Linda Tizzard's decision to give blood helped to save her life.
A routine blood test taken at the start of the session showed she had a problem and that she should contact her GP.
Further checks by consultants at Worthing Hospital revealed she was suffering from myeloma, a cancer of the bone marrow.
Mrs Tizzard was stunned at the news.
She said: "I hadn't been feeling ill at all so it was a complete shock.
"They got me into hospital very quickly and I am just so relieved they caught it then.
"Otherwise, the only time I would have known something was wrong would have been when I started feeling ill or showing symptoms.
"Going to give blood that day made all the difference."
Mrs Tizzard, who was 42 when she was diagnosed, went though chemotherapy sessions while relatives were checked to see if they were a suitable donor for a bone marrow transplant.
No suitable match was found so specialists at Charing Cross Hospital, London, decided to do a stem cell transplant.
Stem cells are blood cells at their earliest stage of development.
Mrs Tizzard, from Rustington, had some of hers taken from her bone marrow and then had chemotherapy and radiotherapy to destroy white and red cells, including the cancer carriers.
The stem cells were then put back to regenerate.
The intensive treatment forced Mrs Tizzard to give up her job as a home care assistant and put extra pressure on her husband Dave.
She said: "It was a hard time for everybody. We had four children to worry about and it was very stressful."
Shortly before Mrs Tizzard went for her treatment, the family were put in touch with the Friendship Group.
The group was established by Worthing Hospital lung care specialist nurse Jenny Stanley and ex-cancer patients Hilary Parley and Elaine Stevens.
It offers support to people and their families going through cancer by getting former sufferers to provide the help.
Mrs Tizzard said: "A man came to see us and stayed for about two hours telling us about his experiences and giving us tips on how to get through it all.
"It was very comforting and gave us an extra boost. Just knowing we weren't alone made all the difference."
When Mrs Tizzard came out of hospital it took about six months for her to build up her strength and get back to work.
She said: "The first sets of chemotherapy were not too bad but the treatment for the stem cells was very difficult and left me feeling very ill."
Now 50, she has been in remission for several years and is living life to the full.
She and her husband help out on the committee of the Friendship Group, offering their own advice and support.
The group, which originally helped people with blood cancers, is expanding to include people with all types of cancers.
Mrs Tizzard said: "We don't claim to be major health experts but because we have been through the experience we can understand what people are going through."
The group also looks at alternative treatments, including aromatherapy and yoga, and holds practical sessions such as inviting a wig maker to talk to patients who have lost their hair through chemotherapy.
Regular newsletters include contributions from patients, nurses and members and there are fund-raising events such as sponsored walks, stalls at fetes, raffles and coffee mornings.
The group is supported by James Heasman, cancer services manager at Worthing Hospital.
It is open to people living in the catchment area for Worthing Hospital and Southlands Hospital in Shoreham.
This includes Southwick, Littlehampton, Lancing and Henfield.
For more details, call Mrs Tizzard on 01903 770547 or Mr Heasman on 01903 205111 ext 5805.
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