By Shreeya Nanda
Among older aromatase inhibitor (AI)-treated patients with breast cancer, current smokers at treatment initiation have an increased risk of breast cancer events and distant metastases, say Swedish researchers.
As reported in the British Journal of Cancer, they did not find a significant association between smoking and any other treatment modality.
In the subgroup of 309 women aged at least 50 years who were given AI therapy, pretreatment smoking was associated with an elevated risk of breast cancer events (including local or regional recurrence and new breast cancer), distant metastasis and death compared with nonsmokers, with significant adjusted hazard ratios (HRs) of 2.97, 4.19 and 3.52, respectively.
By contrast, among the total study population of 1016 patients, smoking at the pretreatment visit did not significantly increase the risk of breast cancer events during a median follow-up of 5.1 years, although the risk of death from any cause was twofold higher among smokers compared with nonsmokers.
There was no significant correlation between pretreatment smoking and breast cancer events in the subgroup of patients who received chemotherapy, radiotherapy or tamoxifen. This was also the case for AI-treated patients younger than 50 years of age.
Researcher Helena Jernström, from Lund University, and colleagues explain that "[n]icotine and tobacco alkaloids have been shown to inhibit oestrogen synthesis via the aromatase enzyme in vitro", and speculate that "[t]umours that develop in smokers may already be resistant to AIs."
If these findings are replicated, "smoking status should be taken into consideration when selecting endocrine therapy", they write.
However, Jernström and team caution that the smokers and nonsmokers in their study differed with respect to several patient characteristics that may affect prognosis, such as a higher proportion of hormone receptor-negative tumours among smokers. And they say that "[s]moking may also be associated with other patient characteristics that were not assessed in this study such as patterns of physical activity that may influence prognosis."
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Br J Cancer 2016; Advance online publication