The finding helps answer one of the longstanding questions about Kaposi' s sarcoma and brings researchers a step closer to understanding the nature of the disease. Kaposi's sarcoma behaves so differently from other tumors that it has not been clear whether it derives from one cell or many, or even whether it should be considered a true cancer. This study, which NCI conducted in collaboration with University Teaching Hospital, Lusaka, Zambia, strongly suggests that Kaposi's sarcoma is monoclonal. That is, like other cancers, it has its origin in a single, genetically altered cell which multiplies and spreads.
Most cancers begin with a primary tumor that can later metastasize to other parts of the body.
In Kaposi's sarcoma, however, there is no sign of a primary tumor. Scientists had hypothesized that these lesions arise independently from different cells. To test this idea, Rabkin and his colleagues analyzed the tumor cells from multiple lesions taken from eight women with Kaposi's sarcoma. In each of a woman's cells, one X chromosome has undergone methylation, a chemical change that can inactivate genes. The other X chromosome is unmethylated.