"Your son has Duchenne, there is nothing we can do. He is going to die, take him home, love him and give him a good life." These were the words that were delivered to me at my son Harrison's diagnosis. My first thoughts were – he's got what? How do you pronounce that? I've never heard of it?

That was just the beginning – almost no one I spoke to had heard of Duchenne muscular dystrophy (DMD) – yet it is one of the biggest genetic killers of children on the planet.

Two years later, the research charity we founded was looking for a way to start a conversation, raise awareness and increase the profile of the disease.

I had secured some space in the Evening Standard for a print advert to run in May 2013 and desperately wanted to maximise the potential of this opportunity.

We were lucky enough to be selected by creative agency AIS London as their chosen charity – taking the time to engage and work with a creative team made all the difference. If you can, I would recommend it to any charity.

Photograph: Harrison's Fund

During the creative process, the agency asked me to take them through Harrison's diagnosis, tap into the dark thoughts I had and be brutally honest about what I felt. We covered everything from start to finish – even so far as describing the corridor outside the consultants room we stood motionless in while Harrison ran around post-diagnosis. I quietly told them I wish my son had cancer.

I felt a cancer diagnosis would have more options, more of a chance, a chance to try something – a chance that those with DMD still don't have.

As soon as I said it they knew it would make an incredible advert, so the creative team went away and came up with a few ideas for the campaign. There was an idea about children writing their own will saying who they would like to leave their favourite toys to but the team kept coming back to those six words: "I wish my son had cancer."

A week later, with a look of trepidation the agency presented a single A3 sheet of paper with an image of a man staring straight at me with the words I wish my son had cancer. I instantly hated and loved it in equal measure. While the agency feared to run it, I didn't.

That is the thing about shock tactics in advertising, if you try to shock for the sake of it people see through it. If what you say shocks and is based on honesty and truth, it rises above the cookie-cutter adverts and distinguishes itself from other items on the page.

So far the campaign has been shared on a global scale, the cause is being talked about and becoming more known, and hopefully better funded. This is all I really wanted to happen.

Using shocking tactics in advertising does not come without its problems and I learnt it is vital to be prepared. It is guaranteed not everyone will agree with you, some people will miss the point and without a doubt you will get some hurtful comments.

When our campaign hit social media, our Facebook page lit up with comments from the UK and the US. I spent 36 hours replying to them all individually – it felt like my responsibility to do that. The majority of criticism I received was centred on the use of the word cancer as a catch all for the disease. We were criticised for amalgamating all cancers in one sentence rather than being sensitive to individuals with specific, aggressive cancers that can have very low survival rates.

Parents, understandably, reacted very emotionally. "You deserve to have your children taken away from you," and "you don't deserve to be a father" were just some of the comments I received.

I'm often asked if I regret placing the advert and whether I would do it again. I would. In my opinion, being blatant is one of the only ways small charities can gain the same traction and voice that larger organisations do.

The I wish my son had cancer campaign has gone on to win over 30 international advertising, press and copywriting awards and is by far the most successful piece of work ever produced by AIS London. Not bad for a small black and white press ad.

Alex Smith is the founder of Harrison's Fund.

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