The Wellwoman plan, developed by Unat Direct, covers specifically female cancers.
Unlike private medical insurance, which pays for medical treatment, the cash payable under this plan goes straight to the policy-holder.
"It's not designed to pay for hospital treatment because treatment of cancer on the NHS is excellent," said Unat Direct's marketing and development manager Janice Buffett.
"But if you are not able to work or your husband has to give up work or take a lot of time off, this provides some financial support so that you don't have to worry about money."
For an age-related monthly premium which starts at Pounds 3.95 for teachers under the age of 29 and rises to Pounds 13.95 for those aged 55-59, NASUWT members will receive Pounds 6,000 on diagnosis of a female cancer.
They will also be entitled to a monthly income of Pounds 500 for a year after diagnosis, a further Pounds 3,000 if they need surgery and Pounds 100 a day for up to 100 days while they are staying in hospital.
Paid during a very traumatic time in any woman's life, these benefits would undoubtedly ease financial worries and help reduce stress, as the insurance company claims. But before rushing out to sign up to the plan, NASUWT members will need to read the small print carefully.
If a teacher discovers that she has one of the female cancers within 90 days of taking out the plan, she will not be able to claim any benefits, though her premiums will be refunded. Nor will she be covered for a female cancer that her mother or any of her sisters have ever had.
With the Cancer Research Campaign estimating that genetic predisposition accounts for 4 per cent of breast cancers, this means that some of those most at risk of developing the disease will not be able to take advantage of the plan.
Even if they are not affected by these exclusions, some NASUWT women members may decide they are better off with a critical illness plan which will pay out a lump sum if they are diagnosed as suffering from any one of a list of diseases, not only a female cancer. While breast cancer kills more women in the UK than any other form of cancer (except in Scotland where more women die from lung cancer) heart disease is an even bigger killer.
According to the Office for National Statistics, 125,744 women died in 1995 as a result of diseases of the heart and other parts of the circulatory system - almost double the number who died from all malignant cancers.
But the extra cover provided by critical illness insurance is expensive. The Colonial insurance company gives a 5 per cent discount to NASUWT members taking out its critical illness plan. But Pounds 50,000 worth of cover would still cost a 30-year-old female non-smoker Pounds 20.81 a month, and premiums for older teachers would be even higher.