When in a patient more than one tumour in the same or a different organ is diagnosed, multiple primary tumours may be present. For epidemiological studies, different definitions of multiple primaries are used with the two main definitions coming from the project Surveillance Epidemiology and End Results and the International Association of Cancer Registries and International Agency for Research on Cancer. The differences in the two definitions have to be taken into consideration when reports on multiple primaries are analysed. In this review, the literature on multiple primaries is reviewed and summarised. Overall, the frequency of multiple primaries is reported in the range of 2-17%. Aetiological factors that may predispose patients to multiple primaries can be grouped into host related, lifestyle factors and environmental influences. Some of the most common cancer predisposition syndromes based on a clinical presentation are discussed and the relevant genetic evaluation and testing are characterised. Importantly, from a clinical standpoint, clinical situations when multiple primaries should be suspected and ruled out in a patient are discussed. Furthermore, general principles and possible treatment strategies for patients with synchronous and metachronous multiple primary tumours are highlighted.
Keywords: Multiple primary cancer; epidemiology; genetic predisposition; multiple primaries; second cancer; secondary primary.