I left neutering my Elkhound bitch later than I thought I would but still early enough to prevent pyometra and not too much worry about anaesthesia as she's fairly fit 8 years young.
Devastatingly, they couldn't do the ovariohysterectomy - spay - as she's tumours on both ovaries, one of which is very large, and too close to her kidneys.  Ironically, they couldn't do the op that would've been the cure because she's got the tumors.
I've discussed with 2 vets - and decided on not giving her chemo - I've seen too much pain with this - just going to try to give her the best life I can whether it's 6 weeks (she's way over that) 6 months (nearly halfway) or 6 years (please). 
My major worry is not knowing when she's in too much pain - not yet by any means - she always know when I am.  Why can't I be as clever?

So sorry what a terrible shock for you .

You will be able to tell if she is in pain she will let you know.

I hope what time you have left with her you will  be able to look back with fond and happy memories x

So sorry, that is very young  for an Elkhound

Elkhounds are very stoic, which is why the three I have lost have given little sign of illness, and been gone suddenly or in days. 

My friend Vanessa who posts here only found her boy was a bit off showing in veteran at Crufts the year before last, and he had cancer of the Spleen and was gone in days.

Loss of appetite and disinterest in going for walks, and you have to question if they are in pain.

So sorry.

So sorry. The day I said good bye to my dog Varg you would not have know there was anything wrong, his gastric cancer had progressed to such an advanced stage that he was unable to eat but he was as bouncy as ever. But you will know when the dog has had enough, I usually ask myself if the dog is still enjoying more than 50% of their life if the answer is no the time has come to offer your dog the most positive act of love you can and let them go.

Thank you all for your kind words.  I found out 13th Nov last year. I sort of wish I hadn't 'cos I worry about everything now.  Heidi is very happy, still loves her food, walks  cuddles, if she went off any of those I'd definitely worry.  She isn't any different.  One vet did say it was possible it/they could just stop growing on their own.  I live in hope!

I'm sorry for your losses.  It's so hard on us who're left behind when it happens so quickly, but o so much better for them than a long drawn out painful illness.
I do worry that she's so stoical I won't know she's in pain.  I've been looking it up and it talks about subtle signs like taut forehead, slightly hunched, changes in drinking and weeing.  Anyone know any others?

The eyes would be a giveaway for me.
I hope you get a lot more quality time with her.

Don't worry, you will know I promise you

Agree with WolfieStruppi

It is a dead giveaway in their eyes.  I feel quite choked typing that, but they know how to tell you.