Any substance or condition that increases cancer risk is referred to as a risk factor. Cancer of unknown primary (CUP) is a cancer that has already spread (metastasized) when it is found, but doctors don’t know where it started (primary tumour). CUP is not a single type of cancer, but a group of many different types of cancer. Different factors can increase the risk for different types of cancer. This makes it very hard to identify specific risk factors for CUP.
In some cases of CUP, the primary cancer is eventually found. Knowing the type of primary tumour can make it easier to identify factors that are known to develop or may increase the risk of developing that type of cancer.
CUP is more frequently diagnosed in people around age 60.