Hi and welcome to HCM.
I am not sure are you talking about lesion in lungs or in mediastinum. It is hard to know exact diagnosis, but I disagree that the cancer is first thing to think of. Medisatinal masses include various of possible lesion such as swollen lymph
node, tymus parnchyma, bronchogenic cysts and many others. CT can show tumor
or any kind of mass, its density,shape and progression. Knowing this doctor can guess is there possibility that this is cancer. It is never 100% sure and only biopsy
can prove it,but i wouldnt recommend it in your case.
Of course if you have symptoms,if you smoke and considering your genetics this is something that shouldnt be ignored. I suggest to wait and see will it increase in 4-6 months,and then repeat CT scan
. Nothing will happen in short time. Wish you good health.