Mollie Mulheron, 24, had recently returned from the Galapagos Islands before she began suffering trouble breathing and swallowing.
She returned to the UK on February 4, after nine months abroad, and within 48 hours began vomiting and collapsed in a Booths supermarket in North Yorkshire.
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Miss Mulheron was taken to hospital, where doctors carried out tests.
Medics found a 15cm tumour over her heart and lung and diagnosed her with stage four non-Hodgkin lymphoma (NHL).
'I just cried and screamed and screamed - it was out of nowhere, I knew something was wrong but I didn't think it was that wrong,' Miss Mulheron said.
Due to the aggressiveness of her cancer, Miss Mulheron was unable to undergo cryopreservation - before she started chemo on February 21.
Doctors instead gave her an injection to put her in a temporary early menopause in the hope that once chemo was completed, she could conceive.
She said this was 'the worst part for me as I always wanted to be a mum'.
Miss Mulheron had flown to the Galapagos Islands to pursue her dream of travelling.
However, while out there she began to experience strange symptoms, including rashes.
'I've been fit and healthy my whole life, I've always been completely fine - I don't know what has caused this, I'm healthy and young, three weeks ago I was in Galapagos living my best life', she added.
Doctors told Miss Mulheron they are hopeful they can treat the cancer as there are many options due to her being young, fit and healthy.
Statistics suggest stage four NHL has a five-year survival rate of around 64 per cent.