Welcome to health care magic.
1.You have mentioned that your doctor has said there is a
cyst, but not mentioned on what evidence it was said examination or imaging findings, however it been a long time since.
2.Now if you are my patient i would have examine the
scrotum and if any abnormal finding - ask for an
ultrasound scan.
3.Ultrasound scan will help me to know - if there is cyst ( if its simple or complex) or just fluid collection or testicular mass.
4.At the same time status of the testis its vascularity / blood supply can be assessed.
5.Depending on the findings one can narrow down the diagnosis weather it will fit in to the cancer or just a cyst, and condition of cyst after so long - weather complicated or remain unchanged. treatment depends on that. Good luck.
Hope i have answered your query.
Any thing to ask do not hesitate. Thank you.