[Multiple primary cancer. Presence of more than 4 primary cancers]

The presence of more than four primary malignant tumours in a single patient was investigated in the Danish Cancer Registry. Four patients with five primary malignancies and one patient with six primary malignancies were found. All of the tumours were verified histologically and there was convincing evidence that none of the tumours were secondaries. In some of the cases, clustering of tobacco-associated cancers was observed. The anticipated number of cases with more than four primary malignancies was computed and it was found that less than one case would be anticipated. It is concluded that some cancer patients have an increased risk of developing a new primary malignancy.