I was 27 when I found out I had cancer. I had just moved out of home. Pathetic, I know, but rents were high and I was suffering from crippling laziness. I was painting houses and doing deliveries. I was just floating along. My mother sat me down one day and told me that if acting was what I really wanted to do, I needed to move out, get a job and start saving to go to London.

As a kid, I was always trying to break the silence with a laugh – always looking for attention. Around the time of my Leaving Cert, I decided I wanted to be an actor. I had a meeting with the Lisa Richards Agency. They said, "You should really think about comedy. Your letter was funny. That's why you're here. It's not because of your passport-photo headshot."

I moved in with two girls I knew. It was like a sexless bigamist marriage with passive-aggressive cleaning. I got myself a decent agent. I got an audition for a part in Boardwalk Empire. I nearly had it too. There's a lot of nearlys in this story. I started to get callbacks. There was a sense of momentum.

To celebrate, I was playing with myself in the shower. I found a lump. I knew what to look out for, so once a month I would check. I went to the doctor straight away. She said it would take three months to get a scan on the public system because it wasn’t serious. I told her I wanted it done tomorrow; I’d pay for it myself. When I went for the scan the next morning, the man doing the ultrasound said, “These things are usually nothing.” I watched him watching the screen. I said, “Don’t reveal the sex of my balls; I want it to be a surprise.” He was silent. “There’s definitely something we need to be concerned about,” he said. He referred me to a urologist. I drove home, blubbing in the car.

‘Get rid of the ball’

The urologist talked in a slow, neutral way, like Obama when he talks about war but doesn’t want to alarm anyone. “The likelihood is you’ll be fine.” He wanted to do a biopsy first. I said, “No, get rid of the ball. It’s the smaller one anyway. The weaker of the two.”

I went back three weeks later for the histology results. His office was really busy because he’s the big prostate guy. I was always the youngest person in the waiting room. He said, “What we found was quite aggressive. We have a question that we need to answer. Do you want it all removed or do you want to monitor it?”

I decided to have the testicle removed. I’d get a prosthesis. I didn’t want to be reminded of it every time I looked down. I was single at the time and I didn’t want to always have to have a pre-coitus cancer conversation.

When you have cancer, people say mad things to you. A friend said, “Well, in fairness, you did smoke.” My dad’s friend said, “If it’s gonna kill you, at least you know what got you.”

I’d lie awake at night thinking, why did I want to be an actor? Why didn’t I do something normal so I wouldn’t have to be worried about money on top of this?

It’s a bang-up job down there, however. It feels like a Persil liquid tab. It looks 10 years younger than the other one.

A call from Brendan Gleeson

While I was recovering, my dad met Brendan Gleeson and asked him would he ring me with a bit of acting advice. On the phone Gleeson told me, “You need to not want it too much. Have something going on the side, so when you go into the audition, you’re not relying on the money.”

When I told him I was sick, he said, "Your dad didn't tell me." I thought he had called me in a sort of Jim'll Fix It way.

When I was all healed, I got to work. I got a sales job and a restaurant job. I had an audition for a Mace ad. Because I didn’t care, I got the part. After the Mace ad, I had an audition for a Lotto ad. “It could be you.” I got that too.

An old friend told me there was a room available in his house in London, so I went. There are so many more opportunities there.

Des Bishop once told me that with acting, you’re waiting for the phone to ring, but with stand-up, you write your own stuff and make your own calls. I had tried stand-up before, and it went really badly. I got heckled. I got in a fight afterwards. But losing the ball made me realise stand-up wasn’t something to fear. The confidence comes from doing it again and again.

When my savings ran out, I got another job in a restaurant. I ended up serving Jimmy Carr one day. I told him I was doing the rookie circuit where everyone in the audience is another stand-up. He said, "Get yourself to Edinburgh. Save. Do a free show." I booked in the next day. I didn't know what I was doing. I was handing out my own flyers, and they were overflowing from the nearest bin. I had audiences of four and five. Luckily, I got a good review from The Skinny. It opened doors to paid gigs in London.

Things were moving in the right direction. I got an audition for a short film, Scratch. I got paid gigs in the International Bar in Dublin. It took leaving Ireland to be able to do that. People leave to get back in. In acting, the talent is often secondary to getting into the room. Comedy is more of a meritocracy.

Last Christmas, I was getting a routine check-up and they found a problem in my good ball. There was another tumour. The oncologist told me I should freeze some of my little men. This time, though, the doctor said that he wanted to go in and take out only the tumour. I was back in my parents’ house again, waiting. Six weeks later, I found out it was benign.

Do I feel lucky? Well, I'd prefer to be the winning the lottery kind of lucky. But I knew I needed to work harder. A comedy agent offered me a gig in a small place in Leicester Square. I opened a show for Romesh Ranganthan. Scratch was shown at the Tribeca Film Festival in New York. I got to meet Robert de Niro. That made me feel lucky.

I don't think the cancer changed my life that much. For a moment, you appreciate the important things, and then you get on with thinking about what you're going to watch on TV at night. Writing a show about it worried me because I didn't want to be "the balls guy". But I've always talked about it. It made me feel better to share it with people. I wrote Nutjob, which is running at the Edinburgh Fringe this year. I went through something a lot of guys would be afraid of, but it isn't the worst thing. It made me confront my own mortality. For the first time, I thought, I can't have children if I'm struggling like this, so I need to keep working at it.

I made things more difficult

It’s on my mind that I’m not making use of the opportunities and privileges I had growing up. I went to a private school. I went to university. I’ve made things more difficult for myself and for my parents. A lot of their friends’ children are doing things that are more traditional. I bumped into a guy I know from home. “Thank God for you,” he said. “You’re the example my mam always used as someone I don’t want to end up like.”

I went to a school reunion last year. I was really apprehensive about it. I was 30 and I’d been in London for a year. I didn’t want to go because I’m nowhere near where I’d like to be. Dad said, “Don’t worry about it. It’s a 10-year reunion. Most people have no idea after 10 years what they’re doing. If you still feel like this at the 20-year reunion, then don’t go.”

I went, and it was a relief to discover that lots of people were unhappy. One or two guys were particularly successful, but almost everyone else was climbing a ladder of some sort and not too sure if it was the right one. A lot of guys had gone travelling at 25 and come back to nothing. People were coming up to me saying, “It’s great to see you doing so well.” The only time they had seen me since school was on the Lotto ad. One said, “It’s great to see someone I know doing exactly what they want to do.”

Nutjob is at the Edinburgh Fringe Festival until August 25. conordrum.com, edfringe.com