In this nationally representative US survey-based study of self-reported cancer prevalence in adults, more than 40% of men and women reported a history of cigarette smoking, with 14.6% of surveyed people reporting smoking e-cigarette smoking. These are consistent with estimates of US adults that 42.5% have a history of cigarette smoking and 14.9% have a history of e-cigarette smoking [25–26]. Unadjusted comparisons demonstrated that individuals with e-cigarette smoking history compared to those with no e-cigarette smoking history were significantly younger at BCa diagnosis. Cigarette, cigar, and pipe smokers had a significantly higher rate of BCa than never smokers. Cigarette, e-cigarette, and pipe smokers had a significantly higher rate of LCa than never smokers. Sensitivity analysis of a multivariable logistic regression for never smoker patients and those with an exclusive history of cigarette or e-cigarette smoking showed that a history of exclusive cigarette smoking was associated with an increased risk of developing LCa and BCa, but a history of exclusive e-cigarette smoking was associated with an increased risk of LCa. These data suggest that e-cigarette smoking might be associated with an increased risk to develop LCa.
Traditional tobacco smoking is an established risk factor for many cancers including breast, lung, bladder, liver, colorectal, and head and neck cancers [3–5]. Because of its relatively recent introduction, not much is known about the effects of e-cigarette smoking and other electronic nicotine delivery system usage on various cancer diagnoses. Studies have found certain carcinogens to be less prevalent in e-cigarette smoking products and e-cigarette smoking users [13–14, 18, 27]. In contrast, others have found that e-cigarette smoking vapor can potentially damage DNA, cause point mutations in genes, and contain heavy metals and other carcinogens potentially raising cancer risk [13–18]. Of note, there are hundreds of different flavors for e-cigarette smoking products, some of which have been found to pose potential inhalation toxicity (e.g., benzyl alcohol, formaldehyde, benzaldehyde, vanillin, tobacco-specific nitrosamines (NNN and NNK), and other toxicants) or induce oxidative stress, inflammation, epithelial barrier dysfunction, and DNA damage in lung cells [10, 18, 28–29]. Furthermore, some reports add that dual use of cigarette smoking and e-cigarette smoking decreases cigarette smoking intake, but total nicotine use and dependence increases, consequently increasing carcinogen exposure and making cessation efforts potentially less effective [30].
LCa is both the most common cancer (11.6%) and the most common cause of cancer death (18.4%) worldwide, with tobacco smoking responsible for upwards of 85% of LCa cases [4, 31]. As e-cigarette smoking products increase the chance of smoking tobacco in the future [21–22], and are introducers of inhaled toxicants themselves [13–18, 28–29], they may be strong drivers of LCa risk. In contrast, while BCa is not as common a cancer (3.0%) or as common a cause of cancer death (2.1%), smoking is the most common risk factor for the development of BCa [5, 31]. Similar bladder carcinogens found in the urine of tobacco users have been found in the urine of e-cigarette smoking users, raising the possibility that e-cigarette smoking could increase the risk for BCa [27, 32]. Exposure time is important in the development of BCa [5]. E-cigarette smoking products have been shown to raise the risk of cigarette smoking usage and are increasingly used by younger persons and never smokers [20–22]. It is therefore possible that BCa risk could be high for e-cigarette smoking users, making them more prone to develop BCa at a younger age, as our data have shown.
This is the only study we are aware of that has looked at the risk of specific cancers for e-cigarette smoking compared to other smoking modalities. Most studies on e-cigarette smoking have thus far focused on the toxicological and carcinogenic properties of the various components in e-cigarettes, their association with quitting traditional-smoking modalities such as cigarette smoking, subsequent cigarette smoking use for e-cigarette smoking users, and risks to adolescents. This is unsurprising as e-cigarette smoking products are relatively novel and the cumulative effects of e-cigarette smoking, with regards to cancer diagnosis, take years to manifest.
The current study has several limitations. Firstly, the data is retrospective consisting of inherent biases, with possible inaccurate or unreported data entry. As a survey-based study, it is prone to recall bias among responding subjects. Additionally, while this database accounts for many significant socio-economical and clinical factors, direct ascertainment of other relevant clinical information is lacking, such as known malignancy risk factors, including family history, personal genetic risk factors, detailed history of medical comorbidities, diet, and occupational history. Another important limitation is the lack of data on the timing of smoking, and when exactly did it occur before the cancer diagnosis (if a cancer diagnosis exists). Importantly, all analyses were based on self-reported outcomes without confirmation of type, timing of cancer diagnosis, and cancer grade. Lastly, we had no socioeconomical data available to include in our analyses.
Despite these limitations, our study represents a large and nationally representative cohort of US men and women providing recent self-reported cancer prevalence and history of various smoking modalities, including e-cigarette smoking. These data suggest that, compared with never smokers, and after adjusting for all histories of other smoking modalities, a history of e-cigarette smoking by itself is independently associated with an increased risk of LCa and BCa development. Despite being marketed as a smoking cessation aid and as a safer alternative to tobacco smoking, e-cigarette smoking might be associated with an increased risk of some smoking related cancers. Our data warrant additional studies to examine the public health effects of these relatively novel and unregulated smoking products, which are more common among younger individuals, potentially putting them at an increased risk.