There are many causes of breast pain, including acute mastitis, cystic breast hyperplasia and breast cancer.
Acute mastitis is common in women who are breastfeeding, cystic hyperplasia is common in women aged 30 to 50 years, and a small percentage of breast cancer patients may present with mild vague or dull pains.
Of course some men may also have breast pain associated with endocrine disorders such as estrogen use, hyperadrenocorticism, and cirrhosis of the liver.