If you're thinking about getting a tattoo, you might want to think twice about where you put it. That's because getting a tattoo over a mole or birthmark could cause any signs of a melanoma to go unnoticed.

A 29-year-old German patient was undergoing a laser removal procedure for his tattoo when specialists found a cancerous mole that had been hidden by the tattoo's black ink, according to case report in JAMA Dermatology.

The patient went for laser removal of his tattoo, which covered both arms and his chest, and was initially told that he should have his mole removed, however, the laser specialists weren't able to determine whether the mole was cancerous because of the skin's pigmentation from the ink - the man refused to get it removed. Seven years, and 43 sessions later, the specialists denied further treatment unless the mole was removed, MedPage Today reported.

A biopsy of the mole discovered a superficial malignant melanoma, the most common form of melanomas, accounting for 70 percent of all cases. It grows along the top layer of skin before moving deeper into the body. Because of this pattern of growth, the melanoma wasn't able to spread any further into the patient's body.

"Fifty percent of all melanomas develop in pre-existing moles," Dr. Hooman Khorasani of the Icahn School of Medicine at Mount Sinai, in New York City, told HealthDay. Tattoo removal can also make it harder to see a cancerous mole, since the lasers also remove any pigmentation that the melanoma cells, called melanocytes, make.

"Therefore, any irregular pigment that one would expect to detect will not be detected as easily," he said. "This is the reason that some subtypes of melanoma, called amelanotic melanomas, are more dangerous."

The authors of the report also mentioned 16 previous cases of malignant melanomas on people with tattoos. For some of these cases, laser treatment led to misdiagnosis, delays in diagnosis, and death.

According to the National Cancer Institute, an estimated 76,690 new cases of melanoma will develop in 2013.

While the inks used for tattoos may hide moles, they haven't been shown to promote growth of melanomas.

"Dermatologists have been evaluating patients with tattoos for decades for any evidence of skin cancer, and they have never found an increased prevalence of the disease in those individuals," Dr. Ariel Ostad, assistant clinical professor of dermatology at New York University School of Medicine, wrote on the Skin Cancer Foundation's website.

"The same is true for patients who have already had melanoma or another form of skin cancer; the inks used in tattoos have never been shown to increase their risk of recurrence. People who have had skin cancer are always at higher risk of developing future skin cancers, but tattoos do not increase that risk."

Source:

Pohl L, Kaiser K, Raulin C. Pitfalls and Recommendations in Cases of Laser Removal of Decorative Tattoos With Pigmented Lesions: Case Report and Review of the Literature. JAMA Dermatology. 2013.