What is the second biggest cause of lung cancer in the world? by Connie b. Dellobuono

Answer by Connie b. Dellobuono:

Tobacco use according to WHO (1). (2) Carcinogens (environment: physical,chemical,biological)
Cancers figure among the leading causes of morbidity and mortality worldwide, with approximately 14 million new cases and 8.2 million cancer related deaths in 2012 (1).
The number of new cases is expected to rise by about 70% over the next 2 decades.
Among men, the 5 most common sites of cancer diagnosed in 2012 were lung, prostate, colorectum, stomach, and liver cancer.
Among women the 5 most common sites diagnosed were breast, colorectum, lung, cervix, and stomach cancer.
Around one third of cancer deaths are due to the 5 leading behavioural and dietary risks: high body mass index, low fruit and vegetable intake, lack of physical activity, tobacco use, alcohol use.
Tobacco use is the most important risk factor for cancer causing around 20% of global cancer deaths and around 70% of global lung cancer deaths.
Cancer causing viral infections such as HBV/HCV and HPV are responsible for up to 20% of cancer deaths in low- and middle-income countries (2).
More than 60% of world’s total new annual cases occur in Africa, Asia and Central and South America. These regions account for 70% of the world’s cancer deaths (1).
It is expected that annual cancer cases will rise from 14 million in 2012 to 22 within the next 2 decades (1).
Cancer is a generic term for a large group of diseases that can affect any part of the body. Other terms used are malignant tumours and neoplasms. One defining feature of cancer is the rapid creation of abnormal cells that grow beyond their usual boundaries, and which can then invade adjoining parts of the body and spread to other organs, the latter process is referred to as metastasizing. Metastases are the major cause of death from cancer.
The problem
Cancer is a leading cause of death worldwide, accounting for 8.2 million deaths in 2012 (1). The most common causes of cancer death are cancers of:
lung (1.59 million deaths)
liver (745 000 deaths)
stomach (723 000 deaths)
colorectal (694 000 deaths)
breast (521 000 deaths)
oesophageal cancer (400 000 deaths) (1).
What causes cancer?
Cancer arises from one single cell. The transformation from a normal cell into a tumour cell is a multistage process, typically a progression from a pre-cancerous lesion to malignant tumours. These changes are the result of the interaction between a person's genetic factors and 3 categories of external agents, including:
—> physical carcinogens, such as ultraviolet and ionizing radiation;
—>chemical carcinogens, such as asbestos, components of tobacco smoke, aflatoxin (a food contaminant) and arsenic (a drinking water contaminant); and
—>biological carcinogens, such as infections from certain viruses, bacteria or parasites.
WHO, through its cancer research agency, International Agency for Research on Cancer (IARC), maintains a classification of cancer causing agents.
Ageing is another fundamental factor for the development of cancer. The incidence of cancer rises dramatically with age, most likely due to a build up of risks for specific cancers that increase with age. The overall risk accumulation is combined with the tendency for cellular repair mechanisms to be less effective as a person grows older.

What is the second biggest cause of lung cancer in the world?