An unexpected cause of bleeding?

This patient presented with an emergency GI bleed. 
WHAT IS THE DIAGNOSIS?

■ Benign gastric ulcer

Hmm, multiple GU's ?!

■ Ulcerated GIST

Multiple ulcerated GIST's. Really?

■ Adenocarcinoma

Multifocal adenocarcinoma ?!

■ Lymphoma

Too crater-like !!!

■ Melanoma

Got it!

explanation

There are actually several odd lesions in the stomach. Apart from the 'multi-focality', the lesions look a little like craters on the moon. Of course, this is what metastatic disease looks like. The dark colour clinches the diagnosis of melanomatous deposits.  Here is a link to Sanjeev's and Ashok's case published in Digestive and Liver Disease [2020;52(12):1512] which is an even better demonstration of that dark pigmentation. 

Malignant melanoma has a peculiar predilection for the gastrointestinal tract. Melanoma can spread anywhere and is the most common metastatic tumor of the GI tract. More often the haematogenous spread is to the small bowel or colorectum. Gastric metastases are uncommon. 

It’s one of the more common findings in the small bowel of younger patients with anaemia.  In an old post mortem series, the prevalence of GI metastasis in patients with melanoma was only 0.9% in 1000 melanoma patients (Arch Surg 1964:88:969-973).  However, when you look at cases with advanced disease, up to 50% will have GI metastases (Cancer 1964;17:1323-39).  As one may expect, the most common presentation is with anaemia or obstructive symptoms.  Interestingly, surgical resection has been linked with a longer survival!  

Of course, its important to distinguish between a primary GI mucosal melanoma and metastatic melanoma. The criteria for a diagnosis of primary intestinal melanoma include 1) no evidence of concurrent melanoma or atypical melanocytic lesion of the skin, 2) absence of extra-intestinal metastatic spread of melanoma, and 3) presence of intramucosal lesions in the overlying or adjacent intestinal epithelium 

In a small series, the 5 year survival was 38% (Arch Surg 1996;131 :975-980).  Without surgical intervention, the prognosis used to be grim and Amer et al. (Gynecol Obstet 1979;149:687-92) reported a mean survival time of 9.7 months, whilst others have reported an even shorter median survival of 4.7 months.   Nevertheless, it is perhaps likely that case selection is the reason for the apparent survival benefit of surgery.  The new checkpoint inhibitors and other immunotherapies are revolutionising the treatment of advanced stage disease.