I had a close friend who fits this category. Every high profile disease would become hers. She had cancer (never treated), MS (never treated and mysteriously vanished), a brain tumour (ditto)
She would also pretend her small daughter had been diagnosed with things. In fact we bonded over discussions about a life threatening congenital problem that my child had two operations to correct. Whereas her daughter's went away all by itself and was never mentioned again.
She once claimed her NT three year old had Down Syndrome and spent the afternoon having hugs and sympathy from her friends while I sat back and watched in horror. The newly revealed DS was mentioned again...
My fave, and the one that really showed me how messed up she was, was when I had an incoherent, sobbing phone call from her asking me to come at once.
Her auntie had died after a short term illness. The family had, she told me between sobs, kept it from her because because they knew how badly she would take it. I felt terrible for her because she was very close to her aunt and, indeed, I had had coffee with the woman a couple of days before so was quite shocked myself. So I made tea, cleaned the house, walked the dog, picked up the kids.
The tears went on all day but little details began to niggle at me so I eventually, after a whole blinking day running around. carefully asked her if we were talking about Auntie X. Oh no, she said, it was Auntie Y.
I didn't know you had an Auntie Y, I said. That's because I haven't seen her since I was six, she replied. And now I never will, wail wail...
We aren't friends any more but her FB page always gives me a chuckle 
And, as someone said earlier, she was very proud of being a Leo. So make of that what you will.