Midland MP Debra Shipley is to stand down after revealing she has cancer.
The Labour MP for Stourbridge has been receiving treatment for six weeks and will undergo an operation next month.
Her husband, Simon Molesworth, died of bone marrow cancer last year after battling the illness for seven years.
The couple were married in 2002 and have one daughter.
Her Black Country constituency of Stourbridge is the most marginal constituency held by Labour in the West Midlands.
Conservatives would need a swing of 1.6 per cent to overturn a majority of 3,812.
Ms Shipley said: "For the last six weeks I have been in and out of hospital and I have been diagnosed as suffering from cancer. On April 4 I will undergo a double mastectomy."
She added: "My husband was diagnosed with cancer in 1998 and died last year.
Throughout his illness I have been grateful for the support and understanding of my constituents and neighbours in Stourbridge and colleagues in Westminster."
Ms Shipley, aged 47, was educated at Kidderminster High School, Worcestershire, and worked as a lecturer before entering Parliament in 1997.
The highlight of her political career was introducing the Protection of Children Act, which created an official list of people who unfit to work with children and required organisations involved in childcare to vet potential employees against the list.
It was a rare example of a Bill introduced by a backbencher successfully becoming law.
She has also led a longrunning campaign to improve school dinners, and attempted to introduce legislation banning junk food in schools.
Ms Shipley voted against the war in Iraq, and was a low-key critic of other Government policies including Foundation Hospitals.
She said: "I would like to put on record how much I have
enjoyed the privilege of representing Stourbridge in Parliament.
"I am proud to have been responsible for the Protection of Children Act and the Children's Food Bill, both of which I sincerely hope will have a lasting effect on the health and well-being of all our children."
She added: "I will miss being MP for Stourbridge, but with my health failing so seriously I know that standing down is the right thing to do at this time.
"Should constituents wish to contact me they can do so until the end of May by writing to my constituency office at 20-22 Hagley Road, Stourbridge DY8 1QQ."
Last night Westminster colleagues paid tribute to her work as an MP.
In a statement issued by the Labour Party, Bob Ainsworth (Lab Coventry North East), the Deputy Chief Whip in the House of Commons, said: "We fully understand Debra's decision. Her departure will be a loss to the Labour Party and I know that people in the Party and in her constituency will be very saddened.
"Debra has been an assiduous constituency MP, always on the side of her constituents and has been a pleasure to work with.
"We are thinking of Debra and her daughter at this difficult time."