Lichen planus linked to more mouth and genital cancers, but 20-year oral cavity cancer risk stayed near 1%

Lichen planus often announces itself as an itch: a patch of small purplish bumps on a wrist or shin, or white lacy streaks inside the cheek. For decades, people diagnosed with it have asked the same follow-up question, whether it can turn into cancer, and the honest answer has been a hedged yes for the mouth and a shrug for everywhere else.

A Danish study of 35,845 patients now puts numbers on that answer for every part of the body the condition reaches. Researchers at the Danish Cancer Institute in Copenhagen, led by Cecilia Egede Medianfar with Susanne Kjær as senior author, linked national records of lichen planus to the Danish Cancer Register. Their retrospective cohort study using national records was published on October 14 in JAMA Dermatology. In women, lip, mouth and tongue cancers turned up six to 7.5 times more often than in the general population, and genital cancers more than twice as often, with each excess concentrated where the lichen planus had appeared. Over 20 years, though, about 1 in 100 patients developed cancer of the inner mouth, with tongue and lip cancers counted separately.

What is lichen planus?

Lichen planus is a chronic inflammatory disorder that usually begins in middle age. A review in The Scientific World Journal describes it as a T-cell mediated immunologic disease: the immune system’s T cells attack the body’s own tissue, for reasons nobody has pinned down. On the skin it tends to show up as small, itchy, purplish, flat-topped bumps, often on the inner wrists and lower legs. It can also involve the mucous membranes, the moist lining of the mouth, genitals, gullet and other passages.

The condition is more prevalent in women, and its forms differ in how they behave. Skin lesions typically resolve within 6 months to a year, while erosive oral lichen planus, which leaves raw, broken areas inside the mouth, may have a more chronic pattern. A 2021 overview of earlier reviews tied cancer most closely to thinned or eroded patches and to the location on the tongue.

Why the cancer question was still open

Doctors have suspected a link for a long time, at least in the mouth. A consensus group convened by the World Health Organization’s Collaborating Centre for Oral Cancer lists oral lichen planus among the oral potentially malignant disorders, a set of conditions that raise the chance of cancer of the lip or mouth. That overview, which pooled seven systematic reviews, put the share of people with oral lichen planus who later got oral cancer at between 0.44% and 2.28%. The same overview judged most of those reviews to be of critically low methodological quality, because many rested on small clinic series followed for uneven lengths of time.

Outside the mouth the evidence was thinner. A 2022 review of vulvar conditions went only as far as saying that an increased risk of developing vulvar cancer has been suggested for lichen planus. A 2026 meta-analysis of skin and genital lichen planus, pooling 15,829 patients, found cancer in about 1% overall, with a pooled rate of 2% in vulvar disease and close to none on the skin.

The Danish authors open their paper by saying that the association with cancer, particularly by anatomical site, is not well established. That last point is where their study adds most. Denmark’s pathology register records where a biopsy came from, so the team could ask whether cancer followed the lichen planus to the same part of the body.

How the Danish team counted cancers

Everyone in Denmark has a personal number that ties together their hospital diagnoses, biopsy reports and any cancer they develop. The team used nationwide Danish register-based data to find people first diagnosed with lichen planus between 1978 and 2020 who had no earlier cancer: 21,650 women and 14,195 men. Patients diagnosed in hospital came from the National Patient Register, and the Danish Pathology Register added both diagnoses from biopsies and the site of each biopsy, sorted into mouth, skin and genitals.

Each person was followed until they died, moved abroad or reached the end of 2023, and any new cancer was taken from the Danish Cancer Register. The researchers then compared the number of cancers in the group with the number expected if the patients had got cancer at the same rate as other Danes of the same sex. That comparison is called a standardized incidence ratio: the observed numbers of cancers divided by the number national rates would predict. A ratio of 7 means seven cancers where one would be expected.

How can a sevenfold risk be about 1 in 100?

Compared to the general population, women with lichen planus had about seven and a half times the expected rate of cancer of the oral cavity, the inside of the mouth, close to seven times the rate of tongue cancer and six times the rate of lip cancer. Vulvar cancer was about two and a half times as common as expected. The cancer risk pattern was similar in male patients. Results were consistent across follow-up, meaning the excess did not fade or build sharply with the years since diagnosis.

