Primary malignant melanoma of the esophagus: A rare disease

A 63-year-old man consulted his primary care physician with complaints of mild dysphagia for solids and loss of 5 kg in the last three months. No known medical history. The physical examination did not reveal any changes and the laboratory study was normal.

Computed tomography (CT) showed an intraluminal mass with contrast enhancement in the middle third of oesophagus, measuring about 8 cm, suspected of oesophagal neoplasia (Figure 1). There was also a pulmonary nodule measuring 13 mm in the right lung.

Endoscopy confirmed the existence of a large lesion, about 28 cm from the upper dental arch, which occluded 60% of the oesophagal lumen (Figure 2). Biopsies and immunohistochemical studies were compatible with malignant melanoma: diffuse positivity with HMB45 and S-100 protein; negativity with p63 and CK20.

Positron emission tomography (PET-CT) revealed intense 18F-FDG uptake in the oesophagal mass and focal uptake of the pulmonary nodule, compatible with malignancy (Figure 3). The biopsy of the pulmonary nodule proved to be a metastasis of melanoma.

The detailed clinical examination did not find suspicious lesions of melanoma on the skin, oral cavity, eyes, and anus, so the diagnosis of primary oesophagal melanoma was assumed.

Melanoma is most commonly found in the skin, but it can appear in the uvea, genitourinary tract, digestive tract, and leptomeninges [1]. Primary malignant melanoma of the oesophagus is a rare, but aggressive tumour with a reported prevalence of 0.1–0.5% of all oesophagal malignancies [2]. The average age at diagnosis is 60 years old and is more common in men (2:1) [1,2].

Melanocytes exist in small quantities in the squamous epithelium of the oesophagus and are the precursors of malignant melanoma [1]. It is more frequent in the lower and middle thirds of the oesophagus (90% of cases), probably because it is where there is a greater concentration of melanocytes [1,2].

Clinically, primary oesophagal melanoma presents similarly to other oesophagal malignancies and the symptoms are nonspecific [3]. The most frequent symptoms are dysphagia, epigastric pain, and weight loss [1,4].

CT identifies the intraluminal mass, its location and evaluates whether there is mediastinal invasion, nodal enlargement, and distant metastatic disease. However, the findings are nonspecific and it is only possible to distinguish melanoma from other differential diagnoses through endoscopy with biopsy and immunohistochemical studies [1].

Endoscopically, it usually appears as a solitary polypoidal mass that may be pigmented or non-pigmented (depending on the amount of melanin), covered with normal mucosa [1,3-4]. The final diagnosis is confirmed by immunohistochemical studies: the primary malignant melanoma of the oesophagus reveals positivity for S- 100 protein and HMB-45, and negativity for cytokeratin and CEA, which confirms the diagnosis of melanoma and exclude carcinoma [1-2,5].

However, it is important to exclude that it is a metastatic lesion and the diagnosis of primary oesophagal melanoma can only be accepted in patients with no history of melanoma and no evidence at physical examination of pigmented lesions involving the skin or other mucous membranes[2]. The PET-CT is useful to establish the staging and follow-up of this tumour [2].

The diagnosis is usually made in advanced stages and it has a worse prognosis than other primary malignant tumours of the oesophagus, with a mean survival rate of less than 5% at 5 years[3,4]. About 40-50% of patients have metastases at the time of diagnosis, most frequently in regional lymph nodes, liver, and lungs [1-2,5]. Surgical resection is the only curative treatment [1-3].

Primary malignant melanoma of the oesophagus is rare, but with a poor prognosis. It must be considered by radiologists in the differential diagnoses of oesophagal polypoid masses seen in imaging studies, as early diagnosis improves the survival rate.

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