To start with: my MIL is lovely, we get on really well, her two grandsons love her to pieces and she's generally fab. Not a MIL-bashing thread!
However. She spends a lot of time talking about people she knows who are very ill/dying. This doesn't even have to be anyone she's close to, in fact usually it isn't. (The last two were her sister-in-law's cousin and the daughter of someone who used to be DH's teacher.) She wants to talk and talk and TALK about it. She will phone up or turn up, ask about the DSs for a few minutes, then say "Ooooh, did I tell you the latest on Emma's neighbour's dad? Well, they're saying the cancer's spread to his bones..." and we get a full detailed update on EVERYTHING.
I think she is genuinely upset about these people. She has also lost a few friends and family over the past years and I suppose in some sense she's working through it? And like I say she is genuinely lovely, it's just once she gets on to the Terminal Illness Latest Roundup it's like she can't bloody stop.
I am starting to find this upsetting myself. I'm going through some stressful stuff at the moment, including parent who is ill but undiagnosed. I really don't want to hear stories about somebody else who is just a shell of their former selves and it's so sad. I don't want to hear MIL talking about why it makes no sense to believe in God when such awful things happen in the world, when my religious faith is what's got me through my own awful times 
She also talks about her own death (in quite a matter of fact way, but still a lot). She goes to lots of funerals of anyone she tangentially knows who has died - she says she needs to go to show her support, which I am sure is well intended but is probably not helping her be less doom-and-gloom.
Hints, nudges and changing the subject don't work. And MIL is a very sensitive and anxious person, who would be mortified and massively upset if I got any firmer with her about how it's upsetting me (belieeeeeve me), and I don't want to make her cry. Plus I feel like a cow being all "oh shush now about the teenager with brain cancer, MIL, it's bringing me down!"
ARGH.