By Jane Elliott
Health reporter, BBC News
Elisa is now a successful musician
Each year 46,000 people are diagnosed with breast cancer - only four of these are under 20.
So when 19-year-old student Elisa Caleb went to her doctor with a lump everyone felt quite confident it would be benign.
Elisa was told the results were clear.
But she says they were unclear. And medics were so confident that she was too young to have the condition, they did not tell her of the uncertainty, or order any further tests.
It was only when she decided herself to have the troublesome lump removed a year later, that she was told she had an aggressive cancer.
It needed to be removed immediately and followed by chemotherapy and radiotherapy.
"I was completely stunned because every day the lump had been in my thoughts and I'd thought it was nothing to worry about," said Elisa, now 29.
"It was really, really numbing because I had been living with this illusion that it was OK, but it wasn't.
"I think the reason they didn't find it in the first place was just because they assumed I was too young."
Elisa said she is very lucky indeed to be alive today as she had only decided to have the lump removed because it had become too uncomfortable.
It had grown from the size of a marble to a golf ball and was protruding through her skin.
"It was a really sobering thought," she said.
"It is pretty scary to think I am only here because I opted to have it removed.
Elisa likes to spend time with her family
"It was quite an aggressive cancer when they took it out. It could have been a lot worse."
Jackie Harris, clinical nurse specialist at Breast Cancer Care, agreed that Elisa was very young to have the cancer.
"It is extremely rare for women in their teens to be diagnosed with breast cancer," she said.
But she said that should not stop younger people checking their breasts.
"Early detection of breast cancer can lead to simpler and more effective treatment, so it's important that women of all ages are breast aware throughout their lives - getting to know how their breasts look and feel normally so they can report any unusual changes to their GP immediately."
Elisa, who now sings jazz for a living, said her life has completely changed since her diagnosis.
"My priorities have changed," she said.
"I am not so anxious about things and if things don't work out it doesn't bother me as much.
"I have a daughter and spending time with her and my family is important.
"You don't know how long you have."
Elisa took tamoxifen for five years and still has regular check-ups.
"At the time I did not feel angry, I was just relieved it was caught.
"But looking back it is really silly not to do a thorough test. If the doctors have done a test and it's not clear, they should do another one.
"I do wonder how many other people are in the same situation."
Her album Carry Me Home is out on May 24