A 45-year-old woman in Portugal grew 1.25-inch-long (3 centimeters) eyelashes in three weeks while being treated with a drug for stage four metastatic colorectal cancer.

Describing the patient's case in the journal BMJ Case Reports, Leonor Vasconcelos Matos and colleagues report the woman was diagnosed with colorectal cancer in November 2017, with examinations revealing multiple pulmonary and liver metastasis that could not be removed. Due to this and other factors, the team decided to treat the woman with the cancer drug cetuximab.

After 14 cycles, she went to the Lisbon oncology clinic with eyelid infections. She noted that three weeks prior, her eyelashes had begun to grow abnormally long and curly. Rather than being pleased with her lengthened lashes, the condition was causing her trouble. 

“People often come to me and say ‘where have you made your eyelashes, they look so real’. This is the fun part,” the patient said in the case study. “The not so fun part is the discomfort and itching that the long eyelids cause, and when you scratch with your hands, the more likely it is to make infections. And this is terrible. I totally agree that I should keep treatment, because it is helping me, but I just wish there was a more easy way to manage my ‘beauty problem.’"

A side effect of cetuximab is skin and hair toxicities. Trichomegaly – defined as the curling, pigmentation, or lengthening of eyelashes (12 mm or more) – is one such effect, usually occurring after 2-5 months of treatment. Although it appears to be harmless, it is in fact a recipe for discomfort as eyelid infections and corneal ulcerations are prone to occur. 

To manage the side effect, the team recommended she shorten and clean her eyelashes every 2-4 weeks with the help of a beautician. In doing so, “the patient reported a marked improvement in her quality of life,” according to the authors. 

Apart from drug-related trichomegaly, the condition can also be congenital. Cetuximab works by binding and inhibiting the epidermal growth factor receptor (EGFR), which can be expressed in some normal tissues as well as tumors, including those of the colon and rectum. Skin toxicity is a common side effect of the agent, happening in up to 80 percent of cases, 15 percent of which are severe. 

Apart from skin cancers, colorectal cancer is the third most common cancer in the United States, according to the American Cancer Society. In 2019, they estimate 101,420 new cases of colon cancer and 44,180 cases of rectal cancer.

The outcome of the woman's cancer treatment was not reported.