A number of benign and malignant tumours occur in the lungs but the primary lung cancer, commonly termed bronchogenic carcinoma, is the most common. The lung is also the commonest site for metastasis from carcinomas and sarcomas. A histologic classification of various benign and malignant tumours of lungs as recommended by the World Health Organisation

It is the most common primary malignant tumour in men inindustrialised nations and accounts for nearly one-third of all cancer deaths in both sexes. Currently, the incidence in females in the United States has already exceeded breast cancer as a cause of death in women. Cancer of the lung is a disease of middle and late life with peak incidence in 5th to 7th decades, after which there is gradual fall in its incidence.

ETIOPATHOGENESIS

1. Smoking :

2. Atmospheric pollution

3. Occupational causes

4. Dietary factors

5. Genetic factors

6. Chronic Scarring

TUBERCULOSIS

Tuberculosis (commonly shortened to TB) is an infection caused by the bacterium Mycobacterium tuberculosis. TB most commonly affects the lungs (pulmonary TB) but can also affect the central nervous system (CNS)(meningitis), lymphatic system, circulatory system (Miliary tuberculosis), genitourinary system, bones and joints.

Tuberculosis is one of the most deadly and common major infectious diseases today, infecting more than two billion people, or approximately one-third of the world's population. Nine million new cases of disease, resulting in two million deaths, occur annually, mostly in developing countries. However, developed countries are not spared the burden of tuberculosis.

Tissue response in tuberculosis represents classical example of chronic granulomatous inflammation in humans.the causative agent is tubercle bacillus or Koch bacillus called Mycobacterium tuberculousis causes tuberculosis in the lung and other tissues of the human body. The organism is a strict aerobe and thrives best in tissues with oxygen tension like in the apex of the lung.

Mode Of Transmission

1. Inhalation of organisms present in fresh cough droplets or in dried sputum form an open case of pulmonary tuberculosis.

2. Ingestion of the organisms leads to development of tonsillar or intestinal tuberculosis. This mode of infection of human tubercle bacilli is from self-swallowing of infected sputum of an open case of pulmonary tuberculosis, or ingestion of bovine tubercle bacilli from milk of diseased cows.

3. Inoculation of the organisms into the skin may rarely occur from infected postmorten tissue.

TB is spread by aerosol droplets expelled by people with active TB disease of the lungs when they cough, sneeze, speak, or spit. Each droplet is 5 ?m in diameter and contains 1 to 3 bacilli. Close contacts (people with prolonged, frequent, or intense contact) are at highest risk of becoming infected (typically a 22% infection rate). A person with untreated, active tuberculosis can infect an estimated 20 other people per year.