You can't judge a book by its cover or a tumor by its expression profile.

Expression profiling has shown great promise in matching cancers of unknown primary to likely primary tumors of origin based on patterns of mRNA expression. However, it remains uncertain as to whether even well matched tumors will demonstrate the clinical features, such as rate of progression, of their matched counterparts. In this case report, we note that based on histology, immunohistochemistry and expression profile this patient's poorly differentiated neuroendocrine tumor would have been expected to grow very rapidly on no therapy. Instead, this cancer was very indolent, with only very little radiographic progression over several years. We believe this report represents a remarkable case of a tumor where features, including expression profile, would not at all have accurately predicted the clinical course seen. While some series have suggested that matching by expression profiling predicts outcome, this case shows a dramatically different result.