Report on a case of liver-originating malignant melanoma of unknown primary

Abstract

Malignant melanoma (MM) frequently occurs in the skin or mucosa, whereas malignant melanoma of unknown primary (MUP) is diagnosed in patients with lymph nodes or visceral organs as the site of origin, where it is challenging to detect the primary lesion by comprehensive examination. MUP is possibly related to the spontaneous regression of the primary lesion. In addition, primary hepatic melanoma (PHM) usually refers to the primary MM occurring in the liver, with no typical primary lesions and no manifestations of tumor metastasis. A 61-year-old male patient with liver as the site of origin was diagnosed with MM by Melan-A, HMB-45, and S-100 immunohistochemistry staining of liver biopsy tissue. Based on a comprehensive examination, no basis was found for melanoma in sites such as the skin, mucosa, five sense organs, brain, digestive tract, respiratory tract, or genitalia, and the patient was subsequently diagnosed with MUP. MMs require a comprehensive inspection, beginning with the liver, to search for the primary lesion; if the primary lesion is not found, the possibility of PHM or MUP should be considered.

Keywords: diagnosis; liver; malignant melanoma; unknown primary.

Figure 1

MRI shows diffuse space-occupying lesions of the liver, T1WI high signal (a), T2WI low signal (b), DWI high signal (c), and unequal enhancement of foci in the arterial phase (d).

Figure 2

PET-CT shows an increase in the SUV uptake value in multiple parts of the body (a), such as the liver and spleen (d), sternum and vertebrae (b), and other parts of the bone (c).

Figure 3

Liver histopathology (HE ×100) reveals nestlike cellular infiltration, accompanied by more pigmentation and nuclear enlargement with evident heteromorphism (a); the histopathology of pigmented nevi posterior to the left scapula (HE ×100) indicates benign cutaneous nevus (b).