She faced a gruelling operation and nearly died after her lungs collapsed while she was on the operating table.
But the 64-year-old knows she is one of the lucky ones – because doctors declared her cancer free in March.
However, despite her reprieve from one of Scotland's biggest killers, the great-grandmother is still battling her cigarette addiction.
She is a week into her latest attempt to quit – and has promised it will be her last.
This time she is doing it for her four grandchildren and two great grandchildren, especially granddaughter Courtney, 13, who has raised cash for Cancer Research UK.
Mrs Brocas, from Airdrie, said: "Since my surgery, every day is a bonus. I have a second chance at life. I am very lucky. I want to live at least another 10 years – I want to see my grandchildren and great grandchildren grow up."
Courtney, who lives in the same street, is her biggest supporter.
The St Margaret's High pupil remembers being told her gran had cancer. She said: "It was like somebody took a bit out of my heart."
She decided to raise money for Cancer Research with pal Lauren McLean, 11, from Airdrie Academy.
The pair got family and friends to join them in walking eight times around Drumpellier Loch in Coatbridge to gather £300. The teenagers were give special medals by Cancer Research UK for their efforts.
Mrs Brocas, who has been married to Graham, 64, a security officer for 46 years, had suffered none of the symptoms of lung cancer. These include coughing, chest pain, weigh loss and breathing difficulties, until she became ill in November last year.
She said: "On a Sunday night, after my dinner. I felt sick. I went to the toilet – but it was not vomit that came up, it was blood. My husband said, 'You get to the doctor's tomorrow'.
She went to her GP, who sent her for an X-Ray at Monklands General Hospital.
Mrs Brocas said: "The girl said, 'There is something here I don't like – you'll need more tests.' The first thing I thought was, 'It's cancer'."
She had scans and a tube put through her nose and down into her chest, as well as a biopsy to take tissue from her lung.
Then, one day in January, she got the devastating diagnosis.
She said: "They said. 'You have a cancerous tumour.' It broke my heart. I was dumbstruck."
Luckily, the tumour was a rare operable case, and she had it removed at the Golden Jubilee Hospital, Clydebank, on February 22.
The tumour was the size of a two pence piece. However, her lungs collapsed during the surgery and she ended up in the high dependency unit for three days.
However, she has made a full recovery and did not need to have gruelling chemotherapy or radiotherapy – or worse.
Half of all lung cancer patients are dead within four months of diagnosis.
But Mrs Brocas is still fighting her smoking addiction.
She started smoking when she was 24 – and pregnant – before the risks were known.
She said: "My neighbour said, 'Here, take it'. It was a No 6 and I liked it. But I wish I had never started.
"If I could say anything to any young people today it would be: 'Do not start, it's very easy to do. But it's 10 times harder to quit'."
Mrs Brocas was spending up to £20 a day – £140 a week – on cigarettes but she stopped before her operation.
She was smoke-free for 68 days – before starting again in June.
"I said I would like a fag, just one. But one leads to 10, 10 leads to 20 – say no more," she said.
However, last week Irene promised to try again with the help of the drug Champix, which reduces cravings.
She also has a tin to save the money she would have spent on cigarettes so it can go towards a holiday in Benidorm.
This time she is thinking of spending as much time as possible with other grandchildren Lisa, 20, Andrew, 14, and Callum, 6, as well as great grandchildren Kayden, 3 and Kiera, 3, who are Lisa's kids.
She said: "My family is the most important thing to me, especially now I have a second chance with them."
Mrs Brocas said of the Evening Times campaign: "I think it is the best thing since sliced bread. If I can get one young person not to start that is one person who going to live longer."
Vicky Crichton, Cancer Research UK's public affairs manager, said: "It is great the Evening Times is working with its readers to raise awareness of the dangers of tobacco.
"Tobacco is highly addictive and kills half of its long term users. Stopping smoking is the single biggest preventable cause of cancer.
"We know giving up can be tough, but smokers are more likely to quit successfully with support from NHS smoking cessation services."
LUNG cancer is the biggest cancer killer of women, and death rates have risen 11% over the past decade. A total of 90% of lung cancer cases are caused by smoking. As part of the Evening Times Clear The Air campaign, Sarah Swain meets a woman whose lifelong habit saw her suffer the deadly disease
OUR Clear The Air campaign – run in conjunction with NHS Greater Glasgow and Clyde and NHS Lanarkshire – aims to highlight the risks of Scotland's biggest killer and help you quit smoking for good.
Every day in Scotland, 36 smokers die from horrific illnesses, such as lung or mouth cancer, stroke or heart disease.
Then there is the harm caused to others by second-hand smoke, not to mention the spiralling cost.
For help to stop smoking see our website at www.eveningtimes.co.uk/cleartheair or call Smokeline on 0800 848484.
Find us on Facebook by visiting on.fb.me/clearair and Twitter bit.ly/etclearair.
We are also looking for your stories. Call reporter Sarah Swain on 0141 302 6532 or send an e-mail to: firstname.lastname@example.org