As per a worldwide analysis in 2018, an estimated 2·2 million infection-attributable cancer cases were diagnosed. Helicobacter pylori, human papillomavirus, hepatitis B virus and hepatitis C virus were the primary causes of infections. Of the regions analysed, China accounted for one-third of worldwide cancer cases attributable to infection.

Infections with certain viruses, bacteria, and parasites are strong risk factors for specific cancers; hence, it is important to monitor the contribution of infectious pathogens to the worldwide cancer burden. A worldwide analysis based on the GLOBOCAN cancer database was conducted to estimate the number of infection-associated cancers diagnosed.

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13% of all cancer cases were caused due to infections

In 2018, about 2·2 million cancer cases, which is 13% of global cancer incidence, were attributable to infection. The age-standardised incidence rates (ASIR) of infection-attributable cancers varied considerably by region, with the highest rates observed in eastern Asia and sub-Saharan Africa.

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Infectious pathogens which were primarily responsible- H. pylori, HPV, HBV and HCV

Helicobacter pylori, high-risk human papillomavirus (HPV), hepatitis B virus (HBV), and hepatitis C virus (HCV) were responsible for more than 90% of infection-related cancers worldwide.

• H. pylori caused 8,10,000 new cases, mainly non-cardia gastric adenocarcinoma
• HPV was responsible for 6,90,000 new cases mainly cervix uteri carcinoma
• HBV contributed 3,60,000 new cases
• HCV caused 1,60,000 new cases mainly of hepatocellular carcinoma
• Epstein-Barr virus, human T-cell lymphotropic virus type 1 (HTLV-1), human herpesvirus type 8 (HHV8; also known as Kaposi sarcoma herpesvirus), and parasitic infections caused the remaining 2,10,000 new cases

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The relative contribution of the four main infectious pathogens to cancer incidence demonstrated great regional variability

The incidence of infection-attributable cancer was observed to be highest in eastern Asia (37·9 cases per 100 000 person-years) and sub-Saharan Africa (33·1), and lowest in northern Europe (13·6) and western Asia. H. pylori (17·6 cases per 100 000 person-years) and HBV (10·5 cases per 1,00,000 person-years) were responsible for the highest burden of infection-attributable cancers in eastern Asia.

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China accounted for 35% of the 2·2 million new infection-attributable cases worldwide

In 2018, China alone accounted for 7,80,000 cases of infection-attributable cancer, which represents 35% of the 2·2 million new cases worldwide. This includes 69% of all cancers attributable to HBV and 42% due to  H. pylori.

Very high incidence of cancer caused by H. pylori infection was also observed in South Korea and Japan, with high incidence of HBV-attributable cancer additionally seen in South Korea.

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1,90,000 new infection-attributable cases were diagnosed in India

The table below shows the estimated numbers of infection-attributable cancer cases in 2018 in India. In India a total of 1,90,000 cases were diagnosed; of these the highest number of cases (45,000) were due to H. pylori. The remaining 1,20,000 cases were due to HPV, 9,000 due to HBV and 4,700 due to HCV infection.

Pathogen	ASIR	Number of attributable cases
H. pylori	3·5	45,000
HPV	9·0	1,20,000
Hep B	0·7	9,000
Hep C	0·4	4,700
All infectious pathogens	14·3	1,90,000

• Data are ASIR per 1,00000 person-years   (ASIR: Age-standardised incidence rate)

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H. pylori is the most important infectious cause of cancer worldwide

H. pylori is the leading cause for infection-attributable cancer. In 2018, around 8,10,000 cases of cancer were reported due to H. pylori. The reasons responsible for the high incidence of stomach cancer related to H. pylori in the high-risk areas (eastern Asia, Latin America, and eastern Europe) includes:

• High rate of transmission
• Aggressive strains expressing virulence factors
• Environmental co-factors

As per the authors, while treatment strategies for H. pylori can help reduce the incidence of gastric cancer; the issues of large-scale antibiotic use on the human microbiome and the optimal drug combination in areas of increasing antibiotic resistance are matters which need definite solution.

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The cancer burden attributed to HPV showed the clearest relationship with country income level

Of the cancers caused by HPV, 80% are cervical cancer. For cancer due to HP, a clear inverse association was observed between incidence rates and income level, increasing from 6·9 cases per 1,00,000 person-years in high-income and upper-middle income countries to 9·2 in lower-middle-income and 16·1 in low-income countries. This trend is attributed to the availability of cervical cancer screening which has led to significant decreases in incidence and mortality of cervical cancer in high-income settings.

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Burden of infection-attributable cancer stratified by sex

The overall burden of infection-attributable cancer was shared equally by men and women, but the spectrum of infectious pathogens and cancer varied by sex. In all regions, HPV-attributable cancer predominated in women, whereas cancer attributable to other infections was more common in men than in women. Around 90% (n=620 000) of the 690 000 cases HPV-attributable cancers worldwide were found in women. In men, non-cardia gastric cancer due to H pylori accounted for the highest number of cases (490 000 cases).

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Reference: de Martel C, Georges D, Bray F, et al. Global burden of cancer attributable to infections in 2018: a worldwide incidence analysis. Lancet Glob Health. 2020 Feb;8(2):e180-e190.