I never heard this about autoimmune disorders and cancer; in fact, I heard that chronic inflammation might increase cancer risk. BUT, anecdotally, the longevity in my mother's family is wild... while, at the same time, so is the incidence of (a potpourri of) autoimmune illness. Even my grandmother, who had breast cancer twice (in her 40s and in her 70s) is now 88 and going strong... with, simultaneously, decades of autoimmune conditions.

So I would not be surprised if this were true. ;)

Wishing you health!