WASHINGTON (AFP) - Nicotine could play a role in the development and growth of tumors in breast cancer, according to a new study published Wednesday. Researchers studied for the first time the effects of nicotine on mammary cells and concluded the chemical found in cigarette smoke could contribute to cancerous growth. "Although numerous studies indicate the role of nicotine exposure in tumor promotion, little is known about the effect of nicotine on breast tumor development," said lead author of the study Chang Yan Chen, from the research team at the Beth Israel Deaconess Medical Center at Harvard University, Massachusetts. Through a series of tests, researchers found that both breast epithelial cells " protective cell tissue that lines organs throughout the body " and cancerous cells have nicotine receptors (nAChR), which have the potential to increase cell growth and migration in the presence of nicotine. "The best known role of nAChR is in the nerve system," Chen said, in the study published in Cancer Research, a journal of the American Association for Cancer Research. But scientists know little about the function of nicotine receptors in cells and tissues outside the nerve system, for example in mammary cells. The research team found through tests on live animal subjects that nicotine, in its interaction with normal cell growth, contributes to tumor growth in mammary cells. Further studies are necessary to strengthen the finds, said Chen. "At this point we can only suggest that nicotine potentiates the growth-related process," she said.