Queensland research has found the incidence of keratoacanthoma (KA) is much higher than previously reported.
The research, from QIMR Berghofer’s QSkin study cohort, found 596 of 40,438 participants developed 776 keratoacanthomas during a median follow-up of three years from baseline.
This equated to an incidence of 409 affected individuals per 100,000 person-years.
“The incidence of KA in our study is 2.5 times higher than that documented in a 1979 study conducted in 3 Australian pathology departments, which found an incidence of approximately 150 cases per 100,000,” the study said.
However the incidence of KA was about a third of the incidence of cSCC – 1,270 individuals per 100,000 person-years – reported from the same Queensland cohort.
About 5,000 Queensland adults develop keratoacanthomas each year.
The study, published in JAMA Dermatology, showed keratoacanthoma has similar risk factors to other skin cancers and that many factors such as sun exposure, smoking and alcohol consumption were modifiable.
It found older age (HR 6.38), male gender (HR 1.56), fair skin (HR 3.42), inability to tan (HR 1.69), previous excision of a skin cancer (HR 6.28), current smoking (HR 2.02) and high alcohol use (HR 1.42) were significant risk factors.
As well, participants with many freckles compared with no freckles at age 21 years had a higher likelihood of developing KA (HR, 1.44) as did those who reported 11 or more sunburns compared with those who reported no sunburns before age 10 years (HR, 1.35).
Other variables such as a tendency to sunburn, eye color, hair color, and self-reported sunburns after age 10 years showed some association with KA after adjustment for age and sex, but were not statistically significant after final adjustment.
The researchers said KAs can pose a diagnostic dilemma to doctors because they may look similar to more aggressive SCCs.
First author Dr Magdalena Claeson, a Swedish dermatologist and researcher in QIMR Berghofer’s Cancer Control Group, told the limbic there was still some debate around the world about the true nature of KAs.
“Although we have known this tumour since the 1890’s we still cannot say confidently if they are dangerous to the patient or not.”
“We know that most, usually, are not dangerous but there are a couple of reports in the literature that say they can metastasise. That’s why it is considered a form of SCC and most commonly removed surgically.”
She said there were also reports of the tumour resolving spontaneously but keratocanthomas had not been well researched to date.
“Unfortunately, this study doesn’t give us any more clues as to what is a keratoacanthoma and what is an SCC just from looking at it clinically.”
“If we had a test that could tell that this is a benign form of SCC rather than a more aggressive SCC that can metastasise, that would be great. But we don’t have that so we have to surgically remove it for a diagnosis.”
She said the study has at least provided some good quality information that the risk factors for KA are similar to those for other skin cancers.
“Other studies have suggested that sun exposure, older age, male sex and fair skin were all risk factors for keratoacanthoma but this is the first time that we’ve had better evidence.”
“That’s very important for the public to know that ‘slip, slop, slap’ is useful also for this tumour. And smoking and alcohol are kind of new risk factors in this area of skin cancer.”
“With SCCs for example, smoking has been suggested before in other studies but it is not one of the typical risk factors that people would associate with skin cancer.”