Although these truly "hidden" melanomas are relatively uncommon in comparison to areas of the body that are seen more or less every day, they are important to know about because they are more likely to be discovered at a more advanced stage.

Before, during or after reading this discussion, you may wish to review criteria for assessing your risk for developing melanoma and for conducting a whole-body self-examination for melanoma (Click on Who Is at Risk and Self-Examination in the Main Menu). Remember that self-examination should include "hidden" areas such as web spaces between fingers and toes, genitalia, skin folds in areas such as the armpits and genitalia, and the hair-bearing scalp. The scalp should be examined by systematically parting the hair until the entire scalp is examined; a blow-dryer may be useful in parting the hair. Routine gynecologic, ophthomologic and dental examinations should include examination for pigmented lesions.

The great majority of melanomas are cutaneous melanomas—melanomas that develop on the skin. While many cutaneous melanomas develop on sun-exposed areas of the body, most melanomas develop on body areas that are under clothing much of the time (torso and buttocks) or are difficult to self-examine (back, buttocks, backs of the thighs and legs, scalp, and behind the ears).

Melanomas that might be defined as "hidden" are those that develop in areas of the body where they are "out of sight, out of mind": under fingernails and toenails; in mucous membrane tissue of the nose, mouth, genitalia and anus; skin of the hairy scalp; ears; on the soles of the feet; and, in the mucous membranes of the eye. There are also the extremely rare melanomas that develop as an apparent primary lesion originating in an internal organ such as the liver, lung, esophagus, gall bladder, middle ear, brain and intestine.

Subungual Melanoma

Subungual (under a nail) melanoma is a rare form that occurs with about equal frequency in males and females. Its incidence is about 2 percent of melanomas in whites and up to 30-40 percent of melanomas in non-whites. It can occur at any age; the median age is 50+ years. It can occur under the nail of any finger or toe, but occurs most frequently under the nail of a great toe or thumb.

Because the most common sign of an early subungual melanoma is a brown to black discoloration ("nail streak") under the nail in the nail bed, the development of melanoma can easily be mistaken for a subungual hematoma (bruise). The mistaken identification is often supported by recollection of recent finger or toe trauma—e.g., stubbing a toe, dropping a weight on a finger or toe, etc. Mistaking a subungual melanoma for an under-the-nail bruise is a common reason for delay in seeing a dermatologist or other physician. It should be noted that nail streaks (pigmented nail matrix nevi) occur quite commonly in deeply pigmented people and only rarely in white-skinned people. A lesion suspected of being atypical, or early melanoma of the nail structure, can include a black streak, very wide brown streak, or variegated brown streak, regardless of race.

Subungual melanoma can be suspected when (1) a "nail streak" appears in the absence of recent trauma, (2) the nail discoloration does not gradually disappear as a hematoma would do, or (3) it increases in size over time. Pigmentation of the nail fold (skin next to the nail), or destruction/deformation of the nail plate are indications of more advanced subungual melanoma.

Suspected subungual melanoma should be examined by a dermatologist as soon as possible. Biopsy is the only certain method of diagnosis if a melanoma is suspected. Early melanoma is treated by surgical excision. More advanced melanoma may require amputation of the affected finger or toe, investigation and possible removal of regional lymph nodes, and regional or systemic chemotherapy.

Mucosal Melanomas

Primary melanomas can arise in mucosal tissue lining the nose, mouth, esophagus, anus, urinary tract, and female genitalia. Although mucosal melanomas are relatively rare, they tend to be well advanced when diagnosed—probably because the mucosal tissues are "out-of sight, out-of-mind" and infrequently self-examined or impossible to examine easily (sinus membranes, nasal passages, anus and rectum).

