Searching for evidence on the relationship between tuberculosis and lung cancer in Africa: protocol for a scoping review

Background Lung cancer is one of the most common malignancies, with an incidence in 2022 of 23.6/100.000 globally and 6.3/100.000 individuals in Africa.1 It is also responsible for mortality of 16.8/100.000 globally and 5.8/100.000 individuals in Africa and is the cancer with the highest mortality compared to all types of cancer1 Smoking has been considered an important risk factor for lung cancer.2,3 However, environmental factors such as air pollution, nutrition, occupational exposure, and family history of cancer are also related.4,5 In recent decades, with advances in molecular diagnostics, genetic and inflammatory factors that contribute to carcinogenesis have been identified as potential risk factors for the development of lung cancer.4–6 Pulmonary tuberculosis is one of the most prevalent infectious diseases in middle- and low-income countries. More than 10 million individuals are affected by the disease each year, with an estimated 155 million tuberculosis survivors worldwide by 2020.7 Survivors of tuberculosis have a higher risk of all-cause mortality8 and reduced life expectancy,9 probably due in part to the higher risk of non-communicable diseases following tuberculosis.10,11 Several studies have shown that previous inflammatory lung diseases such as tuberculosis can increase the risk of lung cancer, independently of smoking.12–15 Thus, pulmonary tuberculosis (PTB) infection can influence the pathogenesis of lung cancer with or without smoking. Four systematic reviews, all published in 2022, addressed this relationship. The first included 33 studies with 982,797 participants from countries in Asia, Europe and North America (all high- and middle-income countries), concluded that a diagnosis of PTB at a young age was a risk factor for lung cancer, regardless of underlying disease or smoking history. This trend was more evident in patients from countries with a high tuberculosis burden.16 The second, which included 29 cohort and 44 case-control studies from Asia, North America and Europe documented an association between tuberculosis and lung cancer occurrence, particularly in, but no limited to, the first 2 years after tuberculosis diagnosis.17 The third review included 17 studies also from high- and middle-income countries, showed that tuberculosis patients had an increased risk of lung and non-lung cancer.18 The risk was highest in the first year after the diagnosis of tuberculosis but seemed to persist for years after the end of tuberculosis treatment.18 A fourth review was about the comparison of clinical and imaging features between PTB with lung cancer and simple PTB summarized the similarities and differences in clinical symptoms and imaging characteristics between patients with PTB and lung cancer and patients with PTB alone, where the authors suggest that we should be alert to the occurrence of lung cancer in patients with PTB relapse.19 None of these reviews included studies from middle- or low-income African countries, which are the countries with the highest prevalence of tuberculosis. It is unclear if no study about PTB and lung cancer was conducted in these countries, or if studies were simply not captured in the literature search strategies. We, therefore, set out to carry out this scoping review to map the body of evidence produced in African countries about the relationship between lung cancer and PTB.