What Causes Rhabdomayosarcoma In The Testicle Of A Child?

my son was diagnosed with rhabdomayosarcoma in his right testicle in dec 2008. we was 5yrs old. it was stage 1 and had the testicle removed no other signs anywhere else, he did chemo for 6 months , and has been great since then. dec 10/2010 ct scan showed left hilar node in medinastal , enlargment to 11 mm. what are the chances of this being cancer? he has been cancer free for 18 months since end of chemo. in the last 6 month he has had chicken pox, with secondary infection, streap throat and ear infection as we speak, also has some exema spots on his legs. going to do biopsy but sugery sounds scary because they might not be able to get it with scope and might have to cut him open and spread the ribs. very worried parent !! thank you