SAN DIEGO — Only 15% of melanomas are extracutaneous, but you can easily miss these lesions if you don't keep them in mind during routine skin exams, Terence O'Grady, M.D., said at a melanoma update sponsored by the Scripps Clinic.
The most commonly affected sites for extracutaneous melanoma include the ocular or juxtacutaneous mucosal membranes. (See box.)
“It's easy to miss very small lesions in these places, especially if you don't have really good light in your office,” said Dr. O'Grady, a dermatologist with the departments of medicine and pathology at the University of California, San Diego. “You need to take your time to look at least in these areas.”
He begins routine skin exams by inspecting the patient's scalp and working his way down to the feet. Starting at the scalp “can be a problem in patients with really thick hair, but if you pick through the hair like you're looking for nits, you can examine the entire scalp surface,” he said. “A lot of times, atypical pigmented lesions are present on the scalp. In fact, it's probably more common to have atypical nevi there than to have common nevi.”
Dr. O'Grady also makes it a point to examine the nail beds and the interdigital folds. “These are unusual places to find melanoma lesions, but you can find them,” he said. “One thing I always try to do is have the patient take off their shoes and socks so I can look at the bottom of their feet. That's an important part of the exam.”
Metastatic melanoma is more common in extracutaneous locations, so if you see a pigmented lesion in one of these sites, “consider it a primary melanoma only if you can rule out all possibility of metastasis,” he said. “Sometimes this is difficult or impossible. For example, if a pigmented lesion was removed 10 years ago with no histologic exam, it's going to be hard to prove that this is not a metastasis but is, rather, a primary lesion.”
Ocular lesions comprise about 80% of all extracutaneous melanoma. Pigmented lesions of the eye are the most common. “These will be just like nevi you find in other places, so if you see a nevus on the eyelid, it may be just a nevus and nothing more,” he noted. “If you see pigmentation on the conjunctiva or on the sclera, it may be just a normal melanosis, or it could be a junctional nevus, or it could be something more sinister.”
Part of his routine skin exam involves folding the eyelids to look into the fornices of the conjunctiva, where pigmented lesions, are almost universally something bad. “Those definitely need to be biopsied.” However, Dr. O'Grady added that an ophthalmologist might be referred to because most physicians are not trained to look at ocular lesions.
Another ocular lesion, primary acquired melanosis, can have anything from what looks like melanoma in situ to something as innocuous as hyperpigmentation. “So it doesn't necessarily have to be melanocytic.”
Primary acquired melanosis that involves the limbus is highly suggestive of malignant melanoma. “What's interesting is that you can also see primary acquired melanosis on the conjunctiva that shows extension of lentigo maligna from eyelid skin,” he added.
Poor prognostic indicators of ocular lesions include tumor thickness, pagetoid spread, and involvement of the cornea, episclera, palpebral conjunctiva, or fornix. Sometimes ophthalmologists can successfully treat affected eyes without surgical removal.
The vulva is the next most common site of extracutaneous melanoma, making up about 7% of all cases and typically occurs after menopause, usually discovered late, most commonly on the glabrous skin of the labia minora. Prognosis is grim, with a 5-year survival rate of 47%.
Many cases are amelanotic and resemble discharge or bleeding, “so many of these patients are treated for inflammatory conditions or infectious etiologies before a biopsy is performed,” Dr. O'Grady said.
“What's interesting is that some cases have been diagnosed on Pap smear,” he said. “They actually get the Pap smear back as melanoma cells.”
Estimated Frequency
Eye (78.9%)
Vulva (7.2%)
Soft tissues (2.5%)
Anorectum (2.3%)
Vagina (2.1%)
Upper respiratory tract (1.6%)
Gums and mouth (1.2%)
GI tract (0.7%)
Lung, lip, penis, genitourinary tract, nasopharynx (all less than 0.5%)
Source: Dr. O'Grady