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Cigarette smoking and risk of second primary cancer: a systematic review and meta-analysis

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Title : Cigarette smoking and risk of second primary cancer: a systematic review and meta-analysis
Author: Zhi Jing Phua a, Robert J. MacInnis a,b, Harindra Jayasekara a,b,c,*
Publication: Cancer Epidemiology
Publisher: Elsevier Inc
Year: 2022
Language: English
Pages: 17
Format: PDF
File size: 1,077 KB
DOI: 10.1016/j.canep.2022.102160
CBID: CBR219

Categories: Researches, Medical Researches Tags: Cigarette smoking; Meta-analysis; Second primary cancer; Systematic review., Medical Researches

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Abstract

Approximately 5% of the population are living with a diagnosis of cancer. Recent improvements in survival following a diagnosis of cancer have led to an increase in second primary cancers (SPCs) worldwide. Their aetiology remains largely unknown with a large proportion believed to be related to modifiable lifestyle factors. We conducted a systematic review and meta-analysis of published data that evaluated an association between cigarette smoking and risk of SPC. Studies were identified by searching Medline, Web of Science, CINAHL (Cumulative Index to Nursing and Allied Health Literature) and Scopus databases through March 2021 using broad search criteria. A meta-analysis was performed to derive pooled relative risks (RRs) for SPC defined a priori as smoking-related based on current evidence (lung, upper aero-digestive tract, stomach, pancreas, colorectum, liver, kidney, ureter, bladder and acute myeloid leukaemia). Eleven cohort studies and ten case-control studies met the eligibility criteria for review. There was marked heterogeneity in methods used in terms of classification and timing of smoking, confounders adjusted for and duration of follow-up across the studies. Nine cohort and seven case-control studies classified smoking habits prior to diagnosis of first cancer while the remaining studies classified post-first cancer smoking habits. In a meta-analysis using six studies, an increased risk of smoking-related SPC was observed for both former (RR=1.42; 95% confidence interval (CI) 1.20–1.67) and current smoking (RR=2.76; 95% CI 2.29–3.33), compared with never smoking. The pooled RRs changed only slightly when studies which measured post-first cancer smoking were excluded. A two-fold increase in risk was observed for ever smoking compared with never smoking. In conclusion, there was evidence that smoking might increase the risk of SPC in cancer survivors. For better informed cancer survivorship practice guidelines, more studies are needed particularly of post-cancer smoking and for cancers not known to be caused by smoking.

Highlights

• Cigarette smoking is the largest preventable risk factor for developing cancer.
• Incidence of second cancers in cancer survivors is rising worldwide.
• Published evidence on smoking and second cancer risk was synthesised.
• Smoking increased subsequent cancer risk in cancer survivors by over two-fold.
• Cessation of smoking is important in cancer survivorship.

1 Introduction

pproximately 5% of the population in high-income countries are living with a diagnosis of cancer , and this number is expected to grow rapidly in the next decade . A combination of early detection, quality supportive care and effective treatment has led to enhanced survival following a diagnosis of cancer in recent decades. Nearly 70% of all adult cancer survivors live at least 5 years beyond the diagnosis of their first cancer and 64% are aged 64 years or over . A significant consequence of the rapidly growing population of cancer survivors is the substantial rise in the incidence of second primary cancer (SPC), defined as a new primary cancer that is not a recurrence or a metastatic deposit of the initial lesion. SPCs are more fatal and have lower survival rates than first primary cancers, even in high-income countries . It has been estimated that the 5-year second cancer-specific mortality is approximately twice as high as the 5-year first cancer-specific mortality in the US general population and in Australia .

The aetiology of SPC remains largely unknown with a small fraction attributed to initial cancer treatment with most believed to be caused by underlying genetic and/or lifestyle factors . Less than 10% of solid SPCs in adults are caused by radiotherapy, the main treatment modality known to increase cancer risk, and chemotherapy and targeted drug therapies cause even fewer . Although assuring the long-term health of cancer survivors is a priority, existing prevention guidelines only target first cancers, highlighting the lack of targeted prevention guidelines for SPC . In this systematic review, we aimed to collate and summarise published observational data on the association between pre- and post-diagnosis cigarette smoking, which is a leading modifiable cause of cancer worldwide , and risk of SPC.