Melanoma T3 N2

I had a small piece of melanoma skin cancer removed with 3 under arm lymph nodes  

2 off the nodes showed some cancer   Had a ct scan two weeks ago showed all clear 

I was at the cancer centre yesterday they want to give me the injection every 6weeks 

I am very physically fit and have no other ailments  and don’t take any type of medicines 

the doctor and the nurse explained all the side effects that could happen ,

 I was dumbstruck to put it lightly  just now I am undecided wether to go ahead with the treatment 

anyone give some advice please  I am 71 yrs old