Xolair is associated with a slightly higher risk of cancer, but cancer specialists have determined that this does not mean that Xolair causes cancer. Research has shown that cancer occurred in 20 out of 4127 trial participants (0.5% of Xolair-treated study volunteers) and 5 out of 2236 (0.2%) of people who were assigned an inactive treatment. The most common cancers seen were those of the breast, skin, prostate, and parotid gland. An increased incidence of cancer was not seen in children ages 6 to 12 years who took Xolair.

Xolair is an injectable preparation that works by preventing IgE from binding to IgE receptors on mast cells and basophils and may be used to treat allergic asthma, nasal polyps, and chronic idiopathic urticaria.