Smoking kills -- the phrase holds true for all people, but if you have breast cancer then it kills you even earlier than supposed. To make the statement even more believable, a study published online in the Journal of Clinical Oncology states that if women suffering from breast cancer continue to smoke after diagnosis, they die early than those quitting smoking.

The study was done on more than 20,000 white women between the age of 20 and 79, all diagnosed with breast cancer between 1988 and 2008. The researchers, after six years to diagnosis, contacted more than 4,500 of the women to know about their smoking status.

In the following 12 years, around 6,800 women died and reason for about 2,900 of the deaths was breast cancer. “Smoking causes damage to cells, if you have a cell that's already predisposed to becoming a cancer cell and it gets more DNA damage; it is more likely to become a cancer cell”, said Dr. Veronica Jones, a clinical assistant professor of surgical oncology at City of Hope Cancer Center in Duarte, California.

When the study compared non-smokers to the smoker who left smoking a year before to diagnosis, it concluded that the latter were 25% more likely to die of the disease. They also contracted other diseases such as respiratory cancers or heart disease unlike non-smokers. When 10% women who continued smoking after diagnosis were compared with never smokers, the former were 75% more likely to die of breast cancer. The smokers who stopped smoking after diagnose were 33% less likely to die than those who didn’t stopped.

The women who stop smoking have better results. A breast cancer patient may have complication as smoking could affect tumor growth, according to study leader Michael Passarelli, a cancer epidemiologist at the University of California, San Francisco.