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Occasional inversion of the nipple is fairly common after the menopause. this is because the low estrogen levels in the blood lead to loss of breast tissue and fat from the breasts. As the results, the skin of the nipple lose support, become less firm and may get inverted.
Being manually able to revert the nipple is a good sign since it indicates that there is no abnormal growth pulling the the nipple. In breast cancer, abnormal cells tend to pull and cause inversion of the nipple - in this case, the nipple cannot be reverted back to the original position.
I believe that your nipple inversion is due to menopausal changes rather than breast cancer.