Melanosis of the colon and terminal ileum associated with primary malignant melanoma of the anorectum

A Rare Case of Duodenal Melanosis: Case Report

Pseudomelanosis (PM) is a rare condition of unknown etiology and pathogenesis, described as speckled black pigmentation of intestinal mucosa. It is usually discovered as an incidental finding during endoscopy. Although, etiology of PM is unclear, it has been associated with different medications and systemic diseases such as chronic renal disease and diabetes mellitus. In this report, we describe a case of a 72-year-old male with multiple co-morbidities who presented with epigastric pain, nausea and hematemesis. Subsequently, upper endoscopy performed revealed intestinal PM with no active bleeding. Although considered a benign condition, knowing the existence of PM is important to exclude other serious conditions with similar endoscopic findings.

Primary malignant melanoma of the ascending colon

Malignant gastrointestinal melanoma is usually a metastatic lesion. We report the case of a 67-year-old female patient who presented with intermittent abdominal pain, fever, rigor and diarrhoea. CT scan of the abdomen revealed a large mass at the right iliac fossa with features concerning for intra-abdominal abscess. Exploratory laparotomy confirmed the preoperative diagnosis of abscess, and a right hemicolectomy was performed. Histopathological examination of the surgical specimen was indicative of malignant melanoma, and immunohistochemical examination showed positivity to S100 protein, Melan-A, HMB-45 and vimentin. A series of postoperative clinical, laboratory and imaging examinations revealed no suspicious lesions in the skin, eye, leptomeninges or other sites. Therefore, the diagnosis of primary colonic melanoma was confirmed. Only 36 additional cases of primary colonic melanoma have been reported to date. These rare neoplasms are challenging to diagnose and usually require a multidisciplinary treatment approach, including surgery, chemotherapy and possibly immunotherapy or radiotherapy.

Pathogenesis, diagnosis and management of primary melanoma of the colon

Background

Melanomas within the alimentary tract are usually metastatic in origin. On the other hand, primary melanomas of the gastrointestinal tract are relatively uncommon. There are several published reports of melanomas occurring in the esophagus, stomach, small bowel, and anorectum. The occurrence of primary melanoma of the colon has, however, only been rarely reported. The optimum modus operandi for the management of primary colonic melanoma remains nebulous due to the limited number of reports in literature.

Methods

A comprehensive search of Medline, Cochrane and Highwire was performed using the following keywords: 'melanoma', 'malignant melanoma', 'primary melanoma', 'colon', 'gastrointestinal tract', 'alimentary tract', 'digestive tract', and 'large bowel'. All patients with primary melanoma localized to the colon were included in the review. Patients with metastatic melanomas to the gastrointestinal (GI) tract and primary melanomas localized to the GI tract in anatomic locations other than colon were excluded.

Results

There have been only 12 reported cases of primary melanoma of the colon to date. The average age of patients on presentation was 60.4 years without any significant gender predilection. Right colon (33%) and cecum (33%) were the most common sites for the occurrence of primary colonic melanoma while abdominal pain (58%) and weight loss (50%) were the most common presenting complaints. Colonoscopy is the most reliable diagnostic investigation and offers the additional advantage of obtaining tissue for diagnosis. S-100 and HMB-45 are highly sensitive and specific for the diagnosis of this malignancy. For primary colonic melanomas that have not metastasized to any distant parts of the body, surgical resection with wide margins appears to be the treatment of choice. Although the management was individualized in every case, most of the authors preferred traditional hemicolectomy as the favored surgical approach. Chemotherapeutic agents including interferons, cytokines, biological agents and radiation therapy for brain metastases have been reported as adjuvant and palliative options while considering malignant melanomas in general. The average recurrence-free interval was 2.59 years. Nine of the 12 reports documented follow-up in their patients. Two of these 9 (22.2%) patients died.

Conclusions

Primary melanoma of the colon is a rare clinical entity. Whenever a seemingly primary melanoma is detected in an atypical location such as the colon, it is prudent to conduct a thorough clinical investigation to consider the possibility of metastatic disease. Further studies are needed to document the long term follow-up, survival advantage and safety of the management approaches employed in patients with primary colonic melanoma. Based on current data, surgical resection appears to be appropriate management for primary colonic melanomas; unless the disease has metastasized to distant sites where surgery may have a limited palliative role.

Epithelioid melanoma of the rectum: reappraisal of a deceptive microscopic simulator

We report 2 cases of rectal melanoma. The patients were a 48-year-old man and an 88-year-old woman. In both cases, the tumor presented as polypoid and necrotic masses, making initial diagnostic assessment difficult because of the regressive tissue changes. Microscopically, tumors were mostly composed of epithelioid, highly atypical cells mimicking poorly differentiated carcinoma or large cell lymphoma. Tumor cells were negative for keratin, leukocyte common antigen, and epithelial membrane antigen and positive for S100 protein and several melanoma markers, although in endoscopic biopsy specimens, the positive reaction was focal due to the limited viable tissue. One patient was treated with abdominoperineal resection. Pathologic examination of the surgical specimen revealed a polypoid mass infiltrating the muscle coat of the rectum. Local lymph nodes contained metastatic deposits. Microscopic examination of the rectal mucosa adjacent to the infiltrating neoplasm revealed colonization of the intestinal crypts by atypical melanocytes. This patient is alive 1 year after surgery with no evidence of recurrent disease. The other case was not deemed amenable to radical surgery because of the patient's advanced age and evidence of diffuse metastatic disease. She was alive 6 months after the initial diagnosis but was lost to follow-up. Data indicate that the diagnosis of melanoma, although feasible in large resection specimens, may be problematic in endoscopic biopsy, especially when only small tissue fragments are available and tumor regression hampers the accuracy of immunohistochemical stains. Documentation of intracryptic atypical melanocytes in nonneoplastic mucosa conceptually corroborates claims that rectal melanoma is related to preinvasive precursors as in cutaneous melanoma.

Primary malignant melanoma of the transverse colon: report of a case and review of the literature

Gastrointestinal involvement by malignant melanoma is predominantly a metastatic phenomenon. Although primary malignant melanoma of the gastrointestinal tract has been documented in the esophagus, stomach, small bowel, and anorectum, the incidence of primary melanoma of the colon is rare and remains controversial in most cases. We present a case of solitary malignant melanoma of the transverse colon occurring in a 64-year-old African American male patient. Complete dermatologic and ophthalmologic examinations revealed no evidence of a cutaneous or an ocular primary lesion. Microscopic examination of the resection specimen revealed malignant melanoma, which was confirmed by immunohistochemical positivity for S100 and melan-A. We believe that this tumor represents a primary colonic malignant melanoma.