Schitzo, They are tumors and they are not uncommon. I have fond more in chinook and chums which I think addresses there longivity more than any thing. My theory the older the fish the more its chances to win the tumor lottery.
Not really sure how much of a hand polloution plays in the growth and development but I have seen studies that indicate a higher number in populations that are resident and adjacent to large pollouting industrial sites. Could be coincedental but then so could the rate of cancer victims down wind of Chernobyl.
Just an after thought the two canidates running for President one wants to gut the clean water and air act do you Vote there is still time to register and vote .