Respiratory tract infections in the pathway to multiple myeloma: a population-based study in Scandinavia.

Encounter with infectious antigens has been proposed to initiate the cascade of events associated with progression from premalignancy (monoclonal gammopathy of undetermined significance, MGUS) to multiple myeloma (MM). We conducted a population-based case-control study to evaluate risk of developing MM associated with a personal history of various respiratory tracts infections occurring >1 year prior to MM. Inpatient (1977-1997) and outpatient (1994-1997) diagnoses were obtained for all MM patients (n=4,476) diagnosed in Denmark (1977-1997) and 16,727 matched controls. A personal history of pneumonia was associated with a 1.6-fold (95%CI 1.3-2.0) increased risk of MM; the elevated risk was restricted to 1-4.99 years prior to the diagnosis of MM (OR=1.7,95%CI 1.3-2.2). Individuals with two and three or more previous episodes of pneumonia had a 1.7-fold (95%CI 1.0-3.0; p=0.05) and a 1.5-fold (95%CI 0.6-3.9) elevated MM risk, respectively. Pneumonia could be a trigger to the development of MM or a manifestation of immune disturbances in late-stage MGUS.