By Alison Freeman
BBC News, London
About 15,000 women, and men, dressed in bras will walk a marathon route on Saturday night to raise money for research into breast cancer.
Miss Stevenson decided to travel the world after treatment
Many of the walkers have been touched in some way by the disease, like a group of friends who are taking part after Emily Stevenson, from Battersea, south London, was diagnosed with breast cancer aged just 29.
My boyfriend found a lump in my breast when we were on holiday in Rome.
It's one of those things a woman doesn't want to hear, so I pretty much dismissed it until a week later when I felt it myself and panicked.
My GP was really reassuring and told me cancer was uncommon in a woman my age.
He said at worst it might be a benign lump but I should go for a check up.
I had private medical care and only had to wait two days for an appointment instead of three to four weeks.
It's lucky that was the case because I found out I had a very aggressive form of cancer which would have got much, much worse had I waited.
'I knew I had cancer'
At the hospital I knew something was wrong because the nurse told me it definitely wasn't a cyst and I was sent for a biopsy.
It never crossed my mind that it could be cancer, I was convinced it was something else.
Two days later I went back for the results. I walked into the room and there was a Macmillan nurse I had met before. I knew as soon as I saw her I had breast cancer.
I felt complete and utter shock. You feel as if your life collapses around you. Like it has completely stopped.
I couldn't imagine there would ever be a time when I would come to terms with it.
Miss Stevenson said it was hard to find sufferers of a similar age
And then being told I would have to have chemotherapy, all I could think about was the hair loss.
I didn't deal with it very well, but luckily my boyfriend was a calming influence. I actually thought he would run a mile. But he didn't - neither did my friends.
The only way I can describe it is like being on a rollercoaster, which you have no idea how you are going to deal with.
I don't think I took it all in for a long time and I over-compensated, tried to get on with my life, more so than before and over did it.
I think I had a moment of clarity after my operation a few weeks later. I thought 'I haven't lost my breast, it doesn't look that bad and my scar isn't as big as I thought it would be'.
Side-effects of treatment
Then when chemo started I was back on the rollercoaster. I thought about losing my hair and began thinking my friends wouldn't want to be around me.
It was hard to control my emotions.
Being my age none of my friends had experienced anything like this, they could talk about older women, their mums or grandmas, but no-one my age.
I have a very active social life and I wanted someone to tell me if I could still go out with my friends, to pubs and clubs and parties. But there was no-one.
The worst thing was losing my hair. It sounds odd but I think if I had kept it I would have found it easier to cope with the other side-effects of chemo like the depression and infections.
I would lock myself in my room with the curtains closed and it wasn't until the end of chemo that I'd really learnt to cope.
I don't want this to come across as a negative story, like so much of the literature I have read, because my life has changed.
I've given up work and have gone travelling around the world with my boyfriend.
I am waiting for someone to turn around and say 'It's not coming back', but they can't just yet.
I have to have check-ups every three months and I am still on drugs which aim to stop the cancer coming back.
'Live your life'
But when you've been through an experience like this returning to the normal routine doesn't sit comfortably.
My friends didn't take much persuading to do the Moonwalk.
They've been through it all with me and I think they wanted to do something positive, although I don't think they've quite realised what they've taken on.
It's a way women can come together to do something without having to talk about what your friends, wives or relatives have gone through.
My first milestone will be two years clear, then five then 10, but I'm not even going to think about that until I get there.
It's going to be hard, but you've just got to live your life.
All funds raised by Walk the Walk's Playtex Moonwalk go to breast cancer research and care.