Women who continue to smoke after being diagnosed with breast cancer are nearly twice as likely as those who never smoked to die of their disease, a recent study from the University of California, San Francisco concluded.1

This study—the largest on this topic to date—also found that women who quit smoking after diagnosis lowered their mortality from both breast and respiratory cancers.

“Our study reinforces the importance of cigarette smoking cessation for women with breast cancer,” Michael N. Passarelli, PhD, of the Department of Epidemiology and Biostatistics at the University of California, San Francisco, and colleagues wrote in the Journal of Clinical Oncology.

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Acknowledging that “very little is known about women who continue to smoke” after a diagnosis of breast cancer (about 10%), the team analyzed data from the Collaborative Breast Cancer Study. These data included 20 691 women in New Hampshire, Massachusetts, and Wisconsin diagnosed with incident invasive breast cancer from 1988 to 2008 and a subset of 4562 who participated in the Collaborative Women’s Longevity Study.

They found that across a 12-year median, 6778 women died, including 2894 from breast cancer and 1394 from cardiovascular disease.

Women who were active smokers 1 year prior to their breast cancer diagnosis were more likely than never smokers to die of their disease (HR, 1.25) and to die of respiratory cancer, including neoplasms of the nasopharynx, larynx, trachea, bronchus, lung, pleura, and intrathoracic organs (HR, 14.48), as well as other respiratory disease (HR, 6.02) and cardiovascular disease (HR, 2.08).

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“The higher relative risks of death as a result of breast cancer were observed among long-term smokers (≥ 30 years), high–pack-year smokers (≥ 30 pack years), and former smokers having quit fewer than 5 years before breast cancer diagnosis,” the article stated.