Nevoid basal cell carcinoma syndrome, i was diagnosed with a brain tumour when i was 3 (i'm 16 now), would it be possible for me to have nevoid basal ?

You would know it.: It's possible, but you would have had multiple skin cancers as a result of sun exposure through your lifetime so far. You might also have a big head, little spots on your palms, and cysts in your teeth and jaw. But if you have not developed skin cancers, you probably don't have it. (See pic). This is also called Gorlin syndrome FYI.