Background: High incidence of breast cancer and its fatal effect has reached an alarming stage across the globe, including the third world countries. Many factors have been reported to be associated with the development of breast cancer but detailed structural and functional information is missing. CA 15-3 is one of the known potential tumor marker of breast cancer; however little is known about structure and functional site of this protein. Present study aims to investigate the functional role of CA 15-3 in breast cancer, especially in development and metastasis. Material and Methods: Hundred female breast cancer patients confirmed by histopathological reports were included in the study. Their physiological characters were recorded in a performa. Enzyme linked immunosorbent assay (ELISA) technique was used to estimate serum CA 15-3 level. Immunohistochemistry was done for estrogen (ER), progesterone (PR) and Her2/neu receptors expression. Results: The study revealed the details of physiological characteristics of female breast cancer. Mean age was $37.72{pm}5.99$ and $55.05{pm}7.28$ years and serum CA 15-3 (MUC1) level was $60.47{pm}8.59$ and $63.17{pm}4.58$ U/ml in pre and post-menopause respectively, and both groups of women had sedentary life style. Their receptor status especially of progesterone, estrogen and HER-2/neu were positive in 50% of premenopausal women and 65% of postmenopausal women. Conclusion: There are multiple physiological factors promoting breast cancer. High serum CA 15-3 level and hormonal imbalance of ER, PR and Her2/neu appears to be the main cause of breast cancer. It may be possible that the functional sites of these proteins may be altered which may increase the chances of metastasis in breast cancer.