Cancer in Systemic Lupus Erythematosus: Results from the Systemic Lupus International Collaborating Clinics Inception Cohort

Abstract

Background/Purpose: Published studies of cancer risk in SLE to date have never focussed solely on clinically confirmed, incident patients. Prior studies thus may not reflect the cancer experience of all SLE patients. To fill this knowledge gap, our purpose was to describe cancer incidence in a large inception SLE cohort.

Methods: Patients meeting ACR criteria for new-onset SLE were enrolled across 32 centres. At enrolment and annual assessments, new cancer diagnoses were recorded by the examining physician. Cancers were confirmed by reviewing medical files including pathology reports. Of 1848 patients enrolled across 1999-2011, 1676 had at least one follow-up. Patients were followed until death, last visit, or end of study interval for this analysis(August 2015). Comparison general population cancer rates, weighted according to the age and sex structure of the SLE cohort, were obtained from participating countries.

Results: Mean age at SLE diagnosis was 34.6(standard deviation, SD 13.3). Mean follow-up was 6.85(SD 3.6), for a total of 11,481 patient-years. We observed 46 invasive cancers in 46 subjects. At cancer diagnosis, mean age was 51.6(SD 15.0) and average SLE duration was 4.8(SD 3.1) years. The most common cancer type was breast (n=10), followed by non-melanoma skin cancer (n=8), lung(n=6), prostate(n=5), 4 head and neck (tonsillar, tongue, and 2 oral), cervical(n=2), thyroid(n=2), melanoma(n=2) and one each of non-Hodgkin lymphoma, leukemia, multiple myeloma, , renal carcinoma, gastric carcinoid, thymoma, and dermatofibrosarcoma. Twenty of the 46 patients (43.5%) who developed cancers were current (n=4) or ex-smokers (n=16); five of the six lung cancers were current or ex-smokers. The over-all cancer rate in the SLE population was 4 events per 1000 patient-years(95% CI, 2.9 to 5.4) versus the general population rate of 2.7 events per 1,000 person-years. In young SLE patients(<40), the cancer rate was 2.2 events per 1,000 patient-years(95% CI 1.2, 3.7) which was more than twice that of the general population of this age (1 event per 1,000). The cancer rate in SLE after age 40 was 5 events per 1,000 patient-years, similar to the general population cancer rate for this age group. With very few hematological cancers observed in this inception cohort, the hematological cancer incidence in SLE was 2.6 cancers per 10,000 patient-years (95% CI 0.5, 7.6), which was a non-significant increase above the population rate of 2 per 1,000 person-years. Among other cancer types, only lung cancer was clearly increased versus the general population; the SLE incidence was 5.2 cases per 10,000 person years (95% CI 2-11), versus 1.7 cases per 10,000 person-years in the general population.

Conclusion: The cancer incidence rate in the cohort was 4 events per 1,000. Though higher than general population rates, it is still less than one-half percent per year. Comparisons of cancer in SLE versus the general population must be interpreted with caution, given differences in outcome ascertainment in the two populations. In our analyses, lung cancer was one of the most common cancers. The vast majority of these were smokers, supporting the belief that lung cancer risk in SLE (as in the general population) is largely driven by smoking.