Vicky Veness, from Cheltenham, does not smoke, eats healthily and is very active and as a result looks very healthy.
So when she went to see her doctor because she was feeling unwell, they initially brushed it off as asthma.
However, 18 months later she was told that it was actually cancer.
She now wants others to hear her story and urges people to question what they are told.
She wrote on Facebook: ‘Just a warning that this post may be upsetting to read.
‘This photo was taken a few hours before I was diagnosed with stage 4 lung cancer. I’m 30 years old, a personal trainer, runner, non smoker and healthy eater.
‘When you have cancer you won’t necessarily look ill on the outside. The symptoms might be much more subtle and only show themselves occasionally.
‘Unfortunately my symptoms were brushed off as asthma by many general practitioners.
‘The moral of the story is this, if you feel unwell for whatever reason, it doesn’t matter how silly you might think it might be, see your doctor, question everything and keep going back until you get the answers you need.
‘This has been the most emotionally and physically challenging week of my life, but now it’s time to fight this!’