The researchers, reporting in the Journal of Clinical Oncology, came to that conclusion after finding women with invasive lobular carcinoma did not respond to chemotherapy yet had better survival rates than those suffering from the most common form of breast cancer, invasive ductile carcinoma.

Massimo Cristofanilli, the study's author and an associate professor, said the finding was "striking," particularly when compared with women who suffer the ductile form of cancer.

"This study suggests women with invasive lobular carcinoma have a different kind of disease," Cristofanilli said. "Before this study, I don't think anyone realized the disease should be treated differently."

The University of Texas researcher said doctors also should change the way they talk about progress to women who have lobular cancer who respond poorly to chemotherapy.

Lobular carcinoma, the No. 2 form of breast cancer behind ductile carcinoma, accounts for 5 to 15 percent of all breast cancer cases, researchers said.

Results were based on examining histories of about 1,000 women.