The double gold medal winner spoke out as it emerged that more than half of British adults could not name any symptoms of the condition, despite it being one of the most commonly diagnosed cancers.
One in 19 people will be diagnosed with blood cancer, according to the charity Bloodwise, while it is the third biggest cause of cancer deaths.
Dame Kelly described how her whole family was shocked when her mother Pam Thomson, who she called Mother Dear, was diagnosed with myeloma at the end of 2014.
She said: “When she was diagnosed it was a big shock, because, one, I think no one had heard of myeloma. We didn’t really know what it was or understand what it was.
“And secondly, to say ‘you’ve got cancer’, isn’t a thing you want to hear with anyone.
“My mum always had a real strong mind and was positive, really, really positive about it, mainly because the consultant was brilliant, and said, ‘these are all the treatments. We can just keep trying. If one doesn’t work we’ll go on to the next one’.”
Her mother had chemotherapy and had a stem cell transplant, which initially made her feel much better, but she died suddenly while in hospital on August 7 last year, aged 64.
Dame Kelly said it was “brilliant” to be the official ambassador the Make Blood Cancer Visible campaign.
She said: “The reality is that so many people that you walk past in the street, so many people of your friends and family, will get a cancer of some description.
“And the thing that we’re trying to bring with the Make Blood Cancer Visible campaign is the realisation that, actually, so many people could be walking around with an illness who won’t know.”
Describing the struggle her mother – who was 17 when she had her – went through, she said: “Watching the deterioration and watching someone cry who never normally cries is quite heartbreaking.”
Talking of her childhood, which saw her live in a children’s home until she started primary school, she said: “I realise how much she fought to keep hold of me. That made me realise how strong a character she was.”
Dame Kelly, who won gold in both the 800m and 1,500m at the Athens Olympics in 2004, described how hard the bereavement has been. “I’ve struggled with it badly,” she said.
“I’m quite open on my social media about how I’m not coping with it, but equally I think it’s important to get the message out there that there are so many people out there that are going through this, especially with blood cancers that are not so well known.”
Blood cancer is the fifth most common cancer in the UK, made up of more than 100 different sub-types including leukaemia, lymphoma and myeloma.
It affects more than 240,000 adults but patients often require more visits to their GP before being diagnosed than those with other cancers, leading to concerns that these delays could hit people’s chances of survival.