Kaposi sarcoma is unique among cancers because most tumors grow from a small number of different cells, whereas nearly all other cancers arise from a single cell, according to a study published online July 10 in the Journal of the National Cancer Institute.

Kaposi sarcoma, which is often associated with AIDS, primarily affects the skin. But as the disease progresses, it can move to the lymph nodes and internal organs as well.

Renan Duprez, Ph.D., of the Institut Pasteur in Paris and colleagues performed the largest study to date on the origins of advanced Kaposi sarcoma. Biopsies from 98 Kaposi sarcoma patients were analyzed using molecular diagnostic techniques to compare the viral DNA of the tumors, which often contain human herpesvirus 8.

The researchers found evidence that nearly 80% of the tumors arose independently from multiple cells. They concluded that few Kaposi sarcoma tumors originate from a single cell and that Kaposi sarcoma, especially in its advanced form, is not true metastatic cancer.

In an accompanying editorial, Parkash Gill, M.D., of Norris Cancer Hospital and Research Institute in Los Angeles recommends what should come next in Kaposi sarcoma research.

With some resolution as to the clonal nature of [Kaposi sarcoma] of the skin and lymph node, similar analysis remains to be done for visceral [Kaposi sarcoma], which can be more invasive leading at times to catastrophic organ dysfunction and even death. It is also not known if the clonal [Kaposi sarcoma] lesions identified in this study were more aggressive and less likely to respond to therapy, Gill writes.