; or if it remains, and it may be as small or smaller than a grain of rice, it is too small to be picked-up by present day tests including ultrasound, CT scans, MRI and PET.  The secondaries, if growing close to the primary, may make it difficult to distinguish from a larger cancer mass. The primary may have been attacked successfully by the body’s immune system as it tries to get a toehold and migrated through the body to find sanctuary in a place where it can thrive and confuse the immune system.

Q. Does the fact that the origin is unknown make it harder to treat?

A. Yes –  it is generally accepted that knowing the origin of the cancer can improve the outcome for the patient because therapies can be targeted to the specific cancer type. Cancers are named and treated according to their primary site, regardless of where they have spread in the body. The cancer cells that have spread are still those of the original cancer cells and need to be treated accordingly.

Q. Do people with CUP face any unique challenge not faced by other cancer patients?

A. Of course, because the unknown/ uncertainty creates an added level of anxiety. CUP is a challenge for clinicians as well as patients and their loved ones. Diagnostic uncertainty is communicated to patients who have difficulty understanding the condition and making sense of the different tests used during the investigative process. This may lead patients to question  clinicians’ ability to treat them. We have researched this in some detail and the findings can be seen in this paper.

Q. Does CUP affect children?

A. It is most often found in people who are in their 60s and over but it can affect people of all ages; incidence for children in the UK  is 1% or less.

Q. Distinctions are often made between Carcinoma, Sarcoma, Melanoma or Lymphoma  as the main Cancer Classifications  – where does CUP fit in?

A. Most cancers of unknown primary are Carcinomas – carcinomas of unknown primary. Unlike Carcinoma, Sarcoma, Melanoma & Lymphoma have a characteristic histology allowing treatment without the need to locate a primary. Carcinomas are tricky and it is important to try and find the primary, which could be in several different places, to target treatment. There are clear management and treatment paths in place within the NHS to deal with sarcoma, melanoma, and lymphoma in all their manifestations (localised or metastatic). This is not yet the case with carcinoma of unknown primary.

Q. What proportion of all cancers is CUP?

A. In the UK and USA most sources seem to come out at between 2- 5% . It does depend on how CUP is defined and recorded. Estimates of the proportion of CUP in some developing countries can exceed 10%. Taking a world-wide view, it is widely accepted to be one of the 10 most common cancer types.

Q. Diagnostic techniques presently lead to the primary being found in how many of those who are initially categorized as having CUP?

A.  It depends on the sub-set of CUP that is diagnosed e.g. Adenocarcinoma, Poorly Differentiated Cancer (explained in CUP classifications). The most pessimistic view is that the primary tumour is found in only 20% of cases. But figures vary significantly and this reflects the problem of how the statistics are gathered and the definition of CUP. Of course, once a primary is found it is no longer CUP.

Q. If you present with secondary cancers (metastases)  does that mean you have CUP?

A. No. Some 10-15% of cancer patients in the UK  present with metastatic cancer.

Q. What are the commonest sites for metastases?

A. Lymph nodes, liver, bones, lungs.

Q. I have heard the expression “true CUP”. How does this fit with other CUP definitions?

A. CUP is a complex and very varied phenomenon and it is therefore difficult to make simple distinctions that are also accurate. True CUP is a way of showing the point where all the tests that can be done, or it is desirable to do, have been completed and the doctors still do not know with any confidence where the cancer has come from. You could equally well view this as confirmed CUP. Up to that point, while tests are going on, or doctors have a good idea of where it might be, it is a state of undiagnosed, uncertain, undetermined, or unconfirmed CUP. These are not medically recognised terms in the CUP journey but they may help in understanding the problem.

Q. You have stressed the need to find the primary to target CUP but is there no way of treating CUP in general?

A. This is an area of research and ’empiric’ chemotherapy (an oncologist’s best guess on the evidence available) may well have an effect on the secondaries; but for the best results most oncologists believe it important to find the primary in treating carcinomas. Molecular science can help. ‘genomic profiling’, which is not generally available on the NHS except for those on a trial, may help find the molecular primary (the tissue of origin) or the molecular target (actionable genetic mutations) for better therapy. There is a school of thought that CUP has a specific biological entity and if we could understand better the biology of cancer tumours the name of the cancer would be less important than its characteristics for determining treatment.

Q. Where does research show the most common primary sites when it is found?

A. Usually shown to be: lung, pancreas, biliary tract, gastrointestinal tract; but genetic profiling is beginning to question these findings.