Medical student Department of Clinical Epidemiology, Deparment of Clinical Medicine, Aarhus University and Aarhus University Hospital, Denmark, Denmark
Background: Immune dysregulation has been associated with cancer progression. Epidemiological studies suggest shorter disease-free survival among breast cancer survivors who have increased levels of circulating inflammatory markers. Yet, the association between infection and risk of breast cancer recurrence is not fully understood.
Objectives: To examine the influence of infection on the risk of breast cancer recurrence.
Methods: We conducted a Danish nationwide case-control study of women diagnosed with non-metastatic breast cancer during 1987-2004. By linking individual-level data from registries we obtained information on breast cancer, recurrence, antimicrobial prescriptions, and hospitalization for infection. Recurrences diagnosed within the first 10 years after primary diagnosis were ascertained from the Danish Breast Cancer Group clinical database, while recurrences diagnosed >10 years after primary diagnosis were identified via a validated algorithm. We compared use of antimicrobial (antibiotic, antiviral, antifungal) drugs and diagnostic codes for infection as combined and separate measures of infection among women diagnosed with recurrent breast cancer (cases) to that of recurrence-free women (controls). Cases and controls were matched on age and date of breast cancer surgery. Using conditional logistic regression, we estimated odds ratios (OR) and 95% confidence intervals (CIs) for recurrent breast cancer associated with antimicrobial use and hospitalization for infection. We evaluated type of infection, cumulative exposure based on number of prescriptions/hospitalizations, and stratified the models according to exposure periods to evaluate the role of time between prescription/hospitalization and recurrence.
Results: Overall, 3,770 (70.0%) cases and 18,603 (68.8%) controls had used antimicrobial drugs and 1,304 (11.5%) cases and 6,453 (11.4%) controls had been hospitalized for infection. Use of antimicrobials/hospitalization for infection was not associated with increased risk of recurrence (OR 1.06 95% CI 0.99-1.14) compared to no use of antimicrobials/no hospitalization. We did not observe higher risk of recurrence with increasing number of prescriptions/hospitalizations, which contradicts a causal effect. Nor did time from last infection to recurrence influence risk of recurrence. Stratified analyses showed a slightly positive association between skin infections and risk of recurrence (OR 1.11 95% CI 0.99-1.25).
Conclusions: We found no clear evidence to support an association between infections and risk of breast cancer recurrence, which is encouraging for breast cancer survivors who suffer from infections.
