A POPULATION-BASED CASE-CONTROL STUDY OF CANINE MAMMARY-TUMORS AND CLINICAL USE OF MEDROXYPROGESTERONE ACETATE

We investigated whether or not an association could be found between m ammary rumours and prior clinical use of medroxyprogesterone acetate ( MPA) in bitches. A population-based retrospective age-matched case-con trol study was designed based on interviews with the owners of the bit ches. The proportion of bitches with diagnosed mammary tumours (group MT+, n = 98) that had received progestin injections was compared with the proportion in a control group without mammary rumours (group MT-, n = 98). In the case group 39%, and in the control group 21% of the bi tches had been treated with MPA. A significantly higher number of bitc hes with mammary rumours had been exposed to progestins, compared with the control group without mammary tumours (odds ratio = 2.32, Chi-squ are = 7.01, p = 0.008). Bitches treated clinically with low doses of M PA to avoid oestrus were at a greater risk of developing mammary tumou rs, the majority of which were histologically malignant (91%).