The New York Post reports that allergy sufferers are less likely to get cancer. They cite the results of several studies which find negative relationships between allergy and various types of cancer, including leukemia, ovarian cancer, non-Hodgkins lymphoma, as well as stomach, pancreatic and brain cancers.
These findings make some sense to me as an outsider to the science, inasmuch as allergy is simply the immune system working too hard. Perhaps an overactive immune system detects and kills cancers before they can become dangerous? Certainly, one approach to curing cancer has been to try to get the immune system to attack it.
So blow your nose, take your antihistamines, and hope your allergies are protecting you, to some degree, against many forms of cancer.