Those multiples sound alarming. They sit on top of cancers that are rare to begin with, though. Over 20 years, 0.8% of women and 1.0% of men with lichen planus developed cancer of the oral cavity, and the 20-year absolute risks for genital cancer were 0.4% in women and 0.2% in men. The figures for tongue cancers were 0.5% and 0.6%, and for lip cancers 0.1% and 0.2%. Put another way, for every hundred people with the condition followed for two decades, about one was diagnosed with cancer of the oral cavity, with tongue and lip cancers adding roughly another half to one case on top.

Did the cancers appear where the lichen planus was?

Mostly, yes. Split by where the condition had been confirmed, people with lichen planus in the mouth had the highest rate of mouth cancer, and the same held for genital cancer in patients with genital disease. On the skin the rise was small. Among all women with lichen planus, squamous cell carcinoma, a common skin cancer, was about 1.4 times as frequent as usual, which the authors call a slightly increased risk of skin cancer.

One result ran the other way. Lung cancer risk was decreased, at about seven in ten of the usual number. That figure is hard to interpret on its own, and it is a reminder that people diagnosed with lichen planus may differ from the wider population in ways a ratio does not capture.

Why inflamed tissue might turn cancerous is not settled. The authors of the 2026 meta-analysis point to the long-standing hypothesis that persistent mucosal inflammation contributes to oncogenic progression, the slow slide of cells toward cancer, with the immune attack generating damaging molecules and growth signals over years. That would fit the Danish pattern, in which the excess sat in the mouth and genitals and barely touched the skin, but neither study tested it.

Finland found the same mouth cancer pattern in 13,100 women

Denmark is not the first Nordic country to try this. In 2017 a Helsinki team linked 13,100 Finnish women with lichen planus to their national cancer registry and found much the same picture, with extra cancers of the lip, tongue, oral cavity, esophagus, larynx and vulva. Their oral cavity ratio of about eight is close to the Danish figure of seven and a half, but unlike the Danish team, which found a small rise in skin cancer, they saw none on the skin, reporting that the risk of cancer was not increased at other sites the condition reaches.

Two countries, two sets of registers and two research groups arriving at similar multiples makes the mouth and vulva result hard to dismiss as chance. The Danish study adds men, a larger sample, the site-by-site analysis and the absolute risks that let a reader see how rare the outcome remains.

Smoking, HPV and other gaps in the lichen planus cancer data

The comparison was with the general population, which is how a standardized incidence ratio works, and it leaves several things open. Smoking and heavy drinking raise oral cancer risk on their own, and the 2021 overview lists the consumption of tobacco and alcohol among the factors linked to cancer in oral lichen planus. Infection with the human papillomavirus, or HPV, matters for genital cancers. The 2026 meta-analysis found that earlier studies reported possible distorting factors such as UV exposure, smoking, immunosuppression, and HPV infection only patchily, and the Danish design compares patients with other Danes of the same sex, not with people who share their habits.

A register can also only count what is written down. People with mild skin patches who never reached a hospital or a biopsy are unlikely to appear. The site groups were mouth, skin and genitals, so the erosive mouth form that earlier work singled out is not separated from the milder lacy form in these figures. People with a chronic condition in the mouth may also be examined more often than other people, which could bring some cancers to light sooner. And the work was done in one country, so the figures may not carry over unchanged elsewhere.

Finally, a ratio of this kind shows that cancer followed the diagnosis more often than expected. It cannot show that lichen planus, or its treatment, caused the cancer.

What the Danish results mean for people with lichen planus

The authors put their conclusion in two halves: “While the absolute risk is low, site-specific cancer should be considered a possible long-term complication of LP.” For the mouth, that matches the WHO consensus listing. For the genitals it adds weight to the 2022 vulvar review, which called for regular life-long follow-up of women with vulvar lichen sclerosus or lichen planus.

For lichen planus confined to the skin, the extra risk in Denmark was small, in line with the meta-analysis estimate of close to no cancers in skin cases. How often any one person is examined, and by whom, depends on where their condition is and how it behaves, and is decided with their doctor.

In Denmark, about 1 in 100 people with lichen planus developed cancer of the oral cavity within 20 years, several times the usual rate, and the excess sat where the condition had been, a pattern this kind of study can describe but not explain.