What makes you think the tren lowered you immune system. I am not aware that it depletes white blood cells, CD4 or CD8 cells or TNF and have not seen any data that shows any teratogenicity associated with AAS use. My guess is that if it is skin related, then you can blame the sun or your tanning bed. Skin cancers are very common, especially if you get a lot of syun exposure and have a light complexion.
Good luck. Most skin cancers can be treated easily if caught early.