a 64yearold woman presented with 68 sharply demarcated , darkly pigmented macules around the anus ( fig . 1 ) and a 3month history of intermittent rectal bleeding .
the patient underwent a colonoscopy and an ulcerated 3.6 cm in diameter , polypoid , pigmented tumor of the anorectal verge was found ( fig .
based on the patient 's history and physical examination findings , which one of the following is the most likely diagnosis ? 
 peutzjeghers syndrome.genital warts.neurofibromatosis type 1.acrodermatitis enteropathica.metastatic anorectal melanoma . 
 
numerous biopsies were taken from the tumor at the time of colonoscopy and pathologic results were consistent with the diagnosis of melanoma .
histopathology of the operative specimen showed a primary melanoma ( hmb45 and s100 stains positive ) with a breslow thickness of 1.4 mm .
abdominal ultrasonography and contrast ctscan of chest , abdomen , and pelvis showed no evidence of metastases .
anorectal melanoma is a rare disorder , approximately accounting for 1% of all anorectal carcinomas 2 .
the anorectum is the third most common location for melanoma following cutaneous and ocular melanoma .
primary rectal melanoma presents in the fourth decade with an increase of incidence in the fifth or sixth decade of life .
 key clinical messageprimary mucosal melanoma occurs in under 2% of melanomas . 
 anorectal melanoma is a rare disorder , approximately accounting for 1% of all anorectal carcinomas . 
 primary anorectal melanoma presents predominantly in women , in the 4th6th decade of life . 
 typical clinical manifestations include rectal bleeding and tenesmus . 
 the prognosis remains poor . 
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