Lifetime risk of malignancy in polymyalgia rheumatica: a population-based matched cohort study from southern Norway.

Abstract

Prior studies examining the malignancy risk in polymyalgia rheumatica (PMR) have reported conflicting results, with some indicating an increased risk within 6-12 months after diagnosis. This study assessed malignancy risk over the lifetime and at different follow-up horizons in a population-based inception cohort of PMR patients. All incident PMR cases (n = 296) in Aust-Agder County, Norway, between 1987-1997 were enrolled at diagnosis in a prospective, population-based study. Diagnosis was ascertained clinically by rheumatologists, with all cases fulfilling Bird`s criteria. Each PMR case was matched by age, sex, and residency to 15 random comparators (n = 4,440). Cancer incidence data were obtained from the Cancer Registry of Norway. Participants were followed until first cancer diagnosis, death or December 31, 2024. Malignancy risk was estimated using Cox regression stratified on matched groups. The mean age at PMR diagnosis was 72 years, 67.6% were female, and 95.6% were deceased by December 31, 2024. Median follow-up was 14.1 years in PMR patients and 13.9 years among comparators. Following the index date, 70 PMR patients (23.6%) and 1,104 comparators (24.9%) developed malignancy. PMR was not associated with an increased malignancy risk (Hazard ratio 0.94, 95% confidence interval: 0.73, 1.21), nor with significant excess risk in separate analyses by cancer type or by time since diagnosis. In this long-term follow-up of a population-based PMR inception cohort, we found no excess malignancy risk at any time from PMR diagnosis through the end of life. These findings reinforce the notion that PMR is not a cancer-associated disease.