Swedish researchers have identified a protein commonly found in connective tissue that contributes to the development as well as spread of breast cancer.

Cartilage Oligomeric Matrix Protein (COMP) is a protein that has been found in cartilage -- a connective tissue found in many areas of the body including joints between bones of elbows, knees and ankles.

"We did not expect to find COMP in connection with breast cancer, and we were also surprised by the strong effect it had on the development of breast cancer in mice," said Emelie Englund, researcher at Lund University in Sweden.

The findings revealed that women, who had higher levels of COMP, experienced an increase in the spread of breast cancer, to the surrounding tissues and also showed an increase in the mortality rate.

COMP not only contributed to a more rapid growth of the primary tumour, but also to the formation of metastases.

Further, COMP affects the cell metabolism and makes the breast environment less favourable to healthy cells.

It makes the cancer cells more resistant to natural cell death.

"We saw a clear association between high levels of COMP and a worse breast cancer prognosis", explained Anna Blom, professor, in the paper published in the journal Oncogene.

Various amounts of COMP were found in both the tumours and the surrounding tissue, but never in healthy breast tissue.

With more research, COMP has the potential of becoming an indicator of aggressive breast cancer, and thereby providing early and valuable information before deciding on an appropriate treatment, the researchers indicated.

The results are based on a clinical study of breast tissue from a little more than 600 women with breast cancer.