A new study has quantified cancer risk factors in patients with systemic lupus erythematosus, including smoking and the use of certain medications.
“As expected, older age was associated with cancer overall, as well as with the most common cancer subtypes,” wrote Sasha Bernatsky, MD, PhD, of McGill University, Montreal, and coauthors. The study was published in Arthritis Care & Research.
To determine the risk of cancer in people with clinically confirmed incident systemic lupus erythematosus (SLE), the researchers analyzed data from 1,668 newly diagnosed lupus patients with at least one follow-up visit. All patients were enrolled in the Systemic Lupus International Collaborating Clinics inception cohort from across 33 different centers in North America, Europe, and Asia. A total of 89% (n = 1,480) were women, and 49% (n = 824) were white. The average follow-up period was 9 years.
Of the 1,668 SLE patients, 65 developed some type of cancer. The cancers included 15 breast;, 10 nonmelanoma skin; 7 lung; 6 hematologic, 6 prostate; 5 melanoma; 3 cervical; 3 renal; 2 gastric; 2 head and neck; 2 thyroid; and 1 rectal, sarcoma, thymoma, or uterine. No patient had more than one type, and the mean age of the cancer patients at time of SLE diagnosis was 45.6 (standard deviation, 14.5).
Almost half of the 65 cancers occurred in past or current smokers, including all of the lung cancers, while only 33% of patients without cancers smoked prior to baseline. After univariate analysis, characteristics associated with a higher risk of all cancers included older age at SLE diagnosis (adjusted hazard ratio, 1.05; 95% confidence interval, 1.03-1.06), White race/ethnicity (aHR 1.34; 95% CI, 0.76-2.37), and smoking (aHR 1.21; 95% CI, 0.73-2.01).
After multivariate analysis, the two characteristics most associated with increased cancer risk were older age at SLE diagnosis and being male. The analyses also confirmed that older age was a risk factor for breast cancer (aHR 1.06; 95% CI, 1.02-1.10) and nonmelanoma skin cancer (aHR, 1.06; 95% CI, 1.02-1.11), while use of antimalarial drugs was associated with a lower risk of both breast (aHR, 0.28; 95% CI, 0.09-0.90) and nonmelanoma skin (aHR, 0.23; 95% CI, 0.05-0.95) cancers. For lung cancer, the highest risk factor was smoking 15 or more cigarettes a day (aHR, 6.64; 95% CI, 1.43-30.9); for hematologic cancers, it was being in the top quartile of SLE disease activity (aHR, 7.14; 95% CI, 1.13-45.3).
The authors acknowledged their study’s limitations, including the small number of cancers overall and purposefully not comparing cancer risk in SLE patients with risk in the general population. Although their methods – “physicians recording events at annual visits, confirmed by review of charts” – were recognized as very suitable for the current analysis, they noted that a broader comparison would “potentially be problematic due to differential misclassification error” in cancer registry data.
Two of the study’s authors reported potential conflicts of interest, including receiving grants and consulting and personal fees from various pharmaceutical companies. No other potential conflicts were reported.
SOURCE: Bernatsky S et al. Arthritis Care Res. 2020 Aug 19. doi: 10.1002/acr.24425.