CHICAGO – Comorbid autoimmune disease is associated with a greater chance of survival among women with stage IV breast cancer, according to a retrospective study presented at the annual meeting of the American Society of Clinical Oncology.
“It’s counterintuitive that, if you have two diseases instead of one, that you live longer, so then we had to scratch our heads a little bit and think about why these people are living longer,” said lead author Demitrios Dedousis, MD, University Hospitals, Case Medical Center, Cleveland.
Dr. Dedousis and colleagues conducted a retrospective analysis of patients from Surveillance, Epidemiology, and End Results–Medicare databases between 2007 and 2014 with breast cancer. The study included data from 137,324 patients diagnosed between 2007 and 2012, before the widespread use of immunotherapy. 27% of patients had an autoimmune disease, most commonly rheumatoid arthritis (23%), psoriasis (2.4%), and systemic lupus erythematosus (1.1%).
When all patients were included in the analysis, those with autoimmune disorders had slightly longer survival times, but these weren’t clinically significant. A subanalysis found a greater difference in survival.
The association appears more pronounced in metastatic cancer. Patients with stage 4 breast cancer and autoimmune disease had a longer mean overall survival (36 months vs. 30 months; hazard ratio, 1.46; P < .0001. Cancer-specific survival: HR, 1.39; P < .0001). Patients with autoimmune disease and stage 1-3 breast cancer had lower overall survival (P < .0001, P < 0.0001, and P = 0.026 respectively), compared with patients without autoimmune disease.
“What we thought was happening is that the lack of increased survival in stages 1 through 3 was hiding the increase in survival among the stage IV patients when looking at the overall cohort,” Dr. Dedousis said.
The retrospective nature of the study makes it impossible to draw any firm conclusions about causation. It could be that patients who have already been diagnosed with an autoimmune disease are more vigilant about going to health checkups. “There are other possible explanations, but the one that’s most interesting to us is that their immune system is involved in fighting the cancer. Our study certainly didn’t prove that, but it’s suggesting that’s a possibility,” Dr. Dedousis said.
He and his coauthors anticipate conducting similar studies in other cancers to see if there are similar relationships. Some preliminary work has already suggested something similar in lung cancer. “I think demonstrating this in a few kinds of cancer goes part of the way towards showing that this is a real biological phenomenon,” he said.
Another research avenue is to examine the immune systems and pathology specimens in patients with both an autoimmune disease and cancer to see if there is a greater immune response within the tumor. If so, that could suggest new immunotherapy strategies.
Another possibility is to look at the specific immune pathways within “protective” autoimmune conditions. “For the sake of argument, if we find a particular autoimmune condition is improving survival across multiple kinds of cancers, we could look at those pathways that are specifically involved in that autoimmune condition. It might help us identify a target for drug development,” Dr. Dedousis said.
Asked why a potential benefit might be more apparent in late-stage disease, he suggested that, in early-stage breast cancer, surgery and other treatments may be so effective that the immune system’s role only rarely makes a difference. It could play a larger role in late-stage disease when there are less effective therapies. It could also be that the immune system doesn’t recognize the cancer until it has spread beyond the regional lymph nodes on its way to metastasizing.
According to the National Cancer Institute, 10%-30% of people with cancer also have an autoimmune disease.
Dr. Dedousis has no relevant financial disclosures.