Nested case-control study of the effects of nonsteroidal anti-inflammatorydrugs on breast cancer risk and stage

We carried out a nested case-control study to measure the rate ratio (RR) f or invasive female breast cancer in relation to nonsteroidal anti-inflammat ory drug (NSAID) use. The source population consisted of the female benefic iaries of the Saskatchewan Prescription Drug Plan from 1981 to 1995 with no history of cancer since 1970. Four controls/case, matched on age and sampl ing time, were randomly selected. Dispensing rates during successive time p eriods characterized NSAID exposure. RRs associated with exposure during ea ch period were adjusted for exposure during the others. Confounding by othe r determinants was studied in analyses adjusted with data obtained by inter viewing samples of subjects accrued from mid-1991 to mid-1995. We accrued 5 882 cases and 23 517 controls. Increasing NSAID exposure 2-5 years precedin g diagnosis was associated with a trend towards a decreasing RR (P-trend = 0.003); for the highest exposure level RR = 0.76, 95% confidence interval 0 .63-0.92. This protective effect could not be attributed to confounding by other determinants. In analyses involving only the cases, NSAID exposure 2- 5 and 6-10 years preceding diagnosis was associated with significantly redu ced risks of presenting with a large tumour (> 5 cm diameter) or distant me tastasis, but not regional lymph node metastasis. The use of NSAIDs may ret ard the growth of breast cancers and prevent distant metastasis. (C) 2000 C ancer Research Campaign.