Mucosal Melanomas of the Nose and Mouth

The nose and mouth are the most common sites of primary mucosal melanomas (melanomas that originate at those sites). Treatment is often delayed because early symptoms are minor and often ignored or misinterpreted:

• Nose—nosebleeds and nasal stuffiness may be misinterpreted as "sinus trouble"
• Mouth—a pigmented mass and pain on swallowing may be misinterpreted as a "canker sore" or "sore throat"; if the melanoma causes pain, it is probably quite advanced; an annual oral examination by a physician may detect melanoma in the mouth area before it is well advanced
• Nasopharyngeal—inflammation of the inner ear (otitis media) may be misinterpreted as an ear infection

Surgery is the preferred initial treatment for melanoma at these sites.

Mucosal Melanoma of the Female Genital Tract

The genital tract accounts for a small percentage of melanomas diagnosed in women:

• Vulva—Melanomas can arise on the labia minora, labia majora, or clitoris, and may extend into the vagina. The most common symptoms are bleeding and itching that a patient may mistakenly identity as menstrual irregularity or vaginal infection. Most patients with advanced melanomas have symptoms and have recognized a change in size, shape or color of a mole on the vulva. Most melanomas are discovered by a physician during a gynecologic examination. Complete surgical excision is the preferred treatment for melanoma of the vulva.
• Vagina—Vaginal melanoma that is not an extension of vulvar melanoma is very rare. The common symptoms of advanced disease are vaginal bleeding, foul odor and discharge, and vaginal pain. Most advanced lesions cause symptoms and are diagnosed during gynecologic examination. Complete surgical excision is the preferred treatment for vaginal melanoma. Early, curable melanomas of the vagina are usually asymptomatic and are only detected during examination of these sites.

Anorectal Mucosal Melanoma

Rectal bleeding is the most frequent symptom of advanced anorectal melanoma and there may be a painful rectal mass that the patient mistakenly believes to be a hemorrhoid. Early lesions usually cause no symptoms. An anorectal melanoma may be well advanced before it is brought to the attention of a physician. Surgical excision is the treatment for anorectal melanoma. Lymph node biopsy, lymph node investigation and systemic chemotherapy may be necessary when melanoma is more advanced.

Mucosal Melanoma of the Urinary Tract

• Males—Melanoma of the penis is more frequent on penile skin than in mucosal tissue of the urinary tract (urethra). Symptoms of advanced urethral melanoma are blood in the urine and painful urination. Most early melanomas of the penile skin or urethra cause no symptoms.
• Females—Melanoma of the urethra may cause symptoms of frequent urination, painful urination, or urinary obstruction. Early lesions usually cause no symptoms.

Mucosal Melanoma of the Esophagus

Primary melanoma of the esophagus is extremely rare. Symptoms of advanced tumors include difficulty swallowing, regurgitation, pain, and esophageal bleeding. Early lesions usually cause no symptoms.

Cutaneous Melanoma of the Hairy Scalp

Cutaneous melanoma of the hairy scalp can be a "hidden" melanoma because (1) the scalp is difficult or impossible to self-examine, (2) there may be no symptoms until the melanoma is well advanced, and (3) the scalp is usually "out of sight, out of mind." A well-developed cutaneous melanoma of the hairy scalp is shown in this photo:

A brown-black plaque was present on the scalp of a 65-year-old woman for several years. Although noted several times by a family member, it was not regarded as a "dangerous" lesion. When the lesion became large enough to cause problems in combing her hair, the woman sought medical attention. The lesion was diagnosed as superficial spreading melanoma and surgically removed.

Ocular Melanoma

Primary melanoma can develop in the lining of the eyelids (conjunctiva) or in the thin pigmented coating within the eyeball (choroid). Conjunctival melanoma may be initially identified when a patient looks for the cause of "scratchiness" under the eyelid. Choroidal melanoma is often noticed first during an ophthalmologic examination for eyeglasses, or the patient may note a "dark spot" on the eyeball near the lens. Choroidal melanoma may metastasize, so early diagnosis and treatment are essential. A person with suspected ocular melanoma should be seen as soon possible by an ophthalmologist. The management of patients who have ocular melanoma is beyond the scope of this review

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