The breasts connect to the feminine principle of nurturing and the maternal instincts. They are also connected to sexuality and eroticism for many.
A mastectomy is a radical response to the presence of cancer in the form of complete surgical removal of one or both breasts. As a symbol, such an act is reflecting a deep loss of connection to these powerful feminine forces. There may be a literal connotation to the dream if you or someone you know is going through a waking-life experience of facing breast cancer.
(See Also: Breasts.)
[1]1. One feels less than attractive as a female.
2. If diagnosed with cancer, worry over the condition.
[2]