Cancer Research UK said each year, the most serious type of skin cancer, malignant melanoma, kills 1,300 men and 900 women, a gap expected to widen.A reason could be men delaying seeking help, but biology may also play a part.Prof Julia Newton-Bishop, a Cancer Research UK dermatologist, suspects women have stronger immune systems.German researchers have already identified a gene that appears to make men, but not women, more susceptible to melanoma.Prof Newton-Bishop, from the University of Leeds, said: "Research has suggested the difference between the sexes could be in part because men are more likely to be diagnosed when melanoma is at a more advanced stage."But there also seem to be strong biological reasons behind the differences, and we're working on research to better understand why men and women's bodies deal with their melanomas in different ways."Stage for stage, men do less well with this cancer so there's something very important that this is telling us about how the body deals it."We think it is something to do with the immune system rather than hormones because pre- and post-menopausal fare the same."Delayed diagnosisAnother concern is late diagnosis.Men, unlike women, more often develop the cancer on their back rather than arms and legs which may make it more difficult for them to spot."Asking your partner to check your back is a good idea," said Prof Newton-Bishop.Malignant melanoma death rates have been increasing in the UK since the early 1970s, largely because more people are developing the disease.Male incidence rates are now more than five times higher than they were 30 years ago - rising from 2.7 per 100,000 to 17.2 per 100,000.Getting too much sun and using sun beds increases the risk of this largely preventable disease.To protect their skin, people are advised to use a sunscreen with at least SPF15 and good UVA protection - the higher the star rating, the better - and to be aware of changes in the skin, including a new growth or a spot or mole that itches, hurts, bleeds or will not heal.Treatment is more likely to be successful if melanoma is spotted early.