Is adenocarcinoma life threatning?

Depends. Adenocarcinoma is a cancer, left untreated it is life threatening, in some cases even when treated, depends on where it is, what grade, if it metastasized, and a lot of other conditions. Doctor that diagnosed it will be the best to answer the question as he/ she will have or will be able to obtain all nessesary information.
Most definitely. I hope your doctor told you how serious this is, and how important early treatment be instituted.