Malignant Melanoma of Small Bowel: A Rare Case

Melanomas affecting the small bowel are usually metastasis from primary cutaneous lesions. A primary melanoma of the gastrointestinal tract is very rare with reported incidence of just 3%. We present a case of small bowel melanoma with liver metastases. Primary malignant melanoma of the small intestine is quite rare with only a few cases reported in literature. Like its cutaneous counterpart, intestinal melanomas too remains an aggressive disease with a poor prognosis. The overall survival of malignant melanoma affecting the GI tract is 4 to 6 months with a survival rate of less than 10% at 5 years.


Introduction
Malignant melanoma develops from melanocytes which are usually located in the skin, the eye's choroid, the meninges, and the anal margin. Melanoma of the GI tract represents 1 to 3% of the digestive tract cancers. [1] Primary malignant melanoma of the small intestine is quite rare, only a handful of cases have been reported in literature. Like its cutaneous counterpart, intestinal melanoma too remains an aggressive disease with a poor prognosis. The survival of patients with melanoma affecting the GI tract is 4 to 6 months with an overall survival rate of less than 10% at 5 years. [1] Case Report

Figure 1: H & E Stained Slide
We present a rare case report of a 48 year old man who presented with pain in abdomen and weight loss. He already had underwent an ultrasound of the abdomen which was suspicious of liver metastases, before being referred to our side for further management.  • Immuno Histo Chemistry (IHC) markers were positive for S100 and HMB45. • Patient was started on Dacarbazine based palliative chemotherapy.He has completed 2 cycles,and is now due for his 3rd.

Discussion
Primary malignant melanoma of intestine can arise at any site within the GI mucosa, but it is found most commonly in ano-rectal (anal canal, 31.4%; rectum, 22.2%) and oropharyngeal (32.8%) region, oesophagus (5.9%), stomach (2.7%), small intestine (2.3%), gallbladder (1.4%), and large intestine (0.9%). Melanoma develops primarily in the melanocytes, which are the dendritic cells present in the skin, the eye, the epithelium of the nasal cavity, oropharynx, anus, vagina, and the urinary tract. In addition to these sites, melanocytes are present in Meckel's diverticulum. [1] Normally small intestine and colon do not contain melanocytes. Embryologically, the origin primary melanoma of small intestine is because of the melanoblastic cells of the neural crest that migrate to the distal ileum through the omphalomesenteric canal There these cells differentiate by amine precursor uptake and decarboxylation (APUD), and can undergo neoplastic transformation in non-cutaneous site, [1] although some authors still deny the existence of primary melanoma in the gastrointestinal tract. They argue that primary cutaneous tumors can regress before metastatic manifestations or they are too small to be identified by clinical and laboratory examinations. Primary or secondary gastrointestinal melanoma is very difficult to establish resulting in many controversies. [1] The gastrointestinal tract is the most common site for the metastases of cutaneous malignant melanoma. [1] Metastases are usually asymptomatic and are diagnosed at autopsy in 58% of patients with cutaneous malignant melanoma. [1] However, some gastrointestinal melanomas remain undocumented and without evidence of a primary lesion, cutaneous or elsewhere, even after a thorough examination. There are four different types of metastatic melanoma of the small intestine that are solely based on histopathological features: cavitary, infiltrating, eccentric, and polypoid. [1] To make the diagnosis of primary malignant melanoma of the small intestine, one should exclude any history of melanoma in the other major sites. It is very difficult to differentiate between primary intestinal melanoma and intestinal metastatic deposit of melanoma solely based on histopathological features alone. Primary instestinal melanoma tends to be more aggressive and is associated with worse prognosis than cutaneous melanoma. The mean age at the time of diagnosis of primary GI melanoma is around 54 yr and 75% patients have mesenteric lymphadenopathy. [1] According to Cheung et al. most common site being distal jejunum and ilium.
In our case, histological study confirmed the diagnosis of intestinal melanoma with concordant immunohistochemical profile; our patient had no history of cutaneous melanoma, and examination found no other sites of the disease.

Conclusion
In patients who have liver metastases with unknown