Cases of the deadliest form of skin cancer are on the rise among young women, but not young men, according to a study published Thursday in the Journal of Investigative Dermatology.

Analyzing government data on Caucasian men and women ages 15 to 39, Mark Purdue and his colleagues at the National Cancer Institute found that, between 1980 and 2004, annual cases of melanoma among young women increased by 50 percent from 9.4 cases per 100,000 women to 13.9 cases per 100,000 women.

Researchers also found a greater increase in young women having thicker and metastatic melanomas in which the cancer spreads to other areas of the body during that time period.

The incidence of melanoma among young men did not change over this time period, the authors noted in a press release.

Melanoma is the deadliest form of skin cancer. The condition usually begins with a mole that's changed shape or with the appearance of a new mole.

The National Cancer Institute estimates there will be 62,480 new cases of melanoma and 8,420 deaths in 2008.

It's unclear why the incidence of melanoma among women is increasing, the study's authors noted. Additional research is needed to investigate whether young women are increasing the amount of recreational sun exposure they get or use of tanning beds, both of which are risk factors for melanoma, they added.

Click here for more on this study from the Journal of Investigative Dermatology. (Subscription required).