The greatest reduction in risk was seen in invasive oestrogen receptor-positive breast cancer ( HR 0.66 [ 95 % CI 0.54-0 .81 ] , p < 0.0001 ) and ductal carcinoma in situ ( 0.65 [ 0.43-1 .00 ] , p = 0.05 ) , but no effect was noted for invasive oestrogen receptor-negative breast cancer ( HR 1.05 [ 95 % CI 0.71-1 .57 ] , p = 0.8 ) .