MONDAY, Dec. 18 (HealthDay News) -- Potentially fatal skin cancers called melanomas are more likely to grow fast when they're thicker, symmetrical, elevated, have regular borders or produce symptoms, a new Australian study found.

"Rapidly growing melanomas can potentially kill in a matter of weeks," said lead researcher Dr. Wendy Liu, of the Peter MacCallum Cancer Center, in East Melbourne.

"They can occur in anyone, not necessarily those with large numbers of moles and freckles. In fact, they more often occur in those without large numbers of moles and freckles and elderly men. They are more often red, rather than brown and black, symmetrical, elevated and symptomatic," Liu added.

In the study, Liu's team investigated the growth rate of melanoma in 404 patients with invasive melanoma. Patients had their skin examined, and data about the moles were collected. In addition, patients were interviewed as soon as possible after diagnosis.

Patients and their families were asked to recall when they first noticed a spot on their skin from which the melanoma later developed, and when they noticed the mole had changed or become suspicious.

The researchers collected data on demographics, skin cancer risk factors, the characteristics of the tumor and who first detected the cancer -- the patient, a family member or friend, or a physician.

Using this information and the thickness of the tumor when it was removed, Liu's group was able to estimate its rate of growth.

The researchers found that about one-third of all the melanomas grew less than 0.1 millimeters per month, another one-third grew between 0.1 millimeter and 0.49 millimeters per month, and one-third grew 0.5 millimeters or more per month.

Rapid tumor growth was associated with tumor thickness, ulceration (formation of a break or sore on the skin), amelanosis (lack of pigment in the tumor), regular borders, elevation and symptoms.

Moreover, faster-growing melanomas were more often found in people 70 and older, in men, and in those with fewer moles and freckles, the researchers reported.

Factors not associated with the rate of growth were the number of atypical moles or age spots or liver spots; a history of sun damage or blistering sunburns; skin type; eye color; family or personal history of melanoma; and current or childhood sun exposure.

"Rapidly growing melanomas no longer fit the classical description of melanomas," Liu said. "We need to promote the awareness of this less common but more aggressive form of melanomas among the health professionals and the general public."

But Liu cautioned that "any rapidly growing skin lesion, regardless of its morphology and perceived risk factors for melanoma, deserves prompt medical assessment."

The study findings are published in the December issue of the Archives of Dermatology.

One expert noted that most cancers have rapidly growing forms.

"This is not a surprising finding," said Dr. Vijay Trisal, an assistant professor of surgical oncology at the City of Hope Cancer Center, in Duarte, Calif. "You can extrapolate these findings to any tumors in the body."

Tumors that are fast-growing are more aggressive, and can divide faster and invade vessels and organs more quickly, Trisal said.

Trisal added, however, that asking patients about the growth of their melanoma is not an accurate basis for estimating the speed of the cancer's growth. "It is very subjective," he said. "It also depends on where the lesion is. If it's on the back, it might not be noticed for a long time."

"Tumors that grow fast are particularly worrisome, especially if you have no chemotherapy for them," Trisal said. "For melanoma, we have no chemotherapy, and the faster they grow, the worse they are, because that means that the tumor has the ability to get into the blood vessels and lymph nodes faster."

People should get medical attention as soon as they notice a melanoma, Trisal said.

"You can't just sit there and watch a melanoma grow and say, 'Fine, it hasn't grown in two months, so it is not that aggressive,' because you want to get on top of it sooner," Trisal added.

More information

The U.S. National Cancer Institute can tell you more about melanoma.