Epidemiology
Cancer will often present as a result of symptoms due to the primary site of the tumour, but sometimes the cancer is able to metastasise before the primary site is large enough to be detected. In contrast to known primary tumours, carcinomas of unknown primary (CUP) tend to have early dissemination, unpredictable metastatic pattern, aggressive nature and an absence of symptoms from the primary site. CUP is therefore defined as the detection of one or more sites of metastatic tumours for which investigations have failed to identify the primary site.
Up to 5% of all cancers are from an unknown primary, representing eight to 20 patients per 100 000 of the population per year. It is the seventh most frequent form of cancer and fourth most common cause of cancer death in both males and females. The median age at presentation is 60 years and 50% of patients present with multiple sites of involvement, with the rest having a single site in: liver, bones, lungs, or lymph nodes.
Aetiology
The usual histological diagnosis is that of adenocarcinoma or poorly differentiated carcinoma. Different tumours will spread in different patterns and this may be related to the chemokine and chemokine receptor expression by the tumour and stromal cells.
Clinical presentation
The clinical presentation will depend on the location of disease sites, but most patients (97%) have symptoms at metastatic sites (Table 28.1). Non-specific symptoms such as anorexia, weight loss and fatigue are common. See Chapter 10 for approach to clinical examination.
Investigations and staging
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