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According to the results of a study published in the Proceedings of the National Academy of Sciences, a test that assesses the expression of two genes accurately classifies two types of cancer that share a similar appearance but have very different treatment approaches: gastrointestinal stromal tumor (GIST) and leiomyosarcoma.

GIST is a rare type of cancer that originates in the wall of the gastrointestinal track. GIST is thought to originate in the “pacemaker” cells of the digestive system; these cells are responsible for the movement of food or nutrients through the system.

Standard treatment for GIST typically includes surgical removal of as much cancer as possible and treatment with the targeted agent Gleevec® (imatinib mesylate). GIST tends to be unresponsive to standard chemotherapy or radiation therapy.

Leiomyosarcoma is a type of cancer that develops in smooth muscle cells, most commonly in the uterus, abdomen, or pelvis. In contrast to GIST, leiomyosarcoma tends to be unresponsive to Gleevec.

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Distinguishing GIST from leiomyosarcoma can be challenging. Because the two types of cancer require very different treatment, however, accurate diagnosis is very important. In an attempt to improve upon current approaches to distinguishing GIST from leiomyosarcoma, researchers developed and tested a two-gene classifier.

The test assesses the expression of the OBSCN and C9orf65 genes. In patients with GIST, OBSCN tends to be expressed at a higher level than C9orf65. In patients with leiomyosarcoma, the reverse is true. By assessing the relative expression of these two genes, the researchers were able to correctly classify GIST and leiomyosarcoma patients with almost perfect accuracy.

The researchers conclude that this two-gene test appears to very accurately distinguish GIST from leiomyosarcoma. They note “…utilization of this technology may aid clinicians and pathologists in diagnosis and treatment of patients who have tumors that cannot be clearly classified as either GIST or [leiomyosarcoma].”

Reference: Price ND, Trent J, El-Naggar AK et al. Highly accurate two-gene classifier for differentiating gastrointestinal stromal tumors and leiomyosarcomas. *Proceedings of the National Academy of Sciences.*2007;104:3414-3419.