IT'S A MYTH
But on the other hand, breast reduction surgery reduces the risk of cancer in approximately the proportion of tissue removed. The explanation here is quite pure: by removing the gland tissue, plastic surgeons also remove the potentially dangerous areas that are present in it. This reduces the risk. It is curious that, contrary to popular belief, the number of operations to reduce the breast is quite comparable with the number of operations to increase it. This is a fairly popular procedure.
Breast size doesn't affect the risk of getting cancer. However, small breast size facilitates cancer screening: the chance of skipping cancer in the large mammary gland is higher.