Angiotropic metastatic malignant melanoma in a canine mammary gland

Abstract

An eleven-year-old spayed female Yorkshire Terrier presented with a sublumbar mass and upon ultrasonographic examination, was revealed to have a mammary gland tumor. Black to reddish colored masses, located in the visceral peritoneum of the sublumbar region was observed on laparotomy with masectomy of the right side. In the laparotomy, we observed reddish masses multifocally located in the serosal membrane of the large intestine. Histopathologic examination of the intestinal and abdominal mass showed highly invasiveness into the muscle and metastasis of melanocytic tumor cells through the blood vessels. The mammary glands showed abnormal hyperplasia of melanocytes, destruction of the normal glands by tumor cells and infiltration of some lymphocytes in the pool of melanocytic cells. We have identified a malignant melanoma containing an angiotumoral complex in which tumor cells occupied a pericytic location along the microvessels with intravasation determined by immunohistochemistry for S100 protein and protein kinase C-α. Histologic findings in this dog lead to a diagnosis of an angiotropic metastatic malignant melanoma.

Keywords: Canine; S100 protein; malignant melanoma; mammary gland; metastasis; protein kinase C-α.

Figure 1

Histopathological findings of the most extensively invaded lesions, skin and mammary glands. (A) Primary invasive melanoma. Abnormal hyperplasia of melanocytes in the dermal layers with hyperactivated epidermis melanocytes. H&E stain. Scale bar=500 µm. (B) Primary invasive melanoma. Note melanoma cells closely opposed to the external surface of microvessel (inset); melanocytic tumor cells invaded into the dermal lymphatic follicle and are hyperpigmented in the dermal reticular layer and more deep layers. H&E Stain. Scale bar=200 µm, (inset, H&E stain; Scale bar=500 µm). (C) Mammary glands also heavily pigmented. Abnormal hyperplasia of melanocytes as well as invasiveness and destruction of normal mammary glands by spindle melanocytic tumor cells. H&E stain. Scale bar=500 µm. (D) Mammary glands also heavily pigmented. Normal mammary glands were invaded with destruction by tumor cells. Pleomorphic round cells arranged in sheets or clusters. H&E stain. Scale bar=200 µm. (E) Malignant melanoma of the peritoneum lesion. Invasiveness and metastasis of melanocytic tumor in abdominal connective tissue and blood vessels. H&E stain. Scale bar=500 µm. (F) Malignant melanoma of the peritoneum lesion. Epitheloid and fusiform neoplastic cells infiltration. H&E stain. Scale bar=200 µm. (G and H) Malignant melanoma of the large intestinal lesion. Invasiveness into the muscle and metastasis of melanocytic tumor cells through the blood vessels and lymphatic channels surrounding glandular ducts. H&E stain. Scale bar=500 µm (G) and 200 µm (H).

Figure 2

Immunohistochemical stain with antibody for vimentin, S100 and PKC-α. (A) Malignant melanoma of the skin. Vimentin expression of mononuclear epitheloid amelanotic melanoma cells. ABC method, Mayer's hematoxylin counterstain. Scale bar=200 µm. (B) Malignant melanoma of the skin. S100 protein immunoreactivity is detected in melanoma cells, which is surrounded by multiple S100-negative epitheloid-shaped cells. ABC method, Mayer's hematoxylin counterstain. Scale bar=50 µm. (C) Malignant melanoma of the skin. Immunodetection of PKC-α in metastatic malignant melanoma. PKC-α expression in the epithelium of microvessels and some peripheral tumor cells. ABC method, Mayer's hematoxylin counterstain. Scale bar=200 µm.