Annmarie Lewis, 36, from south east London tells us why she's so determined to overcome her own health issues and run the Virgin London Marathon for Prostate Cancer UK.
"I'm running the marathon for my dad, Norman, who was diagnosed with prostate cancer in January 2012 at the age of 65. We were really surprised when we found out because he hadn't had any symptoms and he'd never really been ill.
"While he was having a routine check up, he thought he may as well have a PSA test so he asked for one. He knew about it because previous family members have had prostate cancer. The doctors came back and said his PSA was really raised and sent him for further tests and that's how he got diagnosed.
"He decided to have his prostate removed and volunteered to take part in a clinical trial which meant he also had radiotherapy and hormone therapy. He was fine at first in terms of side effects. His new wife had given birth to a little boy during the treatment and that helped him stay feeling young and positive.
"Thankfully, he was given the all clear this year though he's still getting side effects, which he's finding more difficult now. They're sending him for tests and finding ways to help him manage this and Dad's a very strong person - he isn't going to let it get him down.
"We first heard about Prostate Cancer UK while Dad was going through treatment. It was a fantastic support. Dad called the Specialist Nurses for support and was able to speak to other people with the disease. He was also directed to help with his financial situation, which was quite difficult as he couldn't work and his wife was pregnant.
"The services really helped me too. Me and Dad are really close and looking at the information on the website made it a lot less scary. Everything was so clear and easy to understand. It made it easier to talk about positive and practical things with him as opposed to thinking: 'Oh my God is he going to die?'
"I decided to run the marathon for Prostate Cancer UK because I just felt I had to do something. The research they fund is really important and we need to raise awareness of the fact that African Caribbean men are three times as likely to get prostate cancer as white men.
"I hadn't done any long distance running before, but I thought if Dad was brave enough to take part in a clinical trial that then maybe I could do a marathon. I also wanted the challenge of trying to overcome my own health issues. I have osteopenia, which basically means I shouldn't be able to run that far. It affects your joints, your hormones and your muscles. I don't like being told I can't do things so I was pretty determined. And the doctor said as long as I trained properly and ate properly it should be okay.
"The training has been a bit gruelling, partly because of how bad the weather's been. There have been days when it's just been too icy to go out. But I do enjoy it and get a real sense of achievement. When I did my first run over 10 miles, I found myself feeling very emotional afterwards. I did my first 20 miles the other week and managed to do that in the five hours so I'm hopeful that I will get the 26 miles done in seven hours.
"Dad will be coming to watch. He was a bit shocked by it all and can't believe I would want to go and do that, but he is so proud. I'm very nervous but I am looking forward to it. I've done most of my training by myself, so it'll be really good to run with other people so we can motivate each other.
"I'm really, really close to my dad and I love him so much. There couldn't be any better inspiration for me to get out and run. It's almost like I'm getting my own back on cancer."