I take my T-shirt and bra off and lie on the bed. I close my eyes to concentrate. I have to do that otherwise I get distracted by the spiderweb on the ceiling. The minute I start thinking about what a terrible housekeeper I am, will be the moment I leap up to wield a broom. For about two minutes. And then neither clean the house nor check my breasts.

So, I imagine that I am about to explore the globe. Although it's a long time since my breasts were anywhere near as perky as a globe. Then begins the march of the fingers. My second and third fingers poke and prod, looking for something that seems unusual. Occasionally I'll call on my thumb to really interrogate what lies beneath.

At my age, my breasts are somewhat explored territory. Large, droopy and filled with squeezy, squashy bits. As I do this, I wonder, does that feel the way it has always felt? I swear the nipple area is the worst. Is that really a new lumpy bit or is it just that I can no longer remember what it felt like a month ago? How long has it felt like that? What did it feel like in the decades before breastfeeding? It's even stranger now I've lost weight.

Then I get up, stand in front of the mirror and take a long, hard look. Raise one hand over my head and then the other. Turn sideways and have another critical look. Hmmm, more uneven than before? That would take talent.

What's even worse is that when I leave it for longer than a month – sometimes as long as four months – each interaction with the strange texture of middle-aged breasts sends me into a slight frisson of anxiety. Still, this is my front yard and I've been looking at it and feeling it for nearly half a century.

Every breast-cancer prevention site in cyberspace will tell you that in order to get an early diagnosis, you need to be aware of the normal look and the normal feel of your breasts.

In my case, I hyperventilate as the date of my biannual mammogram approaches – and am very relaxed, if somewhat flattened, afterwards.

Kirsty Brook was having one of those breast-check moments, three years ago. She was very pregnant, lying on her bed and feeling her tender, swollen breasts. Her fingers encountered a lump close to her armpit. She played with it for a little while. Was it different?

Just the Christmas before, a friend had bought Brook a breast self-check kit. At the time, she thought it was funny, a strange gift.

"It felt solid but not painful and it felt a little bit tingly," she says now. It was as if a little vague prickly feeling led her straight to the spot. Straight to the lump. But she didn't panic and waited until her next routine obstetric check.

Yes, it was cancer, but everyone remained calm. Brook, her husband Ian, son Finlay and the medical staff negotiated a suitable date for an induction but Willem decided to arrive early, waters breaking just after his mum had made a plaster cast of her belly and boobs. She was still cleaning the bathroom.

Ten days later, Brook had the first of three operations, which would result in a complete mastectomy of her left breast.

"They told me I would have to wean but secretly I didn't," she says, "I just breastfed with one boob."

She describes it as providing Willem with an entree.

There was no breast cancer in her family anywhere.

Brook had chemotherapy and radiotherapy until June 2010. There is absolutely no sign of the cancer returning.

She says she was pretty lucky. Although she was young to experience breast cancer – she was just 35 when she found the lump – her medical team took her seriously. Brook says that occasionally young women who find lumps have trouble getting anyone to take their concerns seriously. But she also thinks it is important for young women to recognise how important it is to be familiar with the look and feel of their breasts.

This Mother's Day, Brook will run in the Women in Super Mother's Day Classic, a fundraiser for breast cancer research, for the fourth time.

The first time, in mid-2010, she was still having treatment and, as she says, was as bald as a badger. Brook walked with Ian, Finlay, and Willem in the pram. She does it to raise awareness but she also does it to celebrate. It's her way of reclaiming Mother's Day.

Registrations are open now and, if you register early, you might even win a prize.

Brook says the best prize for her would be an answer to the puzzle of breast cancer.

"Life would be a little bit sweeter if I knew there was a cure," she says.

Help Brook celebrate and raise money for research. Run with her.