Answer: Metastatic malignant melanoma

Histology: The case is that of a large liver mass associated with extensive necrosis. The mass is composed of confluent nodules of large cells with abundant pink cytoplasm and large nuclei with prominent nucleoli. The cells tend to grow in large sheets and cords and do not show evidence of any glandular or squamous differentiation. In addition, no obvious bile pigment is identified within the cells.

Discussion: This case raises basic differential diagnosis between a primary hepatocellular carcinoma versus a metastasis of a large pink-cell tumor to the liver. The history is helpful in such cases, particularly if the patient is known to have a previously known primary. Immunohistochemistry can be particularly helpful in distinguishing between undifferentiated carcinoma and malignant melanoma and it is also helpful in further defining the carcinoma if the tumor is indeed epithelial in origin. In this case, stains for keratin were negative. The tumor stained positively for HMB-45and Melan-A, helping to establish the diagnosis of metastatic malignant melanoma. Other large pink cell tumors which would enter into the diagnosis in addition to hepatocellular carcinoma would include tumors from the kidney and adrenal gland which can be tumors with abundant pink or clear cytoplasm. In this case, the patient had a known history of malignant melanoma, making the diagnosis somewhat easier.