Prognosis in cancer of unknown primary vs a known primary site

Is the prognosis in cancer of unknown primary worse compared with cancer with a known primary site?

Nicholas Pavlidis: If we divide cancer of unknown primary into two big groups, one group has the so-called good prognosis subsets and the other one has the poor prognosis. However, the poor prognosis is something like 80% of all cases.

If we are talking about the good prognosis, most of the cases have exactly the same prognosis as the primary ones. For example, axillary lymphadenopathy looks like breast cancer, squamous cell carcinoma of the neck looks like advanced head and neck [cancer], peritoneal carcinomatosis looks like ovarian cancer. These [types] of cancer of unknown primary are more or less of the same prognosis.

But if we go to the major part, which is the 80% that have the bad prognosis, my personal opinion is that these patients are carrying a different clinical behavior, and of course they have some biological markers, like chromosomal instability, which is not equivalent to the known primary ones. In other words, I would say that the poor-prognosis patients are, by definition, having at least a worse prognosis then the known primary ones.