Hi Silvio, I am NOT a doctor, but I do understand medical terminology so I will try to explain it in a very basic way... to really know what this means FOR YOU is to speak with your doctor.
First: the word Atypical means Not Typical... I believe that Mart1 is a specific type of lab test done on a tissue sample. Now the IMPORTANT thing to realize is that Atypical does not mean bad or good... it means it's "different" looking. What is important is talking with your doctor to see what he/she wants to do to get more information on this area.