Importance of Smoking Cessation to Reduce Breast Cancer Mortality

VOLUME NUMBER APRIL J OURNAL OF C LINICAL O NCOLOGY E D I T O R I A L Importance of Smoking Cessation to Reduce Breast Cancer Mortality Barbara A. Parker and John P. Pierce, University of California, San Diego, La Jolla, CA See accompanying article on page 1315 In 2014, the Surgeon General concluded that, among breast cancer survivors, persistent cigarette smoking was causally asso- ciated with adverse health outcomes, although the evidence for an association with breast cancer recurrence was only suggestive. 1 Published associations with recurrence could not rule out potential confounders. For example, smokers were known to have lower rates of mammographic screening, which suggested that they might be diagnosed with higher-stage disease, which could explain a worse prognosis. 1 Smokers were more likely to have developed comorbidities that affected longevity; some also received less than recommended doses of cancer treatments, including adjuvant endo- crine therapies for patients with hormone receptor–positive disease. 1 Recently, reports from breast cancer–speciﬁc longitudinal studies have addressed these concerns. One issue that has limited the ability to detect a relationship between smoking and breast cancer prognosis is the low prevalence of ongoing smoking among patients diagnosed with breast cancer. 2 The low prevalence of persistent smoking requires a large sample size of breast cancer survivors to identify moderate risk associations. Two recent stud- ies, each with approximately 3,000 breast cancer survivors, did not have the power to achieve statistical signiﬁcance for an estimated 23% increased risk of breast cancer mortality. 2,3 A lack of power was also a problem for a hospital-based cohort of nearly 6,000 breast cancer survivors, in whom the estimated smoking effect size was 115%. 4 However, when the effect size was considerably larger (eg, 155%), a smaller follow-up study of approximately 2,000 breast cancer survivors reported the effect as statistically signiﬁcant. 5 In the article that accompanies this editorial, a study by Passarelli et al 6 reported results from a well-powered study of 20,691 breast cancer survivors, in which persistent smoking was associated with a statistically signiﬁcant 25% increased risk of breast cancer death after analysis was controlled for stage and multiple risk factors. This is one of a number of recently published studies (with various study designs) to report a statistically sig- niﬁcant association of persistent smoking with breast cancer– speciﬁc outcomes. One study was a cohort of almost 10,000 breast cancer survivors that identiﬁed an effect size of 61%. 7 Two large population-based cohorts have reported an association of smoking with breast cancer mortality: one was a study of 128,000 breast cancer survivors in Florida, which reported an effect size of 115%; 8 the other was a study of . 300,000 Norwegian breast cancer survivors that reported an effect size of 133%. 9 In a large study Journal of Clinical Oncology, Vol 34, No 12 (April 20), 2016: pp 1295-1296 that included . 6,000 patients with hormone receptor–positive breast cancer who had survived for at least 5 years, Nechuta el al 10 noted that, after analysis was adjusted for other risk factors that included non–smoking-related lifestyle measures, persistent smoking was associated with a 130% increase in breast cancer mortality. The consistency of the statistically signiﬁcant associations that link persistent smoking with higher breast cancer mortality across these studies suggests a causal association. The recent study by Passarelli et al 6 observed that patients who quit smoking had a 33% reduction in breast cancer death rate; however, because these patients were a small subsample of those enrolled in the overall study, this result did not reach statistical signiﬁcance. Both the magnitude and the direction of the effect, though, are consistent with other evidence of the beneﬁts of smoking cessation for other cancers. 1 We estimate that up to 20,000 US women will continue smoking after a diagnosis of breast cancer. The evidence described in this editorial suggests that successful promotion of smoking cessation among these patients could lead to a signiﬁcant, additive beneﬁt to the established beneﬁts of adjuvant chemotherapy, 11 adjuvant endocrine therapy, 12 and postmastectomy radiation therapy 13 and that it may be as important as, or more important than, any other survivorship recommendations. Additionally, smok- ing cessation in these patients may mitigate surgical complications 14 and avoid much of the excess risk of secondary lung cancer and heart disease seen in patients with breast cancer who smoke and who undergo curative intent radiation. 15 Reasons why approximately half of medical oncologists have not aggressively promoted smoking cessation 16 include the fol- lowing: unclear evidence of beneﬁt; lack of time; priority of pri- mary treatment; and inadequate training and expertise, especially when patients exhibit high psychological stress and depression. From the study by Passarelli et al, 6 we can calculate that ap- proximately 45% of smokers (352 of 786) at the time of breast cancer diagnosis may successfully quit within 6 years. This ces- sation rate is similar to the 43% reported for smokers diagnosed with cancers strongly related to smoking, such as head, neck, and lung cancers. 17 With this additional evidence of mortality beneﬁt, it is appropriate to revisit the resources necessary for promoting smoking cessation in breast oncology practice and for collecting data in future research studies. It should be possible to increase the cessation rate among patients with breast cancer to 75%. The new National Comprehensive Cancer Network Guidelines for Smoking © 2016 by American Society of Clinical Oncology Downloaded from ascopubs.org by University of California, San Diego on April 28, 2017 from 137.110.224.250 Copyright © 2017 American Society of Clinical Oncology. All rights reserved.