The absence of change over time supports benign disease, while progression suggests a cancer.

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Research has also shown the hormones in birth control pills can help prevent ovarian cysts, benign breast disease and acne.

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Novartis says it hopes next year to apply for approval for three additional drugs for various tumors types, including a new treatment for ovarian cancer, a new lymphoma medicine and a drug for Cushing's disease, a benign tumor in the pituitary gland.

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Professor Michael Shaw, a plant health expert at the University of Reading, who was not involved in the research, said it was a step towards understanding why certain strains of the fungus cause disease while others are benign.

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Some 22 percent of people with the disease have the type of lymphoma that typically follows a benign course, Lichtenfeld said.

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Dr. SPIESEL: In the old days, chicken pox was thought to be so benign that it was thought that well, it would be convenient if you could control when children would get the disease.

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