For most new mothers, it can be traumatic if their baby refuses to breastfeed - but in Sarah Boyle's case she believes it saved her life, reports the Daily Mail.
The 26-year-old call centre worker said her son Teddy, now 1, would become distressed and scream when she tried to feed him - but only when offered her right breast.
Concerned, she went to her GP and was referred to hospital for a scan and a biopsy. Two weeks later she was diagnosed with breast cancer.
She said: "Teddy is my hero - if it hadn't been for him I would never have suspected I had cancer.
My consultant told me breastfeeding helps a mother and baby bond. In my case it did more than that - it saved my life.
"Teddy could obviously taste the milk from my right breast was different from my left, so he rejected it."
She added: "My consultant said he'd never seen anything like it and was amazed. He told me it was very fortunate I chose to breastfeed otherwise my illness may not have been discovered."
Boyle said that when Teddy was born in February last year, he took to breastfeeding "fantastically".
Five months later, she noticed differences between her right and left breasts but her health care assistant told it nothing to be concerned about. A month later, however, Teddy stopped feeding from the right.
"If I offered him that breast he would completely freak out," she said. "He'd become extremely distressed and scream the house down."
Boyle is now planning a double mastectomy with immediate breast reconstruction surgery.
She had previously had a scare with a lump that turned out to be a benign cyst, so she returned to her GP and was told it was fine.
But the feeding problem continued. "Teddy just wasn't having it," she said. "I had no problems with my left breast but every time I tried with my right he would start screaming and get very upset. He wouldn't go near it."
When Teddy was 8 months old, Boyle returned to her GP and asked to be referred for a scan.
She said: "I felt as if Teddy was trying to tell me something. It was what you might call a mother's instinct."
In November last year, she had an ultrasound scan at Royal Stoke University Hospital that revealed a problem related to her cyst.
She then had a biopsy, and two weeks later was diagnosed with a form of the disease that is extremely rare in young women, known as grade 2 triple negative breast cancer.
"My mind went into meltdown.
"But I felt so proud of Teddy for bringing the problem to my attention. The cancer inside the cyst had been growing for three months - the exact same time Teddy stopped feeding from my breast."
The day she was diagnosed she was told to stop breastfeeding so she could start chemotherapy. She is halfway through the treatment.
She said: "It was sad losing my hair but I've been rocking lots of different wigs and am comfortable being bald around my loved ones now.
"I never imagined that I would be diagnosed with cancer so young but the hospital has been fantastic.
"I want other women to be aware of any lumps in their breasts and to always get them checked out."