Nov. 9, 2010 (Atlanta) -- People with systemic lupus are 15% times more likely to develop cancer compared with the general population, suggest findings of a study involving nearly 13,500 people with systemic lupus.
The higher malignancy rate among people with systemic lupus is driven mainly by an increased risk of cancers of the white blood cells, particularly a threefold increased risk of lymphoma, says researcher Sasha R. Bernatsky, MD, assistant professor in the divisions of rheumatology and clinical epidemiology at McGill University in Montreal.
Because lymphoma is a relatively rare cancer, however, the absolute risk of any person with lupus developing it is still quite low, she tells WebMD.
"If you follow 200 patients with lupus for a year, maybe you would see one lymphoma," Bernatsky says. "Although important ... we don't want to be overstating the finding."
Not all the news is bad. In what she calls one of the most surprising findings, she says that women with systemic lupus were less likely to develop estrogen-sensitive cancers, specifically those of the breast (30% decreased risk), endometrium (51% decreased risk), and ovary (44% decreased risk).
"This raises the possibility that something about how women with lupus metabolize estrogen may be involved," Bernatsky says.
She presented the findings here at the American College of Rheumatology Annual Scientific Meeting.
More Cancer Cases Than Expected Among People With Systemic Lupus
Systemic lupus is a chronic inflammatory disease that can affect the skin, joints, nervous system, kidneys, lungs, and other organs in the body. The most common symptoms include skin rashes and arthritis, often accompanied by fatigue and fever. Lupus occurs mostly in women and typically develops in people in their 20s and 30s.
The same research group previously demonstrated an association between systemic lupus and cancer in a smaller study. The current study was designed to more precisely estimate cancer rates among people with lupus, compared with the general population.
The study involved 13,492 people with lupus from 24 medical centers followed for an average of nine years. Using regional tumor registries, the researchers pinpointed people with systemic lupus and compared their cancer rates to what was expected in the general population.
Over the course of the study, 632 cases of cancer were noted among people with systemic lupus, "more than what we expected," Bernatsky says.
Younger Women With Systemic Lupus at Particularly High Risk of Cancer
Compared with the general population, people with systemic lupus were:
- 3.4 times more likely to develop non-Hodgkin's lymphoma
- 3.2 times more likely to develop any lymphoma
- 2.8 times more likely to develop vulvo-vaginal cancers
- 2. 2 times more likely to develop liver cancer
- 1.7 times more likely to develop leukemia
- 1.7 times more likely to develop cervical cancer
- 1.2 times more likely to develop lung cancer
"When stratified by age, people with lupus who are younger than 40 appear to have a particularly high risk. They are 1.7 times more likely to develop cancer than the general population," Bernatsky says.
Drugs, Disease May Drive Tumor Growth in People With Systemic Lupus
The study does not prove cause and effect, and no one knows for sure why people with lupus are at increased risk of certain cancers, Bernatsky says.
"The drugs used to treat lupus may play a role," she says. "But there is just as much evidence that lupus itself may drive tumor growth."
"It's important for these women to get regular Pap smears," Bernatsky says.
People With Arthritis Also Have Higher Cancer Rates
Timothy Beukelman, MD, a rheumatologist at the University of Alabama at Birmingham, tells WebMD that cancer rates are also higher among people with rheumatoid arthritis, compared with the general population.
As with systemic lupus, the immune system is inappropriately turned on in RA, causing inflammation and organ damage, in this case, primarily in the joints.
"In adults with [rheumatoid] arthritis, there is evidence to suggest that both the disease and the drug methotrexate [that is often used to treat it] contribute to an increased risk of malignancy, he says.
More research is needed into the link between cancer and all types of rheumatic disorders, Beukelman says.
This study was presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.