anorectal melanomas comprise approximately 1% of all melanomas and about 0.52% of all anorectal malignancies . common presentations for anorectal melanoma include rectal bleeding , anorectal pain , change in bowel habits or a rectal mass . therefore , given the lack of pathognomonic clinical complaints , early diagnosis is difficult to make . this represents a significant clinical challenge since early diagnosis and treatment are crucial . conventionally , therapy for anorectal melanoma consists of a complete surgical resection of the tumor for local control of the disease . this can be done by means of sphincter- sparing wide local excision ( wle ) or abdominoperineal resection ( apr ) in cases of large tumors or when wle is not feasible . radiotherapy may be used to enhance regional control but has no impact on overall survival . the majority of patients progress to metastatic disease , and the use of chemotherapy has been advocated in such cases to improve the overall survival . in april 2013 , a 71-year - old female with no significant past medical history presented to our institution with painful bowel movements for the last 3 months . the patient also noticed blood - streaked stools and reported a 16-lb unintentional weight loss over a 1-year period . the review of her systems was negative otherwise . on examination : the woman was 5 7.5 ( 1.715 m ) tall , weight was 172 lb ( 78.019 kg ) , with a bmi of 26.54 , and her vital signs were normal . digital examination of the rectum revealed two small hemorrhoids at the 6 o'clock position and a firm , nonobstructing mass near the anal verge . the patient underwent a colonoscopy in september 2013 which revealed a nonobstructing , ulcerated anal mass , approximately 1 cm from the anal verge . stains for ck5/6 and p63 were positive , likely suggesting a primary squamous cell carcinoma of the anus . a ct of the abdomen and pelvis demonstrated an abnormal mass at the anorectal junction , with no evidence of lymph nodes or liver metastases in september 2013 ( fig . pet combined with a ct scan demonstrated marked metabolic activity in the primary anal mass and a 1-cm perirectal lymph node near the coccyx , suggesting a node - positive disease in october 2013 ( fig . the patient 's tumor was sent to an outside institution for a second opinion , and the report was concluded as the tumor may in fact be a malignant melanoma . the patient subsequently underwent an exploratory laparotomy with an apr and left - end colostomy in october 2013 . the pathologic specimen confirmed a malignant melanoma arising in the anal skin and extending into the rectum , involving the anal and perirectal soft tissue and 6 regional lymph nodes ( fig . the tumor was classified as grade 3 , poorly differentiated , stage iiia , t2n1m0 according to the tumor - node - metastasis classification of colorectal cancer . immunohistochemical analysis results were positive for the expression of the s-100 protein , hmb-45 and vimentin , whereas negative for the expression of cytokeratin and sma ( fig . the patient agreed to the plan of starting chemotherapy with mitomycin and 5-fluorouracil ( for the anorectal melanoma ) . primary malignant melanoma of the anus and rectum is a rare and highly lethal malignancy of the elderly , which often manifests at an advanced stage . mucosal melanomas represent approximately 1.2% of all melanomas and anorectal melanomas account for less than 25% of all mucosal melanomas . in addition , it is the most common primary melanoma of the gastrointestinal tract   and accounts for approximately 0.5% of all colorectal and anal cancers . the tumor commonly affects females in their fifth or sixth decade [ 9 , 10 ] with a 1.7-fold higher prevalence in caucasians than in african americans . the incidence rate is reported as 0.4% per million   with a 1.8-fold increase in incidence in the last 2 decades , suggesting either a true increase in incidence or an improvement in diagnosis . a melanoma of the anus and rectum was first reported by moore   in 1857 . lesions can affect the anal canal , the rectum or both , with the majority occurring within 6 cm of the anal rim . common presenting symptoms include rectal bleeding , anorectal pain or discomfort , change in bowel habits , prolapsed tumor mass and hemorrhoids . primary anorectal malignant melanomas are in almost 80% of the times mostly misdiagnosed as hemorrhoids , polyp , adenocarcinoma or rectal ulcer . grossly , the majority of lesions appears polypoid , with or without pigmentation , and can be ulcerated as well . the tumor is amelanotic in about 30% of the cases , and with considerable morphologic variability , misdiagnosis as lymphoma , carcinoma or sarcoma is common [ 14 , 15 ] . the use of immunohistochemistry panels , including s-100 proteins , melana , hmb-45 and tyrosinase , can help in the diagnosis . in our case , chute et al .   reported 4 histologic cell types : epithelioid , spindle cell , lymphoma - like and pleomorphic . the mitotic rate averaged 2.8 mitotic figures per high - power field in 17 cases of a primary anorectal malignant melanoma . it is presumed that primary anorectal malignant melanoma arises from normal melanocytes in the intestinal epithelium distal to the dentate line and extending proximally into the rectum . kit expression can be present in anorectal malignant melanomas and , when present in spindle cell subtypes , can lead to confusion with gastrointestinal stromal tumors . as in cutaneous melanomas , loss of c - kit expression is associated with aggressive clinical behavior , it was postulated that a loss of kit might play a role in the pathogenesis [ 5 , 17 ] , therefore suggesting a role of kinase inhibitors such as imatinib . the 5-year survival rate has been reported to be less than 20% for anorectal melanomas , with a median survival of 24 months . prognostic factors include the stage of the disease at the time of diagnosis   and the tumor thickness . as this is a relatively rare entity , we lack randomized control trials regarding appropriate management , and current evidence is mostly based on retrospective studies , reported as a limited number of cases or data collected over prolonged time periods , including patients with an age of up to 64 years [ 21 , 22 ] . a meta - analysis of 426 patients did not demonstrate any survival advantage with either approach . studies reported that local disease seems to be more effectively controlled with apr [ 21 , 25 , 26 ] . recent studies suggested the initial treatment of choice to be wle because radical surgery failed to show any survival advantage and also to avoid the need for colostomy [ 25 , 26 ] . radiation therapy has reported to provide a better local control after wle   and also seems beneficial for sphincter preservation . most patients die regardless of the chosen therapeutic strategy due to the aggressive nature and the rapid progression of the tumor . kim et al .   conducted a retrospective review on 18 patients with metastatic anorectal melanoma treated with cisplatin - based chemotherapy in combination with interferon alpha-2b or interleukin-2 . the authors declare that there are no conflicts of interest regarding the publication of this paper .