Despite its name, in general it is not considered a true sarcoma, which is a tumor arising from mesenchymal tissue.
The histogenesis of KS remains controversial.
KS may arise as a cancer of lymphatic endothelium and forms vascular channels that fill with blood cells, giving the tumor its characteristic bruise-like appearance.
 KSHV proteins are uniformly detected in KS cancer cells.

KS lesions contain tumor cells with a characteristic abnormal elongated shape, called spindle cells.
The most typical feature of Kaposi sarcoma is the presence of spindle cells forming slits containing red blood cells.
Mitotic activity is only  moderate and pleomorphism is usually absent.
The tumor is highly vascular, containing abnormally dense and irregular blood vessels, which leak red blood cells into the surrounding tissue and give the tumor its dark color.
Inflammation around the tumor may produce swelling and pain.
Variously sized PAS positive hyaline bodies are often seen in the cytoplasm or sometimes extracellularly.

The spindle cells of Kaposi sarcoma differentiate toward endothelial cells, probably of lymph vessel rather than blood vessel origin.
The consistent immunoreactivity for podoplanin supports the lymphatic nature of the lesion.
Despite its name, in general it is not considered a true sarcoma, which is a tumor arising from mesenchymal tissue. The histogenesis of KS remains controversial. KS may arise as a cancer of lymphatic endothelium and forms vascular channels that fill with blood cells, giving the tumor its characteristic bruise-like appearance.  KSHV proteins are uniformly detected in KS cancer cells.
KS lesions contain tumor cells with a characteristic abnormal elongated shape, called spindle cells. The most typical feature of Kaposi sarcoma is the presence of spindle cells forming slits containing red blood cells. Mitotic activity is only  moderate and pleomorphism is usually absent. The tumor is highly vascular, containing abnormally dense and irregular blood vessels, which leak red blood cells into the surrounding tissue and give the tumor its dark color. Inflammation around the tumor may produce swelling and pain. Variously sized PAS positive hyaline bodies are often seen in the cytoplasm or sometimes extracellularly.
The spindle cells of Kaposi sarcoma differentiate toward endothelial cells, probably of lymph vessel rather than blood vessel origin. The consistent immunoreactivity for podoplanin supports the lymphatic nature of the lesion.
Kaposi's sarcoma